Detection & treatment of microfilaria carriers and recurrent anti mosquito measures.
How can the menace of filariasis be controlled?
Filariasis can be controlled by employing measures to eliminate the parasite in humans as well as the vectors. DEC (Diethyl Carbamazine) is a drug which is effective in the treatment of filariasis. DEC is still the only drug available for chemotherapeutic control of filariasis. The administration of DEC can be carried out in various ways:
Mass administration to all persons in the community irrespective of whether they had filariasis, was tried in the late 1950s and met with little success. It is an expensive approach and relies on the people to take the medicine, and non–compliance was one of the reasons for failure. It also requires intensive health education of the general public. Currently, the approach is based on detection and treatment of human carriers and filarial cases. The recommended dose in the Indian program is 6 mg DEC per kg of body weight daily for 12 doses, to be completed in two weeks (i.e. six days a week). In endemic areas, treatment must be repeated at specified intervals, usually every two years.
Addition of DEC to salt for mass treatment
This strategy has been tried in the Island of Lakshwadeep and has been quite successful. It is also a cheap and safe method. Common salt medicated with 1–4 g of DEC per kg.
Mosquito control measures
This is achieved by spraying insecticides (anti–larval oils or organophosphates) which are lethal to the larvae of the mosquitoes. This strategy is largely done in the urban areas in India.
Environmental issues in the control of filariasis
The filariasis problem largely arises as a result of poor sanitation and hygiene. The emphasis should be on improving existing sanitary conditions. In the case of Mansonia mosquitoes, breeding is best controlled by removing supporting aquatic vegetation such as the Pistia plant from all water collections and converting the ponds to fish or lotus culture. Alternatively, certain herbicides such as phenoxylene 30 or Shell Weed Killer D may be used to destroy aquatic vegetation. Larvicidal operations are complemented activities such as filling up of ditches and cesspools, drainage of stagnant water, adequate maintenance of septic tanks and soakage pits etc.
Firstly, in order to control the disease, an estimate of the problem by conducting surveys has to be undertaken. In India, the NICD (National Institute of Communicable Diseases, Delhi) conducts a filarial survey. There are many elements in the survey. The survey can either entail the examination of patients for the symptoms of filariasis, or the examination of blood samples, particularly at night time to demonstrate the parasite. Many times, the parasite is difficult to detect in the blood, and tests which measure antibodies against the parasite may have to be employed.
The finding of the parasite in the mosquito can be done by allowing mosquitoes to feed on the patient, and then dissected two weeks later. Where other techniques may fail, this may succeed in detecting low density microfilaremia.
This comprises general mosquito collection from houses, dissection of female vector species for detection of developmental forms of the parasite, a study of the extent and type of breeding places. The data is assembled, analyzed and used for the compilation of certain filarial statistics. There are three reasons why filariasis never causes explosive epidemics:
- The parasite does not multiply in the insect vector.
- The infective larvae do not multiply in the human host.
- The life cycle of the parasite is relatively long, 15 years or more. These factors favor the success of a control program.