Can visceral leishmaniasis be eliminated from Asia?

Data on the burden of visceral leishmaniasis (VL) in Indian sub-continent are vital for elimination programme planners for estimating resource requirements, effective implementation and monitoring of elimination programme. In Indian sub-continent, about 200 million population is at risk of VL. Nearly 25,000-40,000 cases and 200-300 deaths are reported every year, but these are grossly underestimates. Recent well-designed multicentric studies identified VL burden of 21 cases/10,000 among sampled population in Indian sub-continent (Bangladesh, India and Nepal). This estimates 4,20,000 cases per 200 million risk population clearly indicating that the disease is highly under-reported. Chemical and environmental vector control studies show that the indoor residual spraying (IRS) and long-lasting insecticidal nets (LLINs) are effective and significantly reduce sandfly densities. The findings documented from different sources revealed that some gaps and weakness in existing policies for introducing VL vector control interventions. Our studies emphasize the need of integrated vector management with both IRS and LLIN vector control interventions. Active case detection with rK39 strip test as diagnostic tool is the key element for detection of VL cases. The use of oral drug miltefosine for the treatment after assessing feasibility at community level is important. Kala-azar elimination in Indian sub-continent is possible if elimination programmes ensure access to health care and prevention of kala-azar for people at risk with particular attention to the poorest and marginalized groups. The evidence-based policy should be designed that motivates to implement the programmes, which will be cost-effective. Maintaining the acceptable level of incidence requires public awareness, vector control, appropriate diagnosis and treatment. The five pillars of VL elimination strategies identified are: early diagnosis and complete treatment; integrated vector management and vector surveillance; effective disease surveillance through passive and active case detection; social mobilization and building partnerships; and clinical and operational research which need to be re-enforced to effective implementation.

Vector-control synergies, between 'roll back malaria' and the Global Programme to Eliminate Lymphatic Filariasis, in South-east Asia.

The problems of, and opportunities for the control of filarial vectors in the World Health Organization's South-east Asian Region are summarized and discussed. Together, the countries in this region have more than half of the world's burden of lymphatic filariasis (LF), most of it caused by Wuchereria bancrofti transmitted by Culex quinquefasciatus. Although the vectors and the epidemiology and distribution of LF in this area largely differ from those of malaria, some vector-control methods (such as bednets and other personal-protection measures, breeding-site reduction and environmental management) can have an impact on LF, malaria and other mosquito-borne diseases. Some of the relevant issues of programme management and integrated vector control are reviewed.

Cost-effectiveness and sustainability of lambdacyhalothrin-treated mosquito nets in comparison to DDT spraying for malaria control in western Thailand.

The cost-effectiveness of lambdacyhalothrin-treated nets in comparison with conventional DDT spraying for malaria control among migrant populations was evaluated in a malaria hyperendemic area along the Thai-Myanmar border. Ten hamlets of 243 houses with 948 inhabitants were given only treated nets. Twelve hamlets of 294 houses and 1,315 population were in the DDT area, and another 6 hamlets with 171 houses and 695 inhabitants were in the non-DDT-treated area. The impregnated net program was most cost-effective (US$1.54 per 1 case of prevented malaria). Spraying with DDT was more cost-effective than malaria surveillance alone ($1.87 versus $2.50 per 1 case of prevented malaria). These data suggest that personal protection measures with insecticide-impregnated mosquito net are justified in their use to control malaria in highly malaria-endemic areas in western Thailand.

Cost and performance of malaria sector: a case study at Malaria Sector 11, Tak Province, Thailand.

The objective of this study was to assess the cost and performance of each operational unit at the malaria sector level and to calculate the unit cost of each activity accordingly. Data were collected at Malaria Sector No.11 situated at the western border of Thailand with Myanmar during the fiscal year of 1995. The unit cost was calculated by dividing the total cost of each activity by its output using appropriate units of analysis. The result showed that 67% of the total cost of malaria sector was labor cost and 45% of the total cost was allocated to diagnosis and treatment activities. Unit cost in terms of cost/visit, cost/case found, cost/case of falciparum malaria treated, cost/case of vivax malaria treated, cost/house spray and cost/impregnated net were US$1.85, 8.21, 10.07, 8.46, 2.24 and 1.54 respectively. The results of this study will provide important information as to the best use of limited available resources to determine which activities should be stopped, continued, increased or decreased at the malaria sector level.

