Physico-chemical characteristics of Anopheles culicifacies and Anopheles varuna breeding water in a dry zone stream in Sri Lanka.

BACKGROUND & OBJECTIVES: Selected physico-chemical characteristics of flowing and pooled water in a stream that generated two malaria vectors, Anopheles culicifacies s.l. Giles and Anopheles varuna Iyengar, were investigated during August-September 1997 and July 1998 at the Upper Yan Oya watershed in north-central Sri Lanka. METHODS: The physico-chemical parameters measured were: temperature, dissolved oxygen, pH, conductivity, total dissolved solids, alkalinity, ammonia nitrogen, nitrate nitrogen, calcium, magnesium, carbondioxide, ferrous iron, phosphate, colour and turbidity. In total, 75.5% of 151 samples analysed were mosquito-positive. Logistic regression was used for statistical analysis. RESULTS: Among physico-chemical parameters, An. culicifacies (the major malaria vector in the country) was positively related only to temperature, and An. varuna (a secondary malaria vector) to calcium. Among habitat characteristics, An. culicifacies was associated with light and vegetation, and negatively associated with the presence of potential predators. An. varuna was positively associated with other aquatic fauna. INTERPRETATION & CONCLUSION: Surprisingly this detailed study did not find an association between An. culicifacies and dissolved oxygen as previously found in the few studies that have looked at physico-chemical characteristics of malaria vector breeding habitats in south Asia. This study, along with existing information from other studies indicate that most of the physico-chemical parameters measured under natural conditions within the same habitat type is insufficient to explain the distribution of vectors within such habitats. However, it seems likely that both An. culicifacies and An. varuna follow a strategy whereby ovipositing females scatter their eggs over most of or all of a highly temporary and only transiently available stream bed pool habitat, in order to optimise breeding success.

Food of larval Anopheles culicifacies and Anopheles varuna in a stream habitat in Sri Lanka.

No previous studies have been conducted on the natural food of larval Anopheles culicifacies s.l. (the major malaria vector) and An. varuna (a secondary vector) in Sri Lanka. The present study analyzed the contents of guts dissected from larvae collected from pools in a natural stream-cum-irrigation conveyance channel in the Upper Yan Oya watershed in the North Central Province of the country during August-September 1997 and July 1998. Determinations of physicochemical and biological parameters of the pools and their water were done at the same time. A fluorochromatic stain, 4',6-diamidino-2-phenylindole, was used to stain larval gut contents. Quantitative estimates of different categories of food types were made by analyzing the gut contents of 95 An. culicifacies (26 second instars and 69 fourth instars) and 52 An. varuna (21 second instars and 31 fourth instars). Detritus was the most frequent food type, comprising >74% of the gut contents in both species. Other food types included bacteria (cocci and rods), filamentous algae, diatoms, and desmids. Overall, bacteria constituted a significantly higher proportion of the gut contents in An. culicifacies than in An varuna. Significantly more detritus, bacteria, and total particulate matter occurred in 4th instars of An. culicifacies than in An. varuna, indicating a greater food intake in the former species. Second instars of An. culicifacies and An. varuna did not differ significantly in any parameter. A significant increase in food intake between 2nd and 4th instars was seen for An. culicifacies, but not An. varuna. Food indices were lower in An. varuna than in An. culicifacies when the 2 species co-occurred, indicating competition for food, and the implications of this to adult body size, survival, and fecundity are discussed.

Adult anopheline ecology and malaria transmission in irrigated areas of South Punjab, Pakistan.

