Synanthropic Fly Problems

Synanthropic flies are those that enter and adapt to the human ecological community. The unsanitary habits of man cause this relationship to develop. Increases in the fly populations may be expected after natural disasters, because of breakdown of sanitary services. The presence of synanthropic flies has potential epidemiological and hygienic implications, and the flies are an annoyance interfering with human comfort. The house fly, Musca domestica, is both a filth feeder and breeder, and health problems can occur when it comes into contact with human food and drink. The contamination of food and drink by pathogens can take place mechanically, through its legs, body, proboscis and wings.

The pathogens can also be defecated or regurgitated. Flies have been incriminated in the transmission of many of the enteric diseases of man, including dysenteries, cholera and typhoid fever. Yaws, conjunctivitis, enteroviral infections, and intestinal parasites may be transmitted by different species of flies.

Female house flies oviposit in a number of habitats, especially in garbage and animal wastes. When the average outside temperature is between 25° and 30°C, the life cycle of the fly from egg to adult, is approximately one to two weeks.

Surveillance and Survey Methods

Active fly control is not often included in most health programs. The first indication of a fly problem may be that of complaints from people living in refugee areas or who return to their homes in the disaster areas.

There are a number of fly traps, such as sticky paper, that can be used to appraise population densities. Not all synanthropic flies, however, enter houses and thus, markets, garbage areas, and even outdoor resting places have to be included as areas of appraisal. The easiest way of performing a survey is to count flies as they rest on refuse, vegetation, the walls of buildings and other resting places. Comparable information can be obtained with fly grills. (Ann. Rev. Ent. l: 323-346).

There are a number of other diseases of which rodents may be reservoirs. These include rabies, rat bite fever, rickettsial pox, spotted fevers, and rodent associated viral hemorrhagic fevers. For any rodent-borne disease problem, it is essential to determine if the disease is or recently has been in the disaster area. Since many of these diseases are associated with ectoparasites of the reservoir, it is important to know the natural histories of the diseases and to implement an appropriate control program against rodents and their ectoparasites.

Control and Evaluation

Prevention is recommended over control. High priority should be placed on sanitary services in refugee camps because of crowding and other unhealthy conditions. Sanitary services should also be restored to communities as soon as it is possible. Dead animals should be immediately cremated or buried, pit latrines should be made flyproof, and the rooms in refugee buildings, particularly kitchens and eating places, should be screened.

The public should receive health education about ways to prevent fly breeding. Other activities to recommend include burying garbage when sanitary services are not available, and using fabric curtains at doors and windows to limit fly entry. When available, the use of sticky tapes and household aerosol sprays inside of buildings may help to reduce fly numbers.

Chemical control of filth flies over a long period of time is usually not recommended because their resistance to insecticides develops rapidly and is already widespread. During disasters, however, it may be necessary. Residual spraying of indoor resting places may be required and, if available, sugar and syrup baits with insecticides can be utilized once the sanitary program is well underway. Use of diesel oil in pit latrines is a quite effective control measure. Space spraying resting and breeding places with available insecticides (those used for malaria and anti Aedes aegypti programs) can help to reduce fly numbers.

Evaluation may be largely based on direct observation. If an insecticide is not causing an appropriate level of mortality, an alternative should be used. Walking through an area, especially around pit latrines, food preparation areas and garbage collection sites, provides a means of visually assessing the reduction of the population. In control operations, it should be taken into account that flies can migrate up to four miles to new food attractants or to breeding areas. More accurate information may be obtained through the use of standardized fly grill surveys.