Cost-effectiveness analysis of lambdacyhalothrin-treated nets for malaria control: the patients' perspective.

The present study was undertaken to evaluate the cost-effectiveness of lambdacyhalothrin-treated nets in comparison with conventional DDT-spraying as a method of malaria control according to the patients' perspective among migrant populations in a high-risk area along the Thai-Myanmar border in Thailand. Ten hamlets comprising 243 houses with 948 inhabitants were given only treated nets. Twelve hamlets comprising 294 houses and 1,315 inhabitants represented the DDT-treated area and another six hamlets with 171 houses and 695 inhabitants served as controls. Information as to consumer costs was obtained by interviewing 3,214 patients seeking care at all levels of the health care system in the study area. Analysis showed that the impregnated-net program was more cost-effective than the DDT-spraying program or surveillance alone (US$ 0.59 vs US$ 0.74 vs US$ 0.79 per 1 case of prevented malaria). We conclude that in a high-risk area such as along the Thai-Myanmar border in western Thailand, integrating the use of impregnated nets with large-scale primary health care programs is likely to constitute the most cost-effective method for controlling malaria according to the patients' perspective.

The effect of pyrethroid impregnated mosquito nets on field malaria vector populations in experimental huts and in individual local houses.

Studies were carried out in Tak Province, northwest Thailand to determine repellency and killing effects of four commercially available pyrethroids etofenprox, deltamethrin, lambdacyhalothrin and permethrin treated mosquito nets on field malaria vector populations in experimental huts and local houses. The studies reveal that all four test pyrethroids have a highly repellency effect. Repellency ratio between lifted and torn nets also showed some different among the four pyrethroids. Mosquito net treated with 0.3 g/m2 permethrin was most toxic to mosquito followed by 0.02 g/m2 deltamathrin, etofenprox 0.3 g/m2 and 0.02 g/m2 lambdacyhalothrin. However, careful consideration for future use should also include problem of cross-resistance, persistence of chemicals and also type of mosquito net material.

Behaviors in self-prevention of malaria among mobile population in east Thailand.

The study investigated preventive behaviors among mobile villagers in Chanthaburi and Trat Provinces where the slide positive rates (SPR) of malaria in 1987 were 10.3 and 11.1%, respectively. The study was conducted in four villages namely Wang Thong, Khao Thong in Chanthaburi, and Manow and Khow in Trat by using a cross-sectional survey. Household and in-depth interviews with the movers were done together with field observations. The sizes of the villages were 52, 180, 184 and 209 households and the movement rates were 23.1, 12.2, 37.5 and 28.7%, respectively. The population involved in short term migration was 729 villagers living in 153 households or 23.7% of the total. Malaria prevalence rates in the four villages were 7.5%, 5.9%, 7.3% and 2.2%, respectively. The results indicate that the mobile population had a moderate 40% rating score of knowledge about malaria. Apparently, the rating score of preventive behaviors of the disease appeared to be as small as 20%. After six months of field investigations, 1,083 thick blood smears collected from the mobile population, there were 657 episodes (60.7%) of malaria that could be categorized with age specific prevalence of 60.3% in 19-29 years, 80.8% in 30-39 years, 54.8% in 40-49 years, 38.6% in 50-59 years and 35.7% in 60 years and over. Villagers aged between 30-39 years with frequent movement into the forest had the highest impact of malaria risk. Moderate levels of knowledge and attitude scores did not appear to enable the people to protect themselves against malaria.

Comparison between microscopic examination, ELISA and quantitative buffy coat analysis in the diagnosis of falciparum malaria in an endemic population.

