Tuesday, April 22, 2008

Mosquitoes, Malaria, and Walter Reed

In Georgetown, S.C., the humidity is high and the heat is intense.' Add to this climate billowing clouds of mosquitoes and there could be no worse environment to live in.

The people in Georgetown are well-adapted to the ways of mosquito control.'' Georgetonians dare not venture outside without a thorough dousing of Avon's Skin-so-Soft moisturizer (for gnats) or Deep Woods Off (for mosquitoes). Georgetonians know to empty rain-filled containers, which can service as mosquito breeding ground.' At night, there is a purple pall cast over the town from so many outdoor lights'bug lights that attract mosquitoes and then kill them with a jolt of electricity.

In Georgetown, the truck that sprays Malathion fog is as common as the garbage truck in other parts of America.' This city is only one of many fronts against the most infamous of insects: the mosquito.

People wage war against mosquitoes in order to eliminate the deadly diseases that mosquitoes carry.' People blessed by living in areas of the world where the threat of vector-borne diseases is not constant tend to lose sight of the severity of the problem.' However, the threat is still there.

Yellow fever'also known as Black Vomit for the violence of its symptoms'is one disease spread by mosquitoes. Another is encephalitis, a virus that can attack the brain, causing it to swell.

Several types of nematodes that causes diseases are carried by mosquitoes.' One such disease is elephantiasis. Which can distort the functions of the lymph glands and cause limbs to become grotesquely swollen.' Another is heart-worm disease which infects dogs with worms up to three feet in length.

The number one vector-borne disease affecting humans in malaria.' This widely known infection causes 105 degree fevers that appear and reappear in successive waves.' Although estimates very greatly, Africa News reports that malaria infects 270 million people and kills 1.5 million each year.' Eighty-five percent of all malaria deaths occur in Africa.' Virtually all 1,100 cases reported in the United States last year were contracted abroad.

The Link to Malaria

Scholars long ago speculated that mosquitoes spread disease but no one knew for certain that mosquitoes spread malaria until it was demonstrated by Englishman Dr. Ronald Ross in 1898.' For his work, Dr. Ross won the Nobel Prize.' When he published his proof, Dr. Ross referred to a dappled-wing mosquito.' Now we know that malaria is spread by the Anopheles mosquito.

Working in India, Dr. Ross watched through a microscope the mechanism through which mosquitoes spread malaria.' Mosquitoes ingest male and female gametocytes. These reproduce, creating zygotes that live in the lining of the mosquito's stomach.

The zygotes change in nine or ten days into oocysts, travel through the mosquito's body, and come to rest in the head.' At maturity, the oocysts become sporozites which are injected into the next hapless victim.

Once inside the body, the sporozites travel to the liver where they multiply.' Now called merozoites, they invade red blood cells, multiple again, and ultimately cause these cells to burst.' When the parasites have reached sufficient density in the blood, the victim suffers violent fevers and spasms.

Malaria is not often fatal, unless the parasite is plasmodium falciparium.' This parasite not only bursts red blood cells, but it also makes them sticky.' The sticky blood can cause a coma.

Antimalarial Drugs

The traditional method for controlling malaria is quinine, a substance extracted from the bark of the cinchona tree.' A project is currently underway in The Netherlands to test a 2,000-year-old Chinese remedy made from the quinghao plant.

Chloroquine is another chemical used to treat malaria.' Unfortunately, the malaria parasite can become immune to the treatment.' The British magazine Nature reported in 1992 that scientists have studied chloroquine more closely and have discovered exactly how chloroquine attacks the malaria parasite.' Scienists might be able to synthesize a replacement.

Cuba and Panama

In 1899, after the Americans occupied Cuba during the Spanish-American War, Dr. Walter Reed traveled to Havana to combat yellow fever.' Using brave volunteers, Dr. Reed demonstrated that yellow fever could only be spread by the Aedes aegypti mosquito.

To rid the island of Aedes aegypti, households in Havana were ordered to dump ever container of water of pay a $10 fine.' Cleanup squads fumigated houses, drained swamps, and poured oil into ditches.' By 1902, yellow fever was eliminated from Cuba.

