Skip Maine state header navigation
Mosquito-borne
Disease FAQ
Maine Center for Disease Control
Maine Board of Pesticides Control
Maine Department of Environmental Protection
University of Maine Cooperative Extension
Due to last year’s West Nile
virus and Eastern Equine Encephalitis activity, there has been increased
concern about mosquito-borne diseases in Maine. The Maine Centers for Disease
Control, the Maine Board of Pesticides Control, the Maine Department of
Environmental Protection, and the University of Maine Cooperative Extension have
collaborated to compile a selection of frequently asked questions, along with
their answers, about West Nile and Eastern Equine Encephalitis virus, arboviral
disease prevention, and mosquito control.
This information is arranged by topic, and will be updated regularly.
This document, as well as further information on arboviruses, their prevention, and Maine’s arboviral surveillance data can be found at http://www.maine.gov/dhhs/boh/ddc/west_nile_virus.htm.
Q. What is an arbovirus?
A. Arboviruses
(Arthropod-borne viruses) cause diseases such as West Nile
virus infection, eastern equine encephalitis, St. Louis encephalitis, Powassan
encephalitis, etc. They are viruses
that are transmitted by blood feeding arthropods like mosquitoes and ticks.
Arboviruses are maintained in nature in a cycle of transmission between an
animal host (the reservoir) and the mosquito or tick.
Q. How do
people get infected with West Nile (WNV) or eastern equine encephalitis (EEE)
virus?
A.
The main route of human infection with West Nile and EEE virus is through the
bite of an infected mosquito. Neither virus can be passed between
people by coughing, sneezing, shaking hands, sharing food, etc
Additional routes of human infection were
identified for WNV during the 2002 West Nile epidemic. It is important to note
that these other methods of transmission represent a very small proportion of
cases. Investigations have identified WNV transmission through transplanted
organs and through blood transfusions. There is one reported case of
transplacental (mother-to-child) WNV transmission, and one reported case of
transmission of WNV through breast-milk. Transmission in the laboratory has
also been reported.
Q. How are arboviruses
spread to humans or horses by mosquitoes?
A. Getting infected with an
arbovirus is a bit like winning the lottery. The chances of it happening are
very slim, but the consequences can be life-changing. The process of infection
works like this:
1)
A
female mosquito (of a species that bites both birds and mammals) first
must bite a bird infected with an arbovirus (male mosquitoes don’t bite).
2)
The
blood of the infected bird contains arbovirus particles, so the mosquito biting
the bird draws in the disease-causing virus with her blood meal.
3)
The
mosquito digests her meal for several days, and then lays her eggs. While her
meal is being digested and she is laying eggs, the virus particles move from
the insect’s gut to her salivary glands.
4)
After
the mosquito lays her eggs (if she is lucky enough to live that long), she
seeks another blood meal. This time she bites a horse or a human.
5)
She
lands, inserts her mouthparts, and injects saliva. Along with her saliva, she
injects some of the virus particles. If enough virus particles are in the
saliva, the person or horse will be infected. This is the same process by other
animals are infected also.
Please note: Humans and equines are “dead-end” hosts for WNV and EEE. Mosquitoes that bite humans or equines infected with WNV or EEE don’t pick up enough virus particles to pass the disease along to the next human (or animal) they bite.
Q. Do all mosquitoes spread WNV and EEE?
A. No.
There are approximately 42 different species of mosquitoes in
Maine. Some of them have habitats that
overlap, and others have separate habitats based on their specific breeding
requirements. Some mosquitoes feed on
birds, some on mammals, and a few on both birds and mammals.
The mosquitoes of most
concern are those that feed on both birds and mammals; these are called
“bridge” vectors. This type of mosquito
may become infected with an arbovirus by feeding on an infected bird, and then
later feed on a human, thus providing the “bridge” that allows arboviruses to
spread to humans.
Q. If I live in an area where birds or
mosquitoes with WNV or EEE have been reported and a mosquito bites me, am I
likely to get sick?
A. No.
Even in areas where these viruses are circulating, very few mosquitoes are
infected. Even if the mosquito is infected, less than 1% of people who get
bitten and become infected will get severely ill. The chances you will become
severely ill from any one mosquito bite are extremely small.
Q. Can you get WNV or EEE directly from other
insects or ticks?
A. Infected
mosquitoes are the primary source for WNV and EEE. Although ticks infected with
West Nile virus have been found in Asia and Africa, their role in the
transmission and maintenance of the virus is uncertain. However, there is no
information to suggest that ticks played any role in cases of either disease
identified in the United States.
Q. Can you get WNV or EEE from another person?
A. No.
WNV and EEE are NOT transmitted from person-to-person. For example, you
cannot get either virus from touching or kissing a person who has WNV or EEE,
or from a health care worker who has treated someone with either disease.
Q. Are all wetlands breeding grounds for arboviruses?
A. No. The few potential WNV vector species primarily
breed in two types of areas: stagnant water and high elevation salt marsh
pools. The stagnant water areas can be
found in artificial containers such as bird baths, tires, buckets, kiddy pools,
stormwater and catch basins, drainage ditches, etc. where water may not be
regularly exchanged and becomes stagnant.
