ASIAN TIGER MOSQUITO
©David B. Fankhauser, Ph.D.,
(Enlarge: Those are its eggs to
the L in the enlarged picture.
of West Nile Virus:
( Image from the
CDC site on WNV )
|WEST NILE VIRUS UPDATE:
The current epidemic in the United States of West Nile Virus (WNV) has
focused attention on mosquitoes as vectors of this disease. WNV
made its appearance in the U.S. in 1999, and during the Summer of 2000,
numerous cases arose in and around New York City. Deaths of
a number of patients in Greater New York raised concern about the
leading to wide-spread spraying of that area with insecticide.
has now (August 2002) been detected in mosquitoes and/or birds
all of the Eastern U.S., and has caused documented illness in
200 humans with the deaths of around 20. Members of the mosquito genus Culex
are most frequently associated with its transmission, but Asian Tiger
have also been found carrying the virus. Although Aedes albopictus
has not been demonstrated to transmit WNV to humans so far, we expect
it may be implicated with further study. The rapid spread
the Asian Tiger Mosquito and its proliferating numbers increase the
of it transmitting the disease.
West Nile Fever Transmission: Like other examples of arthropod borne viral (arboviral) encephalitis, West Nile Fever is caused by an enveloped "+" single stranded RNA virus, a member of the flavivirus group. The preferred host for this virus is birds, especially members of the family Corvidae (Crows, Bluejays, etc) which presumably constitute the reservoir for the virus. (Dead Crows are often the first sign of the virus' presense in a community.) The virus is transmitted by female mosquitoes when, after picking up the virus from an infected bird, they take another blood meal and transmit the virus to incidental species such as horses and less frequently, humans. Transmission of the virus from one human to another by a mosquito has never been demonstrated. (The human is a "dead end" host.) It is impossible for one person to catch it directly from an infected person.
Symptoms of West Nile Fever: The vast majority of human cases (perhaps as many as 99%) are subclinical, demonstrating no signs or symptoms. A small minority may notice "flu-like" symptoms of fever, achiness, fatigue, etc. In a much smaller fraction of persons, especially those with weakened immune systems (the elderly, very young, immunosuppressed, etc) the disease can progress to inflammation and swelling of the brain, a life threatening condition termed encephalitis.
Symptoms of encephalitis include high fever, neck stiffness, muscle weakness, disorientation, tremors, convulsions, and worse. Anyone who has these symptoms should see a physician immediately. As for viral diseases in general, there is no cure, and supportive measures are the best that can be offered at this time. There is an excellent review of the topic at the CDC site on West Nile Virus .
The frequency of cases of West Nile Fever should decline with time. As more individuals are infected and become immune to the virus, the number of acute cases will decline in proportion to those as of yet uninfected. (In parts of Africa, the number of immune individuals in the population approaches 100%.) Thus in a few years, West Nile Fever, although endemic, is expected to decline in frequency.
The Asian Tiger Mosquito (Aedes albopictus) is an aggressive mosquito which has been spreading through the United States since its importation in 1985 in a load of used truck tires shipped from Japan to Texas. It was first reported in Hamilton County, Ohio in 1996, but according to the CDC, was not seen in Clermont County until 1999 when I discovered one flying about in my office at the University of Cincinnati Clermont College. Below are three views I took of this species (in my office). I have received confirmation from the CDC that this is indeed Aedes albopictus. Evidence of its increasing prevalence in Clermont County was noted 30 April 2001 during a Biology Field Hike along the East Fork of the Little Miami (in Sycamore Park, Batavia, Ohio) when one of my students, Esther Anders (on the far right of the picture), spotted it biting her and asked "Isn't this one of your Tiger Mosquitoes?" I caught it and the photograph I took of it confirms that it is indeed Aedes albopictus . On 7 September 2001, I observed Aedes albopictus freshly emerged from a plant catch basin at my home in SW Clermont. The two pictures at the top of the page were taken of it then. Since that time, neighbors and students report sightings with some regularity. It is well established in Southwestern Ohio as of August 2002.
DISEASES IT CAN SPREAD: This mosquito is known to be an effective vector for a variety of diseases including Yellow Fever, Dengue Fever, and numerous of types of encephalitis, including LaCross encephalitis (which triggered an epidemic in West Virginia in recent years). Most recently, with heightened concern about West Nile Virus epidemic in the Eastern United States (see box above) it is notable that this species of mosquito has been shown to have the ability to harbor the virus.
BREEDING AND BITING HABITS: It is an unusual mosquito in a number of ways, none of them endearing. It lays its eggs in small cavities, including discarded drink cans, gluing the eggs to the inside above the water level. The eggs remain dormant until rains raise the water above the eggs, which then hatch. They can produce numerous broods in a short time, and are very aggressive biters, flying straight in and biting immediately rather than buzzing around, which could give time for a protective swat.
HOW TO RECOGNIZE IT: It is relatively easy for even the novice to recognize. It has black legs with striking white "spots" on them ("checkered legs"), and it hold its hind legs in the air. It has a diagnostic white "racing stripe" down the top of its thorax.
Additional pictures of Ae. albopictus, most of which I have taken, may be found in this directory .
In this first picture which I took in my office (as it bit me...), the diagnostic white "racing stripe" on top of its thorax is clearly visible:
In this picture, also taken in my office, note the black and white
hind legs held in the air, and the "ornamented" thorax and abdomen.
Here is a "front view" of the specimen in my office, having landed
one of my plants.
It shows the diagnostic "racing stripe" on the thorax very well.
Below is the CDC map which charts the spread of the Asian Tiger
from Houston, Texas in 1985, throughout the South and along the Eastern
seaboard. You will note that Hamilton County, the
county in Ohio, recorded this species of mosquito in 1993-94, but
County, just to the East of Hamilton County, has never (as of 1997)
the species until now.
Here is a jpeg from the web showing an excellent view of Aedes albopictus taking a blood meal. Notice the "Racing Stripe" on top of its thorax, and the black and white stripes on its hind legs.
LINKS: Here are a few links to other mosquito pages:
State Entomology Page . Excellent page on mosquito biology
differentiating A. albopictus eggs, larvae and adults from
This is an article describing Aedes albopictus' ability to transmit LaCross encephalitis . Many good bibliographic references.
Page on A. albopictus from University of Virginia , lists some of diseases spread by this species.