Monoclonal antibody-based ELISA and QBC (quantitative buffy coat analysis) were tested in two endemic areas with low and high incidence of malaria in Kanchanaburi Province, West Thailand with annual parasite incidence in 1992 of 119 and 5 per 1,000 population, respectively. The numbers of individuals positive by thick blood film examination (TBF) for P. falciparum with or without P. vivax, and P. vivax only were 82 and 69, respectively. The detection limit of ELISA was 10 parasites/10(6) red blood cells (RBC) (0.001% parasitemia). Of 1,095 individuals involved in the study at the beginning of the study, ELISA showed sensitivity, specificity, positive predictive value and negative predictive value of 78.1%, 94.9%, 72% and 98.1%, respectively. Nine of 18 (50%) TBF-positive but ELISA-positive individuals had parasitemia of less than 10 parasites/10(6) RBC. High and low incidence areas did not affect the validity of our result. Regression analysis showed good correlation between log parasitemia and ELISA percent OD increase (Y = 0 + 64.9*logX, r = 0.65), and agreement between TBF and ELISA results was 95.9%. In a fortnightly follow-up, in 82 TBF-positive individuals, both ELISA and TBF positive rates correlatively declined with agreement of 96.3%. With samples taken on the first day of the study, the TBF and QBC results were also correlated with agreement of 95.8% for P. falciparum, 95.6% for P. vivax. During 8 week follow-up involving altogether 191 samples, agreement between TBF and QBC results were 87.4% for P. falciparum. QBC detected more cases with P. falciparum infections but detected smaller number of cases with P. vivax infections.

Economic analysis of malaria control for migrant workers in eastern Thailand.

A randomized, double-blind field trial was carried out to compare the economic impact of permethrin-treated nets with that of untreated nets as a method of malaria control. The study was conducted in 261 long-term migrant workers and 138 seasonal agricultural migrant workers in the eastern rural areas known to be highly endemic for multidrug-resistant Plasmodium falciparum infection. One hundred and twenty-six longterm migrants and 59 seasonal migrants used treated nets, while 135 and 79, respectively, used untreated nets. The impregnated-nets program was cost-saving as well as offering improved effectiveness. The net benefit of using a treated net was US$1.17 per worker from the Malaria Division's perspective and US$1.61 per worker from the worker viewpoint. The use of impregnated nets with large-scale primary health care programs likely will be the most cost-effective and cost-beneficial method for controlling malaria in eastern Thailand.

The effectiveness of permethrin-impregnated bed nets against malaria for migrant workers in eastern Thailand.

A randomized, double-blind, field trial was carried out to compare the effectiveness of permethrin-treated bed nets with that of untreated nets as a method of malaria control for migrant workers in eastern Thailand. The study was conducted using 261 subjects in eastern rural areas that are known to be highly endemic for multidrug-resistant Plasmodium falciparum infection. One hundred twenty-six subjects used treated nets, while 135 used untreated nets. During the 35 weeks of observation, 23 subjects using treated nets and 33 workers using untreated nets developed 28 and 51 episodes of malaria, respectively (P = 0.029). The reduction in risk per subject due to treated nets was 0.06. The residual effects of permethrin were tested using a World Health Organization standard bioassay. Anti-mosquito activity was found to be present in the nets for more than 16 months. We conclude that because of the failure of the development of safe, effective, long-lasting prophylactic agents, integrating the use of impregnated nets with large-scale primary health care programs may be a partially effective method for controlling malaria in eastern Thailand.

Circumsporozoite protein heterogeneity in the human malaria parasite Plasmodium vivax.

Phenotypic heterogeneity in the repetitive portion of a human malaria circumsporozoite (CS) protein, a major target of candidate vaccines, has been found. Over 14% of clinical cases of uncomplicated Plasmodium vivax malaria at two sites in western Thailand produced sporozoites immunologically distinct from previously characterized examples of the species. Monoclonal antibodies to the CS protein of other P. vivax isolates and to other species of human and simian malarias did not bind to these nonreactive sporozoites, nor did antibodies from monkeys immunized with a candidate vaccine made from the repeat portion of a New World CS protein. The section of the CS protein gene between the conserved regions I and II of a nonreactive isolate contained a nonapeptide repeat, Ala-Asn-Gly-Ala-Gly-Asn-Gln-Pro-Gly, identical at only three amino acid positions with published nonapeptide sequences. This heterogeneity implies that a P. vivax vaccine based on the CS protein repeat of one isolate will not be universally protective.

Bionomics of Anopheles maculatus complex and their role in malaria transmission in Thailand.