Many of these structures can be emptied regularly to eliminate mosquito
breeding conditions. High elevation salt
marsh pools are located above the normal high tide line in marine areas. These areas are typically only flooded
during significant storms or other extremely high tide events, often only once
per month. Some of them contain fish
that will act as natural predators, keeping the mosquitoes from surviving and
breeding. However, the pools without
fish provide good mosquito breeding habitat.
The mosquito primarily
responsible for maintaining EEE in nature rarely feeds on humans, but is
important because it infects birds, which can then infect mosquitoes that feed
on birds AND mammals, like humans and horses. This mosquito, called a
maintenance vector, primarily breeds in acidic freshwater wetlands like red
maple and cedar swamps or bogs, which represent only a few of the many types of
freshwater wetland habitats found in Maine.
All wetlands need to be
respected and preserved, as they:
Q. I think I have symptoms of WNV or EEE. What
should I do?
A.
Contact your health care provider if you have concerns about your health. If
you or your family members develop symptoms such as high fever, confusion,
muscle weakness, and severe headaches, you should see your doctor immediately.
Q. How do health care providers test for WNV,
EEE, or other arboviruses?
A.
Arboviral infection can be suspected in a person based on clinical symptoms and
patient history. Laboratory testing of blood or cerebrospinal fluid (CSF)
samples is required for a confirmed diagnosis. These tests may not be positive
when symptoms first occur, but will usually be positive in infected people
within 8 days of the beginning of symptoms.
Persons that test positive for an arboviral
infection by these tests will have a second confirmation test completed at the
national Centers for Disease Control.
Q. How is WNV or EEE treated?
A.
There is no specific treatment for WNV or EEE. In more severe cases, intensive
supportive therapy is indicated, often involving hospitalization, intravenous
fluids, airway management, respiratory support (ventilator), prevention of
secondary infections (pneumonia, urinary tract, etc.), and good nursing care.
Q. If an arbovirus test is a “false positive”
what does that mean?
A. A
“false positive” occurs when an initial tests indicates that a person does have
WNV or EEE, but a later, more specific tests indicates that the person does not
actually have the infection. While it is important for the Maine CDC to get an
accurate picture of where people are being infected in order to focus
prevention and control efforts, the result does not have a great impact on the
individual person. There is no specific treatment that the person would receive
due to WNV or EEE. The person may want to work with their physician to see if
another cause of the illness needs to be identified.
General
Q. How many types of animals have been
found to be infected with West Nile or EEE virus?
A. The
vast majority of WNV and EEE infections have been identified in birds. WNV has
been shown to infect horses, llamas, alpacas, bats, chipmunks, skunks,
squirrels, and domestic rabbits. A
relatively small number of WNV infected dogs (<40) and only 1 WNV infected
cat have been reported nationally during 2003. Experimentally infected dogs
showed no symptoms after infection with WNV. Some infected cats exhibited mild,
nonspecific symptoms during the first week after infection--for the most part
only showing a slight fever and slight lethargy. It is unlikely that most pet owners would notice any unusual
symptoms or behavior in cats or dogs that become infected with WNV.
EEE can also infect horses,
llamas, and alpacas, and although cloven-hoofed livestock may be susceptible,
their level of risk is unknown. Some states have discovered whitetail deer
infected with EEE, but no one has studied just how serious those infections
are. Emus and Ring-necked pheasants are very susceptible to EEE infection, and
infected pheasants can serve as a source of virus for mosquitoes to spread the
disease further.
Q. Can I use insect repellent on my pets and
livestock?
A.
DEET-based repellents, which are recommended for humans, are not
approved for veterinary use (largely because animals tend to ingest them by
licking.) Talk with your veterinarian for advice about the appropriate product
for use on your pets or livestock.
Q. What are the signs of WNV or EEE in horses?
A. Clinical signs of WNV in horses include
stumbling, depression, incoordination, and weakness of limbs (partial paralysis
or inability to stand), and muscle twitching.
However, some infected horses may not show any signs. Although about two-thirds of infected horses
that become ill will survive and have a full recovery, West Nile virus can and
has caused deaths in horses.
Clinical signs of EEE in
horses are similar to those of WNV, but EEE is serious in equines (horses and their relatives) and usually fatal.
Q. How do the horses become infected with WNV or
EEE?
A. The
same way humans become infected—by the bite of infectious mosquitoes. The virus
is located in the mosquito's salivary glands. When mosquitoes bite or
"feed" on the horse, the virus is injected into its blood system. The
virus then multiplies and may cause illness. The mosquitoes become infected
when they feed on infected birds or other animals.
Q. Can I get infected with WNV or EEE by caring
for an infected horse?
A.
These diseases are transmitted by infectious mosquitoes. There is no documented
evidence of person-to-person or animal-to-person transmission of WNV or EEE.
