Visceral leishmaniasis (VL) is a systemic protozoan disease that is transmitted by phlebotomine sandflies. Poor and neglected populations in East Africa and the Indian sub-continent are particularly affected. Early and accurate diagnosis and treatment remain key components of VL control. In addition to improved diagnostic tests, accurate and simple tests are needed to identify treatment failures. Miltefosine, paromomycin and liposomal amphotericin B are gradually replacing pentavalent antimonials and conventional amphotericin B as the preferred treatments in some regions, but in other areas these drugs are still being evaluated in both mono- and combination therapies. New diagnostic tools and new treatment strategies will only have an impact if they are made widely available to patients.

http://www.bio.umass.edu/micro/klingbeil/590s/Reading/Leishdiag2007.pdf

Visceral leishmaniasis: what are the needs for diagnosis, treatment and control?

Leishmaniasis is a deadly vector-borne disease that causes significant morbidity and mortality in Africa, Asia, Latin America and Mediterranean regions. The causative agent of leishmaniasis is transmitted from man to man by a tiny insect called sandfly. Approximately, 600 species of sandflies are known but only 10% of these act as disease vectors. Further, only 30 species of these are important from public health point. Fauna of Indian sub-zone is represented by 46 species, of these, 11 belong to Phlebotomine species and 35 to Sergentomyia species. Phlebotomus argentipes is the proven vector of kala-azar or visceral leishmaniasis in India. This review gives an insight into the insect vectors of human leishmaniasis, their geographical distribution, recent taxonomic classification, habitat, and different control measures including indoor residual spraying (IRS), insecticide-treated bednets (ITNs), environmental management, biological control, and emerging resistance to DDT. Role of satellite remote sensing for early prediction of the disease by identifying the sandflygenic conditions cannot be undermined. The article also underlines the importance of synthetic pheromones which can be used in near future for the control of these vectors.

/pdf/insect-vectors-of-leishmania-distribution-physiology-and-34pzpqtipd.pdf

Insect vectors of Leishmania: distribution, physiology and their control.

Indoor residual spraying is a simple and cost effective method of controlling endophilic vectors and DDT remains the insecticide of choice for the control of leishmaniasis. However resistance to insecticide is likely to become more widespread in the population especially in those areas in which insecticide has been used for years. In this context use of slow release emulsified suspension (SRES) may be the best substitute. In this review spraying frequencies of DDT and new schedule of spray have been discussed. Role of biological control and environment management in the control of leishmaniasis has been emphasized. Allethrin (coil) 0.1 and 1.6 per cent prallethrin (liquid) have been found to be effective repellents against Phlebotomus argentipes, the vector of Indian kalaazar. Insecticide impregnated bednets is another area which requires further research on priority basis for the control of leishmaniasis. Role of satellite remote sensing for early prediction of disease by identifying the sandflygenic conditions cannot be undermined. In future synthetic pheromons can be exploited in the control of leishmaniasis.

Vector control in leishmaniasis.

Visceral leishmaniasis (VL) is a deadly vector-borne disease that causes an estimated 500 000 new cases a year. In India, Nepal and Bangladesh, VL is caused by Leishmania donovani, which is transmitted from man to man by the sandfly Phlebotomus argentipes. In 2005, these three countries signed a memorandum of understanding to eliminate VL from the region. Integrated vector management is one of the pillars of this elimination strategy, alongside early case detection and treatment. We reviewed the evidence of effectiveness of different vector control methods, to examine the potential role of insecticide treated bednets (ITNs). Indoor residual spraying has shown poor impact for various reasons and resistance to DDT is emerging in Bihar. Environmental management performed poorly compared to insecticide based methods. ITNs could give individual protection but this still needs to be proven in randomized trials. Given the constraints of indoor residual spraying, it is worthwhile to further explore the use of ITNs, in particular long lasting ITNs, as an additional tool in the VL elimination initiative.

/pdf/vector-control-by-insecticide-treated-nets-in-the-fight-hf2v0vjq4c.pdf

Vector control by insecticide-treated nets in the fight against visceral leishmaniasis in the Indian subcontinent, what is the evidence?

Conventional methodologies to control vector borne diseases with chemical pesticides are often associated with environmental toxicity, adverse effects on human health and the emergence of insect resistance. In the paratransgenic strategy, symbiotic or commensal microbes of host insects are transformed to express gene products that interfere with pathogen transmission. These genetically altered microbes are re-introduced back to the insect where expression of the engineered molecules decreases the host's ability to transmit the pathogen. We have successfully utilized this strategy to reduce carriage rates of Trypanosoma cruzi, the causative agent of Chagas disease, in the triatomine bug, Rhodnius prolixus, and are currently developing this methodology to control the transmission of Leishmania donovani by the sand fly Phlebotomus argentipes. Several effector molecules, including antimicrobial peptides and highly specific single chain antibodies, are currently being explored for their anti-parasite activities in these two systems. In preparation for eventual field use, we are actively engaged in risk assessment studies addressing the issue of horizontal gene transfer from the modified bacteria to environmental microbes.

/pdf/paratransgenic-control-of-vector-borne-diseases-4hbg6arn18.pdf

Paratransgenic Control of Vector Borne Diseases

Editor – Vector resistance to insecticides has been highlighted by Kasap et al. in their comparative study relating to malaria in Turkey (1). In India, phlebotomine sandflies used to be considered highly susceptible to all insecticides; but indiscriminate use poses a problem of resistance, for example, in Bihar, where spraying with DDT has continued since 1976 (2). Resistance to DDT in Phlebotomus argentipes, a proven vector of Kala-azar in India, was reported for the first time in a village of Samastipur district (3). We therefore undertook a study in seven villages in Patna, Darbhanga, Samastipur, and Vaishali districts to ascertain the present trend of susceptibility of sandflies to DDT spraying in endemic areas of Bihar. Batches of 15–20 bloodfed and active half-gravid female adult sandflies were collected in the early morning by torchlight, with aspirators, and exposed toDDT4% for one hour. Their susceptibility status was determined by the WHO test kit, and mortality was recorded after 24 hours. All the sandflies dead or alive were identified (4). The temperature and humidity were maintained at 24+2 C and 75%, respectively. A village in Patna district, where no DDT spraying had been carried out for 25 years, was selected as a control. Effectiveness of the insecticide was found to be 100% in Patna and Samastipur districts. In Paswantola and Chakkatola villages (Darbhanga district) and Dakshinitola village (Vaishili district), vector mortality was 98.24%, 96.28% and 97.57%, respectively, whereas in another village in Vaishali (Ravidastola) susceptibility was 78.5% in 1998 and 71.42% in 1999. Our observations indicate that the leishmaniasis vector Ph. argentipes has developed resistance to DDT in an area of Bihar, in line with findings reported from Samstipur district (3). Further study is therefore required in endemic areas. n Ram Singh, Assistant Director R.K. Das, Chief Medical Officer S.K. Sharma, Joint Director Kala-azar Unit National Institude of Communicable Diseases, Patna 800 013, India

/pdf/resistance-of-sandflies-to-ddt-in-kala-azar-endemic-2de6akftek.pdf

Saurabh Sharma

Papers

Resistance of sandflies to DDT in Kala-azar endemic districts of Bihar, India