Mosquitoes and the Diseases they Carry

Nearly everyone has expe­ri­enced a mos­quito bite, the raised bump, the unbear­able itch­ing. The story of mos­qui­toes and man is a com­plex tale of adap­ta­tion, co-existence and far too often, a deadly illness.

The United States, and upstate New York, are very famil­iar with both mos­qui­toes and the ill­nesses they may carry. The ease with which the world inter­con­nects at this time is bring­ing some strangers to Amer­ica, new breeds of mos­quito and new illnesses.

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Not all mos­qui­toes bite humans. Some bite both ani­mals and humans. Some only bite humans. All bit­ing mos­qui­toes have one thing in com­mon, they’re female. The blood they draw when they bite allows them to repro­duce. The ill­nesses, viral, bac­te­r­ial and par­a­sitic, that they ingest from sick peo­ple and carry to other peo­ple, are just inci­den­tals to their main pur­pose. They want to make babies and they need our blood to do it.

WEST NILE VIRUS

Rochester and Upstate New York res­i­dents are famil­iar with the West Nile virus.  It arrived in the United States about 1999, and was first dis­cov­ered in New York City. While most peo­ple infected with the virus show no symp­toms, those with symp­toms suf­fer a flu-like ill­ness for days or weeks.  In less than one per­cent of those infected, life threat­en­ing forms of West Nile called West Nile encephali­tis, West Nile menin­gi­tis or West Nile menin­goen­cephali­tis can develop.

West Nile is spread by var­i­ous mem­bers of the Culex fam­ily of mos­qui­toes with C. pip­i­ens being the pri­mary car­rier in New York.  It is also called the North­ern House Mosquito.

C. pip­i­ens loves the filthy water around peo­ple.  It breeds in storm drains and sew­ers, even raw sewage and at sewage treat­ment plants.  It feeds on birds, some mam­mals and on humans.

YELLOW FEVER

New York has not seen a local out­break of yel­low fever since about 1870. Before then, the ill­ness was a reg­u­lar vis­i­tor to New York City, Albany and other parts of the state.

Aedes aegypti is the usual mos­quito car­rier of this ill­ness. Cur­rently it is found much far­ther south than New York, though its range varies with the weather.

A. aegypti is very adapted to liv­ing around humans.  It has reg­u­lated its wing speed to reduce the buzz or hum that humans iden­tify with mos­qui­toes. It is a day feeder, choos­ing the early morn­ing or late evening to feed. Dur­ing the heat of the day these mos­qui­toes seek out dark hid­ing places where there is lit­tle air cir­cu­la­tion, like clos­ets or under tables. Most bites from A. aegypti are to the lower leg.

A. aegypti is the oppo­site of the Culex mos­qui­toes when it comes to breed­ing sites. It seeks clean water, rain gut­ters, clear pools and con­tain­ers that have col­lected rain.

MALARIA

Malaria may be one of the ear­li­est ill­nesses to be described. It is a deadly ill­ness, killing about a mil­lion peo­ple world­wide every year. It was con­sid­ered elim­i­nated in the United States by 1951.

In New York, the malarial risk was along the water­ways, New York City, up the Hud­son River to Albany, along the Mohawk River west, the Lake Ontario and Lake Erie shorelines.

Malaria is a par­a­site car­ried and trans­mit­ted to humans by mos­qui­toes in the genus Anophe­les.  A.quadri­mac­u­la­tus is the vari­ety com­mon to the New York area.

Despite the erad­i­ca­tion of malaria in the United States, cases are dis­cov­ered every year.  Most are acquired by trav­el­ers in regions of the world where malaria is preva­lent.  There are occa­sional out­breaks, such as this one in New Jer­sey in 1991, that appear to be native.  It is almost cer­tain, how­ever, that the ini­tial host was a trav­eler who did not know they were sick and was bit­ten by mos­qui­toes.  This is a com­mon source of out­breaks of mos­quito borne ill­nesses not native to the United States.

A. quadri­mac­u­la­tus inhab­its the east­ern United States, east of the Mis­sis­sippi. They pre­fer fresh­wa­ter pods, steams and lakes with veg­e­ta­tion. The mos­quito prefers to take blood from ani­mals. They are night feeders.

DENGUE FEVER

Key West, Florida. The last out­break of this ill­ness native to the United States was in 1945, so its reemer­gence in 2009 was startling.

There have been dengue fever cases and out­breaks traced to trav­el­ers, includ­ing cases in Florida at this time. One traces to Puerto Rico, another to Haiti, both areas where dengue is endemic.

Dengue is car­ries by A. aegypti. This should mean that the out­break can only move as far north as this mos­quito can sur­vive, per­haps into the Car­oli­nas. How­ever, a recent ille­gal immi­grant to the United States may change that assumption.

A. albopic­tus, the Asian Tiger mos­quito, was acci­den­tally brought in to the United States in the 1980’s. It is known to spread dengue fever as well as east­ern equine encephalomyelitis and the Cache Val­ley virus. It is also reported to be able to carry West Nile.

The Aedes gen­era of mos­qui­toes are highly adapted to liv­ing near humans. they have also demon­strated a high degree of adap­ta­tion to chang­ing habi­tat. Their eggs may sur­vive for sev­eral months in a dried out area and revive when water returns to the area.

In an e-mail to me, Dr. Laura Har­ring­ton, Asso­ciate Pro­fes­sor, Depart­ment of Ento­mol­ogy at Cor­nell Uni­ver­sity, talked about the Asian Tiger mos­quito, A. albopic­tus.  She has found these mos­qui­toes in New York and New York City but they are not yet able to sur­vive year round.  This mosquito has the potential to be a vector for both existing disease and newly imported illnesses such as dengue fever.