Normal veterinary infection control precautions should be followed when caring
for a horse suspected to have these or any viral infection.
Q. Can a horse infected with WNV or EEE infect
horses in neighboring stalls?
A. No. There is no documented evidence that WNV
or EEE is transmitted between horses.
Q. Can I vaccinate my horse against WNV and EEE?
A.
There are WNV and EEE vaccines available for equines. Please note that the vaccines offer NO cross-protection; i.e.,
the WNV vaccine does not protect against EEE, and vice versa.
To be protected, horses must be fully vaccinated
or boostered at least two weeks before exposed to mosquitoes. Please consult
your veterinarian for more information.
Q. What is the treatment for a horse that has
WNV or EEE? Should it be destroyed?
A.
There is no reason to destroy a horse just because it has WNV or EEE. Treatment
would be supportive and consistent with standard veterinary practices for
animals infected with a viral agent.
Q. Is there a risk of getting infected with WNV
or EEE if I eat turkey or another animal that has been infected with the virus?
A. There
is no evidence that people can become infected with WNV or EEE from eating
infected meat. The small, theoretical risk of infection can be eliminated by
proper handling and thorough cooking of meat before it is consumed.
Several well-known and potentially serious food-borne illnesses can occur when
turkey and other meats are improperly handled or undercooked. For more
information on food safety, please see: http://www.cdc.gov/foodsafety/.
A small number of squirrels have tested positive
for the West Nile virus. There is no evidence that people could become infected
with the West Nile virus by being near an infected squirrel or in the yard with
a dead one. However, the presence of an infected squirrel does mean that there
could be infected mosquitoes nearby, and people should use protective clothing
and repellent, and avoid maintaining mosquito-breeding sites on their property.
Q. What is known about the risk of WNV or EEE
from dried, uncooked meat (jerky)?
A. There are no published studies that directly address this question.
Most studies indicate that while mammals can become infected with West Nile or
EEE virus, they do not develop high concentrations of virus in their blood or
tissues. Although it is unlikely that dried meat from mammals would have much
virus present, and probable that gastrointestinal digestion would further limit
the possibility of infectiousness, there is insufficient evidence to determine
whether dried meat presents a risk of WNV or EEE to humans or other animals.
Q. Are duck and other wild game hunters at risk for WNV or EEE infection?
A. Because of their outdoor exposure, game hunters may be at risk if they
are bitten by mosquitoes in areas with arboviral activity. The extent to which
WNV or EEE may be present in wild game is unknown.
Q. What should wild game hunters do to protect
themselves against WNV and EEE?
A.
Hunters should follow the usual precautions when handling wild animals. If they
anticipate being exposed to mosquitoes, they should apply insect repellent to
clothing and skin, according to label instructions, to prevent mosquito bites.
Hunters should wear gloves when handling and cleaning animals to prevent blood
exposure to bare hands and meat should be cooked thoroughly.
Q. What is
Maine doing about WNV and EEE?
A. The Maine Center for Disease Control has developed an Arboviral
Surveillance system to track the occurrence of WNV and EEE in Maine, generally
beginning in mid-June and lasting through to mid-October. Surveillance efforts
include adult mosquito trapping and testing, collecting dead bird data, testing
dead birds, llamas, alpacas, and horses, and testing people who are ill with
symptoms similar to those of an arbovirus infection.
By doing this, prevention and
education efforts can be focused on higher risk areas, including showing the
public how to protect themselves and their families from diseases. In addition,
other state agencies, health professionals and non-governmental groups have
worked together since 2000 to increase awareness and promote preventive
measures. Further information on arboviruses, their prevention, and Maine’s
arboviral surveillance data can be found at http://www.maine.gov/dhhs/boh/ddc/west_nile_virus.htm.
Q. What should I do if I
find a dead bird?
A.
The usual bird surveillance season in Maine is from June through
October. If you find a dead bird in
these months, call the Maine CDC Dead Bird Reporting Line at 1-888-697-5846,
and you
will be provided with further instruction. Testing of dead birds in 2006 will limited to corvids
(ravens, crows, and blue jays), unless there are unusual circumstances. Captive
pheasants and emus are notable exceptions, and owners of these species or veterinarians
providing care for these species are also encouraged to call the Bird Reporting
Hotline if they detect severe illness or death in their birds. Even though not all dead birds will be collected or tested,
all reports will be recorded; this information can be very useful in detecting
clusters of dead birds that occur over time, and can indicate if and when the
testing protocol should be modified.
Q. Should I report any
other ill or dead animals?
A.
Equines, llamas, and alpacas make
up an important component of the Maine CDC Arboviral Surveillance program. Owners and veterinarians are urged to report
cases of illness in these species so that the Maine CDC can determine if
arboviral testing is appropriate. Any
equine, llama, or alpaca that dies with neurological abnormalities, or is
euthanized due to illness with neurological abnormalities, should be reported
to either the Maine CDC Disease Reporting Hotline at 1-800-821-5821
or the Bird Reporting Hotline at 1-888-697-5846.
