Spying on Flies from the Skies

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http://www.hno.harvard.edu/gazette/1996/07.03/SpyingonFliesfr.html

 

 

 

Lyme disease is now a serious threat in the eastern U.S.; hantavirus

has spread from the Southwest into many states, and the

skin-ulcerating form of leishmaniasis has invaded south Texas.

 

 

 

 

Harvard University Gazette

 

 

Spying on Flies from the Skies

 

By William J. Cromie

 

Gazette Staff

 

Harvard scientists have launched a space war against bloodsucking sand

flies that carry a parasite which sickens and kills millions of people

each year.

 

With the help of satellites, they are predicting the most likely

places for outbreaks of leishmaniasis, a disease that infects an

estimated 12 million people worldwide. The same technology also has

been used to track the carriers of malaria, Lyme disease, cholera, and

other maladies.

 

A School of Public Health (SPH) team uses the method in Brazil to

blunt the " scourge of the tropics, " a virulent variety of

leishmaniasis that destroys internal organs. Flies transfer the

parasite to people, and the disease is fatal if left untreated.

 

" We're making encouraging progress in predicting where new outbreaks

of visceral leishmaniasis might occur, " says James Maguire, associate

professor of tropical public health.

 

The SPH effort concentrates in northeast Brazil, a " hot area " for the

disease. A major effort is ongoing in and near the city of Teresina,

which has a population of about 700,000 people and more than 57,000 dogs.

 

Dogs loom important in the cycle because they unwittingly act as a

storehouse, or reservoir, for the parasite. When an infected fly bites

a dog, it releases parasites into the canine at the same time that it

feeds on its blood. Uninfected flies that bite infected dogs can take

up the parasite and transfer it to humans.

 

Control measures include spraying pesticides and killing infected

dogs. As one might expect, the latter is highly unpopular. Many

infected dogs show no outward signs of infection, and officials have

trouble getting people to surrender their pets.

 

" These measures have been successful in keeping the overall number of

cases down, " Maguire notes. " But they don't eradicate the disease, nor

do they stop new outbreaks. One reason for this, we suspect, is the

existence of other reservoirs, specifically humans. If that's true, it

would make control programs much, much more difficult. "

 

Satellite Seeing

 

Even so, control is no picnic. The potentially deadly bites probably

occur inside or near houses. " We don't have the resources to examine

every house in a city of 700,000 people, " Maguire points out. " And we

don't know where sand flies breed, or their range of travel. "

 

To overcome those disadvantages, Maguire and his crew map the city and

its surroundings using images taken by U.S., Russian, and French

satellites. Neighborhood maps then are combined with information on

the type of vegetation, number of infections found, the quality of

houses, and socioeconomic conditions. Once areas at highest risk for

new outbreaks have been identified, protection efforts can be

concentrated there.

 

Satellite images turn out to be easier and cheaper to get than aerial

photos. " We can map a 13,700-square-mile area for less than $3,000, "

Maguire explains. " At present, the LANDSAT 5 satellite flies over

Teresina every 16 days. "

 

Seven sensors onboard LANDSAT give visual images as well as

information on heat and other ground radiation which can be used to

distinguish different types of vegetation. Images from Soviet spy

satellites make it possible to identify objects as small as a truck or

bus. Newer radar-equipped satellites, soon to be launched, will

provide photos even on overcast days and at night.

 

" So far, we've found an association between risk of infection,

closeness to vegetation, and density and quality of housing, " Maguire

says. " Squatter communities of closely packed, poorly constructed

houses, located near a forested corridor or an area of dense trees and

shrubs, offer an extremely high risk of leishmaniasis. A similar

density of better-built houses, where vegetation is cut back and

maintained, substantially decreases the risk. Leaf litter is the most

likely breeding place for the sand flies. "

 

SPH researchers are giving such information to authorities in

northeastern Brazil charged with fighting leishmaniasis. It will guide

their spraying and dog control measures to locations where they will

do the most good.

 

" Within the next six months, we expect to provide them with the kind

of data that will result in reduction of new outbreaks of the

disease, " Maguire says.

 

Treatments and Tests

 

Standard treatment for visceral leishmaniasis requires daily

injections of a compound containing the metal antimony, a treatment

with unpleasant side-effects including nausea, pain, and heart

irregularities. Each injection costs only $1, but in rural parts of

developing countries, the 20-day minimum treatment becomes

prohibitively expensive. And sometimes, the drug needs to be given for

40 or even 60 days.

 

John David, chair of the SPH Department of Tropical Public Health,

leads an effort to find better treatments, including a vaccine for

dogs. With more than 57,000 dogs in Teresina, vaccination would be a

monumental task without good data about where infections would most

likely occur.

 

David, the Richard Pearson Strong Professor of Tropical Public Health,

also has developed a field test to quickly screen dogs for leishmania

parasites.

 

" We can tell very quickly when a dog is infected, and removing

infected dogs seems to reduce cases of human leishmaniasis, " David

notes. " But we're still left with the problem of people hiding their

dogs because they don't want them killed. "

 

Experiments have also been done with humans. Carlos Costa, who

recently earned a doctor of science degree from the SPH, put 20

uninfected sand flies on the skin of leishmaniasis patients. More than

a third of them infected the flies, who could then, of course, infect

other humans. Studies in India reveal that humans are the sole

reservoir in that country.

 

" The question of whether dogs or humans are the main reservoir in

Brazil remains unanswered, " David admits.

 

Infected dogs get lethal injections; a solution impossible with

humans. If people serve as reservoirs but show no symptoms of the

disease, present control programs will never eradicate the disease.

For that, a more sensitive human test and a vaccine will be needed.

 

David and his colleagues also are evaluating a treatment for the

variety of leishmaniasis that attacks the skin. " Under anesthesia, a

probe applies 122 degrees of heat to a skin lesion for 30 seconds, " he

explains. " If it works, this would be a rapid way to treat the

disease, but we have yet to complete evaluation of this method in Brazil. "

 

The skin variety of leishmaniasis, which causes ugly sores on the

face, mouth, arms, and legs, occurs throughout Brazil's Amazon region.

The visceral leishmaniasis that attacks internal organs also occurs in

southern Europe, tropical Asia, and Africa. In Sudan, it's called " the

killing disease. " An estimated 400,000 people suffer from visceral

leishmaniasis worldwide, and it causes some 40,000 deaths each year.

Pinpointing the reservoirs and finding a better treatment, therefore,

could alleviate considerable suffering in the world.

 

While a vaccine would be specific to leishmaniasis, technology

combining satellite imagery and investigations on the ground could be

applied anywhere in the world to help control other infectious

diseases. It already is being used in various ways against Lyme

disease, malaria, cholera, hantavirus, and schistosomiasis, a tropical

disease that affects more than 200 million people worldwide. Lyme

disease is now a serious threat in the eastern U.S.; hantavirus has

spread from the Southwest into many states, and the skin-ulcerating

form of leishmaniasis has invaded south Texas.

 

" These health applications are just in the beginning phase, " Maguire

says. " Much more needs to be done. But we're very excited about

developing this technology to its full potential. "

 

Copyright 1998 President and Fellows of Harvard College