The Panama Canal could not have been built had not the mosquitoes been eradicated by Dr. William Crawford Gorgas.' The United States spent $3.50 on every one of the 100,000 workers in the Panama Canal Zone to rid mosquitoes from a 100-square mile strip of land.' Yellow fever was eliminated by 1906.' The incidence of malaria was reduced from 800 out of every 1,000 workers in 1906 to 16 out of 1,000 in 1916.

Prior to the American effort, the French tried and failed to build the canal.' To demonstrate the healthy environment of the Canal Zone to would-be workers, in 1883 a French project directed moved his family from France.' Within one year, his wife, son, daughter and her finac饼/span> were dead from yellow fever.

Past Control Efforts

To eliminate malaria or yellow fever from an area, it is not necessary to eliminate all the mosquitoes'it is only necessary to kill a sufficient number.' The World Health Organization knows this fact and has abandoned eradication as a goal of mosquito control.

A complete elimination of mosquitoes is not possible because mosquitoes are extremely prolific.'' If you eliminated most of the mosquitoes in an area, but not every single one, their large numbers would eventually return.

This fact was realized only after much effort.' Some of the earliest work at the philanthropic Rockefeller Institute was directed toward eradication of the Anopheles and Aedes aegypti mosquitoes.' With a budget of several hundred thousand dollars, and many thousands of workers, its scientists literally coated the island of Sardinia with DDT (dicholoro-diphenyl-trichlorethane) shortly after World War II.' Disease was wiped out, but the mosquitoes were not.

Early efforts at mosquito control were largely the same throughout the world.' People were encouraged'often under the threat of civil fine'to empty containers of water near their houses.' Marshes were drained where possible, especially as part of land reclamation projects in such places as Italy.' Oil was poured onto stagnant water to suffocate the mosquito larvae.' In Greece, when petroleum became too expensive, olive oil was used.' Everywhere, screens were installed on windows.

Certain governments though malaria could be controlled by administration of guanine to the populace.' In Italy and Greece, state-run monopolies were set up to administer this treatment.

Early larvicides included Paris Green (aceto-arsenite).' Paris Green was cheaper than oil and did not hurt people.' It was not toxic to cattle nor fish.' Paris Green worked because it was exactly the right size to be eaten by mosquito larva.' Paris Green was used in Brazil to eradicate yellow fever in the mid-1940s.

DDT was by far the most effective chemical used to control mosquitoes. ''DDT doubtless saved millions of lives during World War II.' Because of the detrimental effect of DDT on falcons, sea lions, fish, and other creatures, DDD is not banned in most, but not all, countries.

Other Mosquitoes

According to Matt Yates, president of the American Mosquito Control Association, there is a new menace called Aedes albopticus, the Asian tiger mosquito.' The mosquito'first discovered in the United States in 1985 in Houston, Texas'is considered to be a competent vector of yellow fever, and therefore, can bring jungle yellow fever to urban areas.' In addition, this mosquito may spread encephalitis.

Culex pipens is another nuisance.' This mosquito can be dangerous, particularly in Florida, because is spreads St. Louis encephalitis.' Culex pipens is also a threat to dogs because of heart worms.

The California salt marsh mosquito, Aedes squimiger, an important human pest in coastal California, was previously not suspected to be a vector of human pathogens.' However, recent research fingers this pest as a new vector of California encephalitis.' In addition, the Pacific coastal states are threatened by the Jamestown Canyon virus, which was isolated in three species of snowpool mosquitoes.


Because malaria and yellow fever are no longer prevalent in the United States, they are not a topic of concern to the general public.' However, the United States is still vulnerable to vector-borne diseases.

According to entomologist Jimmy K. Olson, Ph.D., priorities within the U.S. Health Service over the last two decades have shifted to cancer and AIDS.' The responsibility for managing vector-borne diseases has increasingly fallen to state and local public health agencies.' However, budget cuts and inflation have taken their toll on the ability of state and local agencies to maintain effective vector control programs.' Olson believes it is up to public educators and specialists involved in the prevention and control of vector-borne diseases to raise the public's awareness and support for this vital service.

Meanwhile, in picturesque Georgetown, S.C., the mosquitoes are as bad as ever.' But the natives do not mind the mosquitoes much.' 'It keeps the tourists away,' they say.

(This article was published in Pest Management Magazine in April 1992.)

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