Only
dead animals of these species can be tested for arboviral infection, as they
must first be tested for rabies. If a veterinarian, while treating an animal of
these species, obtains serology results positive for an arbovirus, the Maine
CDC urges them to report those results to the phone number stated above, even
if the animal survives. It is also
important that a WNV/EEE vaccination history be submitted with any specimens
and included in any reports. Reports of
potential arboviral cases in these species can be made year-round.
Q: What is West Nile virus?
A.
West Nile virus (WNV) is commonly found in Africa, West Asia, and the Middle
East. It is closely related to St. Louis encephalitis virus, another arbovirus
found in the United States. WNV can infect humans, birds, mosquitoes, horses
and some other mammals.
Q. How long has West Nile virus been in the
U.S.?
A. It
is not known exactly how long it has been in the U.S., but it was first
detected in North America during the summer of 1999, when infection with the
virus caused an outbreak of illnesses in New York City. Within the next four years, the virus spread
to almost all areas of North America. The continued expansion of West Nile
virus in the United States indicates that it is permanently established.
Q. Is the disease seasonal in its occurrence?
A. In
temperate zones, West Nile encephalitis cases occur primarily in the late
summer or early fall. In the southern climates where temperatures are milder,
West Nile virus can be transmitted year round.
Q. What parts of Maine are affected by West Nile Virus? Is it spreading further?
A. WNV was first identified
in Maine in 2001. During 2003, West
Nile Virus was documented (through testing of dead birds and mosquitoes) in
twelve of Maine’s 16 counties. In 2005,
22 birds tested positive for WNV in Maine, one in Cumberland County, and the
rest in York County.
Experts believe that WNV is well established in the ecologic systems of
most areas in the United States and that it continues to spread and that it will
remain with us for many years to come. The Maine Center for Disease Control
recommends that citizens and municipalities assume that the risk of acquiring
WNV infection exists in all Maine
communities.
Q. How many cases of West Nile disease in humans
have occurred in the U.S., and in Maine specifically?
A. The
national Centers for Disease Control and Prevention (CDC) maintains West Nile
virus infection data for the United States at http://www.cdc.gov/ncidod/dvbid/westnile/surv&control.htm. In 2005, there were 12,819 human WNV cases
in the United States. Maine, New Hampshire and Vermont were among the eight
states that had no human cases. Massachusetts had six cases and New York had
14. The really high numbers of human cases (more than 100) occurred in central
and western states.
To date, there have been NO human cases
of West Nile virus infection ever identified in Maine.
Q. What proportion of people with severe illness
due to West Nile virus die?
A.
Among those with severe illness due to West Nile virus, case-fatality rates
range from 3% to 15% and are highest among the elderly, who appear to be more
likely to get severe illness from infection with West Nile virus than do
younger individuals. Less than 1% of people who become infected with West Nile
virus will develop severe illness -- most people who get infected do not
develop any disease at all.
Q. Who is at risk for getting West Nile
encephalitis?
A.
Anyone who is exposed to mosquitoes is potentially at risk of mosquito-borne
disease. All residents of areas where
virus activity has been identified are at risk of getting West Nile
encephalitis; persons over 50 years of age have the highest risk of severe
disease. It is unknown if immunocompromised persons are at increased risk for
WNV disease.
Q. Is a woman's pregnancy at risk if she gets
infected with West Nile virus?
A. There
is one documented case of transplacental (mother-to-child) transmission of WNV
in a human. Although the newborn in this case was infected with WNV at birth
and had severe medical problems, it is unknown whether the WNV infection itself
caused these problems or whether they were coincidental. More research will be
needed to improve our understanding of the relationship - if any - between WNV
infection and adverse birth outcomes.
Nevertheless, pregnant women should take
precautions to reduce their risk for WNV and other arboviral infections by
avoiding mosquitoes, using protective clothing, and using repellents containing
DEET (See the Personal
Measures to Prevent WNV and EEE Infection section). When WNV transmission
is occurring in an area, pregnant women who become ill should see their health
care provider, and those whose illness is consistent with acute WNV infection,
should undergo appropriate diagnostic testing.
Q. Are infants at higher risk than other groups
for illness with West Nile virus?
A. No. West Nile virus illnesses in children younger than 1 year old are
infrequent. During 1999-2001, no cases in children younger than one year of age
were reported in the United States. In 2002, 2,500 total West Nile Virus
disease cases were reported in the United States, and only six occurred in
children less than one year of age.
Q. What are the symptoms of West Nile virus
(WNV) infection?
A. Infection
with WNV can be asymptomatic (no symptoms), or can lead to West Nile
fever or severe West Nile disease. It is estimated that about 20% of people who become
infected with WNV will develop West Nile fever. Symptoms
include fever, headache, tiredness, and body aches, occasionally with a skin
rash (on the trunk of the body) and swollen lymph glands. While the illness can
be as short as a few days, even healthy people have reported being sick for
several weeks.