The bionomics of Anopheles maculatus complex and its role in malaria transmission were conducted in Pakchong and Sadao districts, Nakhon Ratchasima and Songkhla provinces, respectively, from January 1984 to July 1985. In Pakchong, An. maculatus species A was the most dominant species, followed by species B form F and species C which was rare. The densities of species A and species B form F were high between July and November, with their peaks in October. Biting activities of both species occurred through out the night, with a major peak during the first quarter of the night on all seasons. In Sadao, only An. maculatus species B form E was detected with peak densities between February and June. Biting activities of this species varied according to seasons. The prevalence of mosquitoes was influenced by monthly rainfall, relative humidity and air-temperature. All species of female An. maculatus complex studied prefered to feed on animal rather than on human, and tended to bit human more outdoors than indoors, and thus exhibiting a zoophilic and exophagic behaviour. Life expectancies of An. maculatus species A ranged from 1.6 to 6.6 days, species B form F from 1.1 to 8.1 days, and species B form E from 0.7 to 21.2 days. The natural malaria infection rate was very low. Out of 4,430 guts dissected, only 0.23% were found infected with oocysts. There were no sporozoites detected in the 4,472 dissected salivary glands.

Bionomics of Anopheles minimus and its role in malaria transmission in Thailand.

The bionomics of Anopheles minimus, one of the main malaria vectors in Thailand, were conducted in Pakchong district, Nakhon Ratchasima province, from January 1984 to June 1985. The prevalence of An. minimus was influenced by monthly rainfall, relative humidity, temperature and wind velocity, with a major peak of density from September to November. An. minimus preferred to feed on animal rather than on human, tended to bite human more outdoors than indoors, and thus exhibiting zoophilic and exophilic behaviour. The biting activity of the mosquitoes on animal exhibited high densities throughout the night in all seasons, whereas on human they tended to be an early evening biter in the dry cool season, and early morning biter in the wet season, and thus increasing the chance of man-vector contact. The life expectancy of An. minimus varied from month to month, ranging from 2.7 to 11.5 days, with the longest longevity during the dry cool season. The natural malaria infection rate of this species was very low. Out of 1,518 dissected guts, only 0.4% were found infected with oocysts. There were no sporozoites detected in the 1,560 dissected salivary glands.

Cost-effectiveness research in malaria control and the need for health behaviour and socio-economic research in malaria control in Thailand.

The complexity of the malaria situation in Thailand requires behavioural and socio-economic research in wide variety of areas including; migration, illness behaviour, motivation of staff and communities and the relationship of institutional and community expenditure to reduction in morbidity. The research ideally should be constructed in such a way as to maximize the availability of methods for incorporation into routine monitoring, evaluation, and policy making activities of the Anti-Malaria Programme.

Effects of cyromazin and methoprene on the developmental stages of Anopheles dirus, Aedes aegypti and Culex quinquefasciatus (Diptera : Culicidae).

The effects of two chemical compounds, cyromazin and methoprene, on the developmental stages of Anopheles dirus, Aedes aegypti and Culex quinquefasciatus were investigated under laboratory conditions, with the mean temperature of 24 degrees +/- 1 degree C and the relative humidity at 65-75%. Both compounds were tested against the second, third and fourth instar larvae. The concentrations of cyromazin used for An. dirus and Cx. quinquefasciatus ranged from 0.0008 to 0.5 mg/l; and for Ae. aegypti from 0.004 to 2.5 mg/l. The concentrations of methoprene used for An. dirus, Ae. aegypti and Cx. quinquefasciatus ranged from 0.00016 to 0.1 mg/l. The mortality rates were found to be relatively high in larval and pupal stages when treated with cyromazin and methoprene. The primary toxic effects of cyromazin were on the second stage larvae. The LC50 values for cyromazin on the second, third and fourth stage larvae were, respectively, 0.0027, 0.0042 and 0.0114 mg/l for An. dirus, and 0.1662, 0.2307 and 0.3005 mg/l for Ae. aegypti. Cx. quinquefasciatus was the most sensitive species to cyromazin with LC50 values for second, third and fourth stage larvae of 0.0015, 0.0068 and 0.0130 mg/l, respectively. The primary toxic effects of methoprene were in the fourth stage larvae. The LC50 values for methoprene on the second, third and fourth stage larvae were, respectively, 0.0110, 0.0041 and 0.0022 mg/l for An. dirus, and 0.0077, 0.0034 and 0.0025 mg/l for Ae. aegypti. Cx. quinquefasciatus was the most sensitive species to methoprene, with LC50 values for second, third and fourth stage larvae of 0.0013, 0.0008 and 0.0006 mg/l, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)