How The Us Deals With

Filaria

THE spread of filariasis (which is a curse in Eastern Polynesia) can be greatly curtailed by spraying mosquito-infested houses and schools with DDT, according to the United States Public Health Service. The conclusion is based on a 21-months’ programme of DDT spraying at St. Croix in the Virgin Islands—the first comprehensive DDT spraying programme ever inaugurated against the type of mosquito that carries filariasis throughout many tropical countries.

Use of DDT as a residual spray alone will not eradicate this disease-carrying mosquito, for the mosquitoes apparently can live long enough to perpetuate their species. But an adult mosquito cannot live long enough in a DDT atmosphere for the filariasis worms it carries to de velop to the stage where they will infect human beings.

The spraying programme was begun at St. Croix in 1946, as -a co-operative project of the Public Health Service, the School of Public Healtih of Columbia University (New York) and the Muni cipal Health Department of St. Croix.

Preliminary surveys had revealed that the chief breeding places of the mos quitoes were not swamps (except at the height of the rainy season), but in arti ficial containers—tins, cans, cisterns and water barrels, and in polluted water usually found near human habitations.

During the first treatment all build ings were sprayed. In subsequent spray ings only occupied houses and schools were treated. Experience showed that a 25 per cent. DDT-Xylene-Triton con centrate was the most effective.

At the end of 21 months, investigators found that half the buildings that had been sprayed were completely free of mosquitoes. The number of mosquitoes containing filariasis worms had been re duced by about half. No mosquitoes con taining worms that had reached the in fectious stage were found.

It proved more difficult for researchers to assess the reduction in filariasis in humans since the disease is not discern able in the human blood stream for about a year after infection. The general in dications seemed to be, however, that the rate of infection had been greatly re duced by the spray programme.

Other effects of the spray programme were the complete elimination of the type of mosquito that transmits yellow fever, and of fleas, bed-bugs and roaches. —United States Information Service.