The symptoms of severe disease
(also called neuroinvasive disease, such as West Nile
encephalitis or meningitis or West Nile
poliomyelitis) include headache, high fever, neck stiffness, stupor,
disorientation, coma, tremors, convulsions, muscle weakness, and paralysis. It
is estimated that approximately 1 in 150 persons infected with the West Nile
virus will develop a more severe form of disease. Serious illness can occur in
people of any age; however people over age 50 and some immunocompromised
persons (for example, transplant patients) are at the highest risk for getting
severely ill when infected with WNV.
Most people (about 4 out of 5) who are
infected with West Nile virus will not develop any type of illness (an
asymptomatic infection); however you cannot know ahead of time if you'll get
sick or not when infected.
Q. What is the incubation period in humans
(i.e., time from infection to onset of disease symptoms) for West Nile disease,
and how long do symptoms last?
A.
The incubation period of West Nile disease is usually 2 to 15 days. Symptoms of
West Nile fever will generally last a few days, although even some healthy
people report having the illness last for several weeks. The symptoms of severe
disease (encephalitis or meningitis) may last several weeks, although
neurological effects may be permanent.
Q. What is meant by West Nile encephalitis,
West Nile meningitis, West Nile poliomyelitis, “neuroinvasive disease” and West
Nile fever?
A. The
most severe type of disease due to a person being infected with West Nile virus
is sometimes called “neuroinvasive disease,” because it affects a person's
nervous system. Specific types of neuroinvasive disease include: West Nile
encephalitis, West Nile meningitis, West Nile meningoencephalitis and West Nile
poliomyelitis. Encephalitis refers to an inflammation of the brain, meningitis
is an inflammation of the membrane around the brain and the spinal cord,
meningoencephalitis refers to inflammation of the brain and the membrane
surrounding it, and poliomyelitis refers to an inflammation of the spinal cord.
West Nile Fever is another type of illness that
can occur in people who become infected with the virus. It is characterized by
fever, headache, tiredness, aches and sometimes rash. Although the illness can
be as short as a few days, even healthy people have been sick for several
weeks.
Q. If I have West Nile Fever, can it turn
into West Nile encephalitis?
A. When someone is infected with West Nile virus (WNV)
they will typically have one of three outcomes: No symptoms (most likely), West
Nile fever (WNF in about 20% of people) or severe West Nile disease, such as
meningitis or encephalitis (less than 1% of those who get infected). If you
develop a high fever with severe headache, consult your health care provider.
West Nile fever is characterized by symptoms
such as fever, body aches, headache and sometimes swollen lymph glands and
rash. West Nile fever generally lasts only a few days, though in some cases
symptoms have been reported to last longer, even up to several weeks. West Nile
fever does not appear to cause any permanent health effects. There is no
specific treatment for WNV infection. People with West Nile fever recover on
their own, though symptoms can be relieved through various treatments (such as
medication for headache and body aches, etc.).
Some people may develop a brief, WNF-like illness
(early symptoms) before they develop more severe disease, though the percentage
of patients in whom this occurs is not known.
Occasionally, an infected person may develop
more severe disease such as “West Nile encephalitis,” “West Nile meningitis” or
“West Nile meningoencephalitis.” Encephalitis refers to an inflammation of the
brain, meningitis is an inflammation of the membrane around the brain and the
spinal cord, and meningoencephalitis refers to inflammation of the brain and
the membrane surrounding it. Although there is no treatment for WNV infection
itself, the person with severe disease often needs to be hospitalized. Care may
involve nursing, IV fluids, respiratory support, and prevention of secondary
infections.
Q. What
is eastern equine encephalitis?
A. Eastern equine
encephalitis (EEE) is a member of the family Togaviridae, genus Alphavirus,
and is closely related to western and Venezuelan equine encephalitis
viruses. It occurs primarily in the eastern half of
the US. Because of the high case fatality rate, EEE is regarded as one of the
more serious mosquito-borne diseases in the United States.
The primary EEE
transmission cycle is between birds and mosquitoes. Several species of
mosquitoes can become infected with EEE virus. The most important mosquito in
maintaining the enzootic (animal-based, in this case bird-mosquito-bird)
transmission cycle is Culiseta melanura.
Q. What
are the symptoms of EEE, and how serious is it?
A. Symptoms range from mild flu-like illness to encephalitis (inflammation of the brain), coma and death.
The EEE case fatality rate
(the % of persons who develop the disease who will die) is 35%, making it one
of the most serious mosquito-borne diseases in the US. It is estimated that 35% of people who
survive EEE will have mild to severe nervous system effects.
Q. What
parts of Maine are affected by eastern equine encephalitis?
A. EEE
was first identified in Maine in 2005.
During 2005, twelve birds tested positive for EEE, two from Cumberland
County, and ten from York County. Also from York County, two horses and one
mosquito pool (the bird-feeding Culiseta
melanura) tested positive for EEE.
