female mosquito finds you by following signals given off by your body such as
body heat, odors and carbon dioxide. Light and movement also help her zero-in
on you. She then sinks her long and thin mouth parts into your skin and sucks
out a drop of blood, engorging so much that she can barely fly away. During
the biting process, she secretes saliva into the cut to prevent the blood from
coagulating. Your bodys reaction to this saliva is what causes the bite
to itch and swell.
Mosquitoes can carry two diseases in American Samoa: filariasis and dengue.
Both can cause serious problems. These diseases are spread by specific mosquito
species: dengue (principally Aedes polynesiensis and Ae. aegypti)
and filariasis (mainly Aedes polynesiensis, and Oc. samoanus).
Filariasis, also known as elephantiasis (tutupa, mumu), is caused by
parasitic nematode worms called filariae. When an infected mosquito bites you,
these minute worms crawl from the mosquitos mouthparts onto your body
and into the cut. This is not a particularly efficient way to enter your body,
so the number of them transmitted from a single mosquito bite is probably limited.
Multiple mosquito bites by infected A. polynesiensis may be needed before
a person develops the full-blown disease. The worms lodge in a persons
lymphatic system where they can live for 4-6 years and produce millions of minute
larvae (microfilariae). These larvae circulate in your blood and are sucked
up by other
mosquitoes that bite you and thus can be spread to other people. In severe cases,
filariasis can cause a very large swelling of arms, legs or genitals.
The number of people infected in American Samoa is considerable. In two surveys,
people in several villages here were examined for filariasis and 17% (in 1999)
and 13% (in 2002) were found to be currently or recently infected. But not all
these people have swollen limbs. In general, about half of the people who are
infected show no symptoms of the disease, but they may develop them as they
get older. Our local Public Health Department together with the Center for Disease
Control has joined a
worldwide program to reduce filariasis by giving every person on island a medication
that kills the microfilariae circulating in your blood, thus preventing their
further spread by mosquitoes. The cycle of infection can be broken if the number
of people carrying this disease is significantly reduced.
key point to emphasize here is that filariasis and dengue cannot be spread directly
from person to person. An intermediate host, the mosquito, is required to transmit
Three other mosquito-borne diseases are worth mentioning. The most serious one,
malaria, does not occur in American Samoa. It is found in the western region
of the South Pacific, but the particular species of mosquito that transmits
malaria (the Anopheles mosquito) does not occur this far east.
fever is also transmitted by mosquitoes. Dengue is a viral disease that is rapidly
expanding in tropical and subtropical areas of the world. Its not native
to American Samoa but is periodically brought here by travelers from other infected
areas. It then gets spread around primarily by the daytimebiting Aedes polynesiensis
and Ae. aegypti mosquitoes. This virus is present in the mosquitos saliva,
so it is injected directly into you when an infected mosquito bites you. Symptoms
range from mild fevers to severe and potentially life-threatening illness. No
vaccine is available yet.
different type of malaria does occur here, but it infects only birds (avian
malaria). The birds dont seem to be greatly affected by it however, perhaps
because theyve adapted to it over a long period of time. Similarly, there
is a mosquito-borne parasitic nematode on island that affects dogs (heartworm).
tourists to American Samoa pick up these diseases? Not too likely. First, dengue
is usually not present here, only when an infected traveler brings the disease
here. Second, filariasis probably requires multiple bites by specific mosquito
species, and probably only a small percent of this species actually carries
the disease at any given time.
Scientists predict that we may see an increase in such diseases due to global
warming and climate change. Although exact mechanisms are not known, many pathogens
are sensitive to temperature; for example, growth, reproduction, and biting
rates of insects all increase with higher temperatures. Global warming appears
to be triggering a number of disease epidemics worldwide, involving a diversity
of pathogens (viruses, bacteria, fungi, parasites) and a wide range of hosts
(humans, corals, oysters, terrestrial plants, birds).
There are several basic measures that can be taken to reduce mosquito-borne
Find their breeding sites. Mosquitoes require water to complete their life
cycle, so removing pockets of standing water around your house will help reduce
their numbers. Survey your yard and eliminate areas where water can collect,
such as discarded tires, buckets, coconut shells, saimin bowls, aluminum cans,
cemetery urns, clogged roof gutters, etc. Drill holes in the bottom of large
containers so that the water does not accumulate in them, or cover large objects
like rain barrels with screening.
2. Avoid getting bitten. When the mosquitoes are out, wear long-sleeved
shirts and long-pants. Use repellants and insecticides safely. Repair window
screens on your house, and if needed, sleep under mosquito net tents while resting
during the day and night.
3. Take filariasis medicine. Remember, you can be infected with the filariasis
worm and not have symptoms. The filariasis medicine is free, so take it every
year to break the cycle. If the health workers miss coming to your house each
year, go to the hospital and ask for the medicine.
4. Be thankful for the swiftlets (peapea). They eat mosquitoes
(and other flying insects).
may play a role in the grand scheme of things, but Im not really keen
on the idea that they want to suck my blood. Worse still, they can infect us
with two diseases in American Samoa -- more about that shortly. At least 12
species of mosquitoes (namu) occur in American Samoa. Most are common
across the western South Pacific region, but some are endemic to the Samoan
islands (Aedes upolensis, Coquillettidia samoaensis, Ochlerotatus samoanus,
Oc. tutuilae) and a few are newly introduced. Their life cycle involves
several stages, one is the irritating adult mosquito, but their juveniles live
in water. To reproduce, the adult female needs to obtain a blood meal (from
you) to develop her eggs. She then lays her eggs in quiet puddles of water where
they hatch and grow. The larvae breath air, so they generally hang around at
the water surface but will wiggle quite actively when disturbed. After a week
or two, the larvae pupate (a resting stage) and then emerge as flying adults.
Females may live for 2-3 weeks and lay several clutches of eggs (each requires
a blood meal). Only the female mosquito searches for a blood meal; the males
(the ones with fuzzy
antennae) feed on plant nectar. Also, not all the mosquitoes are after you personally
-- some species seek out birds as their preferred blood meal.
Filariasis & Dengue Fever