| Control and prevention of visceral leishmanisis (Kala-azar) |
Visceral leishmaniasis (Kala-azar) is a vector born disease. Phelebotomus argentipes is the vector of Indian Kala-azar. Visceral leishmaniasis (VL) or kala-azar resurged as a serious public health problem in the country since 1970’s in the state of Bihar and later spread to West Bengal and Eastern Utter Prades.
Sand flies are small in size about 1/3rd of the size of mosquito. They have large conspicuous eyes on their body. Body is covered with hairs. Hind legs are longer than the body. Wings are kept erect (About 60 degrees angle to the body surface) and parallel to each other when the adult fly is in resting position. The species of males can be distinguished mainly by length and relative lengths of coxite and style. Also by number, size, position of spines on style and surstyle. Females can be differentiated by the shapes, length, and number of segmentations on the body/smooth and presence of long/ short neck of the spermathica. The position of the sandflies in the animal kingdom is as follows:
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| Animal Kingdom |
Invertebrata |
Phylum
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Arthropoda |
| Class |
Insecta |
| Sub-class |
Pteryogota |
| Order |
Diptera |
| Group |
Nematode |
| Family |
Psychodidae |
| Sub –family |
Phlebotominae |
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Out of about 700 species under 6 genera recorded in both New and Old world 11 species under genus phlebotomus and 35 confirmed /presumed vector species for visceral Leishmanisis (Kala-azar) is P. argentipes; for Cutaneous Leishmaniasis/ oriental sore P. papatasi, P. salehi, P.sergenti; and for snadfly fever P. papatasi. They all belong to genus Plebotomus.
Division of vector biology and control of the Institute is working mainly on the Vector Biology of “phlebotomine flies”. It has well equipped laboratory with two thermo-regulated insectorium for sandfly breeding and other experiments. At present the laboratory is maintaining ninth generation of Phlebotomus argentipes.
Division of vector Biology & Control is mainly concerned with the development of new strategies for the control of vector of kala-azar. Methods of vector (sandfly) control can be grouped as follows: |
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1.1-DDT- Still remains the insecticide of choice. Dosage schedule of 1 gm/m2 or 100 mg/ft 2. or 200 mg/ft2. has been found to be quite effective. It remains effective from 6-12 months. DDT as a suspension is the choice in 5% emulsified suspension.
1.2-Malathion: Evaluation of long acting paint formulation (slow release Emulsified Suspension,SRES) vs DDT was found effective for at least 2 years approx. following single spray. Serum cholinesterase level of exposed population remains within normal range after spray. The reports of resistance to DDT are being reported from several parts of Bihar and hence an attempt to DDT alternative has to be looked into. Since, malathion has already been used in several other parts of India for vector control purposes, it may be envisaged to introduce malathion as an alternative measure to see its efficacy as well as its toxicity if any, in control strategies programme here. No studies of Malathion spray has been made in Bihar state, which is at present highly endemic for Kala-azar on India. The data of spray men and exposed population are presented and discussed at different intervals of exposure to assess its efficacy as well as its side effects, if any, for its future implementation as an alternate effective anti Kala-azar vector measure in Bihar on large scale. Malathion Paint Formulation showed decrease in ChE level in the spray man just after exposure but no toxicity observed. The amount of reduction of mean ChE level is well within normal range. After exposure ChE level was found to be 82% of the normal ChE level of spray men and hence it is suggestive of no toxicity amongst spry men.Even exposedindividualsin the study areadid not reveal any level of ChE. After one and four week of exposure, the ChE level reduces by 21% and 18% respectively in exposed individuals. After one ear of rxposure the normal ChElevel retained by the exposed individuals. It indicates that malathion does not induces any long or short term toxicity with passage of time.
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Application of mud and lime plaster up to 1.22 meter in households of endemic foci was established as bioenvironmental control measure of vector. Due to the emerging problems of use of insecticide control, there is an increasing need to evaluate a mechanical method as vector control strategy against Kala-azar.One such mechanical method comprises of mud plastering of wall and crevices of the house with lime painting to stop sandfly breeding. It is a noble method known as techno-ecological control of sandflies. This does not require any extra labour, supervision or expensive material.
A pilot study was initiated at village Bhadwar in Bhojpur district, 45 Kms. west of Patna that has not been sprayed with any insecticide in recent past. The village had 108 houses of which 63 were made up of the mud and the remaining with brick and cement. There were 36 cattle sheds out of which 28 were made of mud. The rest eight houses were made up of and had holes and crevices on the walls. All the cattle sheds were in dilapidated condition providing favourite conditions for sandfly breeding. In the village 10 houses with roofed cattle sheds were randomly selected (7 cattle sheds were made up of mud and rest with bricks) as “test” houses. Five roofed and closed cattle sheds, which were separated from houses by approx.450 mts. were selected as “control”. Of 5 cattle sheds in the control group, 3 were made up of mud and 2 with bricks. Before the interventions initiated, P.argentipes were collected from households and per man-hour density of collection at intake phase determined.
The reduction of P.argentipes may be due to destruction of breeding sites and the larvicidal effects of lime. However, due to reappearance of crack and crevices on the wall after seven months, P.argentipes breeding might have build up and therefore PMH density increased in the month of July. Study result indicates that applications of such technique annually can assist vector control means for Kala-azar and these could be most cost-effective method that can be acceptable to the community.
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Biological methods: It has been observed during laboratory colonization of P. argentipes that particular type of unidentified mites growing at a prolific rate between 27-300C causes high degrees of larval mortality. Interestingly same types of mites were isolated from soil scraping in the field in which sandfly larvae/pupal exuviae have been detected. Attempts are being made to rear these mites in laboratory condition to see its effect on sandfly larvae. If the trial is successful, this can be a very useful tool for biological control. |
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Genetic methods: When eradication of vectors could theoretically be achieved by the release of insects through altered genetic characters into natural vector population. Genetic control can be done through the release of males/females from laboratory cultures with genetic characters. Coupling with mates from natural population results in production of non-viable progeny. No attempt has been made to control the sandflies through this seemingly ideal way of control. However successful application of a genetic method of sandfly control demands precise knowledge of the distribution of the target species and their bioeclogy.
A part from these conventional methods of sandfly control, feasibility of application of remote sensing for prediction of Kala-azar epidemic in selected foci in Bihar is being investigated. Sandfly distribution with relation to seasonal and spatial changes in land use/land cover variables in both endemic and non-endemic foci are being monitored and data generated for classification. Digital map is prepared for overlaying satellite data. Data generated in 4 test villages selected randomly in hyper- endemic Vaishali district and non-endemic Loharadagga district were compared. This will facilitate overlaying of remote sensing data for accurate observation and evaluation of index eco-epidemiological factors.
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