Due to our 2005 surveillance data, and the EEE activity in the parts of
New Hampshire that border Maine, southwestern Maine appears to be at the
greatest risk of EEE activity. However, the Maine Center for Disease Control
recommends that citizens and municipalities assume that the risk of EEE exists
in all Maine communities, and to
practice the prevention methods described in the Personal Measures to Prevent WNV
and EEE Infection section.
Q. How
many and where have human disease cases occurred?
A. From 1964 to
2004, there have been 220 confirmed cases of human EEE in the United States,
averaging 5 cases per year (with a range from 0-15 cases). The states with the traditionally largest
number of cases are Florida, Georgia, Massachusetts, and New Jersey.
In
2005, there were 20 human cases of EEE in the United States. New Hampshire had
the most with seven cases (six more than the previous year), two of which died.
Florida had five, Massachusetts four, Alabama two, and South Carolina and
Georgia one each.
There have been NO
human EEE cases identified in Maine to date.
The EEE transmission cycle between birds and bird-feeding mosquitoes is most common in coastal areas and freshwater swamps. Human cases occur relatively infrequently, largely because the primary transmission cycle takes place in swampy areas where human populations tend to be limited.
Q. Who is at risk for developing EEE?
A. Residents of and
visitors to areas with an established presence of the virus, people who engage
in outdoor work and recreational activities, and persons over age 50 and
younger than age 15 seem to be at greatest risk for developing severe disease.
Q. What can I do to reduce my risk of becoming
infected with West Nile and EEE virus?
A. Here are preventive measures that you and your family
can take:
Protect yourself from
mosquito bites:
·
Apply insect repellent
to exposed skin. Generally, the more active ingredient a repellent contains the
longer it can protect you from mosquito bites. A higher percentage of active
ingredient in a repellent does not mean that your protection is better—just
that it will last longer. Choose a repellent that provides protection for the
amount of time that you will be outdoors.
o
Repellents may irritate
the eyes and mouth, so avoid applying repellent to the hands of children.
o
Whenever you use an
insecticide or insect repellent, be sure to read and follow the manufacturer's
DIRECTIONS FOR USE, as printed on the product.
·
Spray clothing with repellents
containing permethrin or another EPA-registered repellent since mosquitoes may
bite through thin clothing. Do not apply repellents containing permethrin
directly to exposed skin. Do not apply repellent to skin under your clothing.
·
When weather permits,
wear long-sleeved shirts and long pants whenever you are outdoors.
·
Place mosquito netting
over infant carriers when you are outdoors with infants.
·
Consider staying indoors
at dawn, dusk, and in the early evening, which are peak mosquito biting times.
·
Install or repair window
and door screens so that mosquitoes cannot get indoors.
Water gardens, poorly adjusted gutters,
discarded tires, pool covers, and rain barrels are examples of sites that can
support high numbers of mosquito larvae. Help reduce the number of mosquitoes
in areas outdoors where you work or play, by draining sources of standing
water. In this way, you reduce the number of places mosquitoes can lay their
eggs and breed, and ultimately can reduce the number of adult mosquitoes.
Q. What Are Mosquito
Traps, “Bug Zappers”, and Ultrasonic Devices?
Are They Effective?
A.
Until recently, traps worked to collect some specimens and determine
which species were present, but didn’t control mosquitoes. Now some
traps touted as potential mosquito control devices. Some of the mosquito traps
now available use carbon dioxide as their principal attractant, and others add
octenol or other attractants. Some of these newer traps capture many times the
number of mosquitoes as their predecessors, and may help reduce mosquito annoyance.
Results, however, can vary, and no reports have appeared in the scientific
literature that measure mosquito numbers or bite counts to compare traps with
other control measures. So it is really not known how effective they are at
reducing the risk of getting bitten, especially by the critical species that
spread arboviruses. Mosquito traps on the market can be very expensive. You can
buy many years’ worth of repellent for the cost of one trap.
Electric bug “zappers” are
commonly sold, and some promotional literature claims they kill mosquitoes.
While these devices may “zap” the occasional mosquito, they don’t reduce
mosquito problems. However, the zappers do kill a large number of
harmless insects and many beneficial insects. The ultraviolet light attracts
beetles, flies, moths, caddisflies and many other insects, but few pests. These products are ineffective mosquito
control devices.
Ultrasonic mosquito
repellents also have NO effect in
reducing mosquito problems, and their claims of effectiveness are misleading or
false.
Q. What can be done to prevent outbreaks of West
Nile and EEE infections?
A. Prevention and control of these and other
arboviral diseases is most effectively accomplished through integrated vector
management programs. These programs should include surveillance for West Nile
and EEE virus activity in mosquito vectors, birds, horses, other animals, and
humans, and implementation of appropriate mosquito control measures to reduce
mosquito populations when necessary. Additionally, when virus activity is
detected in an area, residents should be alerted and advised to increase
measures to reduce contact with mosquitoes.
Q. Are there human
vaccines against West Nile or Eastern Equine encephalitis?
A.
There are currently NO human vaccines available for either West Nile or
EEE virus.
Q. Are there
equine vaccines against West Nile or Eastern Equine encephalitis?
A. There are
vaccines available to protect horses from both WNV and EEE. Consult your
veterinarian for more information.
Q. Should people take the West Nile and EEE virus
vaccines that are licensed for use in horses?
A.
No. These vaccines have not been studied in humans and could be harmful. Veterinary vaccines and other veterinary
drugs should never be used in humans.
Q. Why should I use insect repellent?
A. Insect repellents can help reduce exposure to mosquito
bites that may carry viruses such as West Nile or EEE virus that can cause
serious illness and even death. Using insect repellent allows you to continue
to play and work outdoors with a reduced risk of mosquito bites.
Q. When should I use mosquito repellent?
A. Apply repellent when you are going to be outdoors. Even if
you don’t notice mosquitoes there is a good chance that they are around. Many
of the mosquitoes that carry West Nile and EEE virus bite between dusk and
dawn. If you are outdoors around these times of the day, it is especially
important to apply repellent.
Q. How often should repellent be
reapplied?
A. In general, you should re-apply repellent if you are being
bitten by mosquitoes. Always follow the directions on the product you are
using. Sweating, perspiration or getting wet may mean that you need to re-apply
repellent more frequently.
Q. How does mosquito repellent work?
A.
Female mosquitoes bite people and animals because they need the protein found
in blood to help develop their eggs. Mosquitoes are attracted to people by skin
odors and carbon dioxide from breath. The active ingredients in repellents make
the person unattractive for feeding. Repellents do not kill mosquitoes.
Repellents are effective only at short distances from the treated surface, so
you may still see mosquitoes flying nearby.
Q. Which mosquito repellents work best?
A.
The Maine CDC recommends using products that have been shown to work in
scientific trials, and that contain active ingredients which have been
registered with the EPA (http://www.epa.gov/pesticides/health/mosquitoes/insectrp.htm#choosing)
for use as insect repellents on skin or clothing. When EPA registers a
repellent, they evaluate the product for efficacy and potential effects on
human beings and the environment. EPA registration means that EPA does not
expect a product, when used according to the instructions on the label, to
cause unreasonable adverse effects to human health or the environment.
Of the active ingredients registered with the EPA, two have demonstrated a
higher degree of efficacy in the peer-reviewed, scientific literature (For more
detailed information, see http://www.cdc.gov/ncidod/dvbid/westnile/publications.htm).
Products containing these active ingredients typically provide longer-lasting
protection than others:
• DEET (N,N-diethyl-m-toluamide)
• Picaridin (KBR 3023)
Oil of lemon eucalyptus [active ingredient:
p-menthane 3,8-diol (PMD)], a plant- based repellent, is also registered with
EPA. In two recent scientific publications, when oil of lemon eucalyptus was
tested against mosquitoes found in the US it provided protection similar to
repellents with low concentrations of DEET.
Q. How does the percentage of active
ingredient in a product relate to the amount of protection it gives?
A. Typically,
the more active ingredient a product contains the longer it provides protection
from mosquito bites. The concentration of different active ingredients cannot
be directly compared (that is, 10% concentration of one product doesn’t mean it
works exactly the same as 10% concentration of another product.)
DEET is an effective active ingredient found in
many repellent products and in a variety of formulations. Based on a 2002 study
(Fradin and Day, 2002; See http://www.cdc.gov/ncidod/dvbid/westnile/publications.htm):
• A product containing 23.8% DEET provided an
average of 5 hours of protection from mosquito bites.
• A product containing 20% DEET provided almost 4 hours of protection
• A product with 6.65% DEET provided almost 2 hours of protection
• Products with 4.75% DEET were both able to provide roughly 1 and a half hour
of protection.
These examples represent results from only one
study and are only included to provide a general idea of how such products may
work. Actual protection will vary widely based on conditions such as
temperature, perspiration, and water exposure.
Choose a repellent that provides protection for the amount of time that
you will be outdoors. A product with a higher percentage of active ingredient
is a good choice if you will be outdoors for several hours while a product with
a lower concentration can be used if time outdoors will be limited. If you are
outdoors for a longer time than expected and start to be bitten by mosquitoes,
simply re-apply repellent (following label instructions).
Q. Why does the Maine CDC
recommend certain types of insect repellent?
A. The
Maine CDC recommends products containing active ingredients which have been
registered with the EPA for use as insect repellents on skin or clothing.
All of the EPA-registered active ingredients have demonstrated repellency;
however, some provide longer lasting protection than others. Additional
research reviewed by the Maine CDC suggests that repellents containing DEET
(N,N-diethyl-m-toluamide) or picaridin (KBR 3023) typically provide
longer-lasting protection than the other products and oil of lemon eucalyptus
(p-menthane-3,8-diol) provides longer lasting protection than other plant-based
repellents. Permethrin is another long-lasting repellent that is intended for
application to clothing and gear, but not directly to skin. In general, the
more active ingredient (higher concentration) a repellent contains, the longer
time it protects against mosquito bites.
People who are concerned about using repellents
may wish to consult their health care provider for advice. The Maine Board of
Pesticides Control is a local source for insect repellent information, and can
be reached at 1-207-287-2731, or http://www.maine.gov/agriculture/pesticides/public/repellents.htm.
The National Pesticide Information Center (NPIC) can also provide information
through a toll-free number, 1-800-858-7378 or http://npic.orst.edu/.
Q. How can you know
which active ingredient a product contains?
A. Check the product
label if you have questions-–repellents must specify their active ingredients.
In some cases you will note the chemical name in addition to/instead of the
“common” name:
• DEET is N,N-diethyl-m-toluamide, Dimethyl-m-toluamide + related isomers, or
N,N-Dimethyl-m- toluamide m-meta
DEET + related isomers
• Picaridin (trade name KBR 3023), sometimes known as “Bayrepel,” is 2-(2-hydroxyethyl)-1-piperidinecarboxylic
acid 1-methylpropyl ester
• The active ingredient
in oil of lemon eucalyptus is p-menthane 3,8-diol (PMD)
Q. What is permethrin?
A. Certain products which contain permethrin are
recommended for use on clothing, shoes, bed nets, and camping gear, and are
registered with EPA for this use. Permethrin is highly effective as an
insecticide and as a repellent. Permethrin-treated clothing repels and kills
ticks, mosquitoes, and other arthropods and retains this effect after repeated
laundering. The permethrin insecticide should be reapplied following the label
instructions. Some commercial garments are available pretreated with
permethrin.
Q. Where can I find these repellents?
A.
Most of these repellents are sold at multiple retail, discount and drug stores.
A wider selection may be available at “outdoor” stores or in hunting and
camping sections.
Q. Where can I find more information
about picaridin?
A. A technical fact sheet covering picaridin is available from
the EPA at http://www.epa.gov/opprd001/factsheets/picaridin.pdf, or
contact the Maine Board of Pesticides Control at 1-207-287-2731.
Q. What are some general considerations
to remember when using insect repellents?
A.
Always follow the requirements appearing on the product label.
• Use enough repellent to cover exposed skin or clothing. Don't apply repellent
to skin that is under clothing. Heavy application is not necessary to achieve
protection.
• Do not apply repellent to cuts, wounds, or irritated skin.
• After returning indoors, wash treated skin with soap and water. (This may
vary depending on the product. Check the label.)
• Do not spray aerosol or pump products in enclosed areas.
• Do not spray aerosol or pump products directly to your face. Spray your hands
and then rub them carefully over the face, avoiding eyes and mouth.
Q. What are some reactions to be aware of
when using insect repellents?
A.
Use of repellents products may cause skin reactions in rare cases. Most product
labels also note that eye irritation can occur if product gets in the eye. If
you suspect a reaction to a product, discontinue use, wash the treated skin,
and call the poison center at 1-800-222-1222. If product gets in the eyes flush
with water and consult a health care provider or the poison center. If you go
to a doctor, take the product label with you.
Q. Can insect repellents be used on
children?
A.
Repellent products must state any age restriction. If there is none, EPA has
not required a restriction on the use of the product.
Since it is the most widely available repellent, many people ask about the use
of products containing DEET on children. No definitive studies exist in the
scientific literature about what concentration of DEET is safe for children. No
serious illness has been linked to the use of DEET in children when used
according to manufacturer’s recommendations.
The American Academy of Pediatrics (AAP) Committee on Environmental
Health has updated their recommendation for use of DEET products on children in
2003, available at http://www.aap.org/family/wnv-jun03.htm,
citing: "Insect repellents containing DEET (N,N-diethyl-m-toluamide, also
known as N,N-diethyl-3-methylbenzamide) with a concentration of 10% appear to
be as safe as products with a concentration of 30% when used according to the
directions on the product labels." AAP recommends that repellents with
DEET should not be used on infants less than 2 months old.
AAP has not yet issued specific recommendations
or opinions concerning the use of picaridin or oil of lemon eucalyptus for
children.
According to the label, oil of lemon
eucalyptus products should NOT be used on CHILDREN UNDER 3 YEARS of age.
Parents should choose the type and concentration
of repellent to be used by taking into account the amount of time that a child
will be outdoors, exposure to mosquitoes, and the risk of mosquito-transmitted
disease in the area.
If you are concerned about using repellent
products on children you may wish to consult a health care provider for advice,
the Maine Board of Pesticides Control at 1-207-287-2731, or contact the
National Pesticide Information Center (NPIC) through their toll-free number,
1-800-858-7378 or at http://npic.orst.edu/.
Q. What guidelines are available for
using a repellent on children?
A.
Always follow the recommendations appearing on the product label when using
repellent:
• When using repellent on a child, apply it to your own hands and then rub them
on your child. Avoid children's eyes and mouth and use it sparingly around
their ears.
• Do not apply repellent to children's hands. (Children may tend to put their
hands in their mouths.)
• Do not allow young children to apply insect repellent to themselves; have an
adult do it for them.