Surface irrigation in the Punjab province of Pakistan has been carried out on a large scale since the development of the Indus Basin Irrigation System in the late 19th century. The objective of our study was to understand how the population dynamics of adult anopheline mosquitoes (Diptera: Culicidae) could be related to malaria transmission in rural areas with intensive irrigation and a history of malaria epidemics. In this paper we present our observations from three villages located along an irrigation canal in South Punjab. The study was carried out from 1 April 1999 to 31 March 2000. Mosquitoes were collected from bedrooms using the pyrethroid spraycatch method and from vegetation and animal sheds using backpack aspirators. Overall, Anopheles subpictus Grassi sensu lato predominated (55.6%), followed by An. stephensi Liston s.l. (41.4%), An. culicifacies Giles s.l. (2.0%), An. pulcherrimus Theobald (1.0%) and An. peditaeniatus Leicester (0.1%). Most mosquitoes (98.8%) were collected from indoor resting-sites whereas collections from potential resting-sites outdoors accounted for only 1.2% of total anopheline densities, confirming the endophilic behaviour of anophelines in Pakistan. Anopheles stephensi, An. culicifacies and An. subpictus populations peaked in August, September and October, respectively. High temperatures and low rainfall negatively affected seasonal abundance in our area. There were interesting differences in anopheline fauna between villages, with An. culicifacies occurring almost exclusively in the village at the head of the irrigation canal, where waterlogged and irrigated fields prevailed. Monthly house-to-house fever surveys showed that malaria transmission remained low with an overall slide positivity rate of 2.4% and all cases were due to infection with Plasmodium vivax. The most plausible explanation for low transmission in our study area seems to be the low density of Pakistan's primary malaria vector, An. culicifacies. The role of other species such as An. stephensi is not clear. Our observations indicate that, in South Punjab, irrigation-related sites support the breeding of anopheline mosquitoes, including the vectors of malaria. As our study was carried out during a year with exceptionally hot and dry climatic conditions, densities and longevity of mosquitoes would probably be higher in other years and could result in more significant malaria transmission than we observed. To assess the overall importance of irrigation-related sites in the epidemiology of malaria in the Punjab, more studies are needed to compare irrigated and non-irrigated areas.

Human otoacariasis: a retrospective study from an area of Sri Lanka.

Intra-aural ticks were present in 870 (15.2%) of 5714 patients who reported with ear-related complaints to the ear, nose and throat ward at Ratnapura Hospital, Sabaragamuwa Province, Sri Lanka, from January 2000 to December 2001. A retrospective study of 383 of these otoacariasis cases showed that the majority (70.8%) of surgically-removed ticks were nymphal Amblyomma integrum, together with nymphal and adult Rhipicephalus haemaphysaloides, R. sanguineus, Hyalomma brevipunctata, H. marginatum, and unidentified (damaged) ticks (collectively, 29.2%). Tick infestations peaked during the period November-February. More female than male patients reported with otoacariasis, and more children (aged 0-10 years) and adults (aged >/=21 years) than adolescents. There was no evidence of age-dependent differences in infestation among male and female patients. The tick-infested cases were widespread, spanning 75 km on a north-south axis and 55 km on an east-west axis within Sabaragamuwa Province. The present report represents the largest episode of human otoacariasis recorded in the literature, and may be indicative of a wider, but little-reported, human tick problem in Sri Lanka.

Breeding of Anopheles mosquitoes in irrigated areas of South Punjab, Pakistan.

As part of investigations on potential linkages between irrigation and malaria transmission, all surface water bodies in and around three villages along an irrigation distributary in South Punjab, Pakistan, were surveyed for anopheline mosquito larvae (Diptera: Culicidae) from April 1999 to March 2000. Samples were characterized according to exposure to sunlight, substratum, presence of vegetation, fauna, inorganic matter and physical water condition (clear/turbid/foul). Also water temperature, dissolved oxygen (DO), electroconductivity (EC) and pH of sites were recorded. A total of 37982 Anopheles larvae of six morphological types were collected from 2992 samples taken from irrigation/agricultural and village/domestic aquatic habitats. Anopheles subpictus Grassi sensu lato was by far the most abundant (74.3%), followed by An. culicifacies Giles s.l. (4.1%), An. stephensi Liston s.l. (2.6%), An. pulcherrimus Theobald (1.8%), An. peditaeniatus Leicester (0.3%) and An. nigerrimus Giles (0.1%). The four most abundant species were significantly associated with waterlogged fields and communal village drinking-water tanks. Habitat characteristics most correlated with occurrence of anophelines were the physical water condition and the absence/presence of fauna, particularly predators. Occurrence and abundance of Anopheles immatures were not significantly correlated with water temperature, DO, EC or pH. Malaria vectors of the Anopheles culicifacies complex occurred at relatively low densities, mainly in irrigated and waterlogged fields. In South Punjab, where rainfall is very low, it should be possible to reduce anopheline breeding through water management, as larvae develop mainly in water bodies that are directly or indirectly related to the extensive canal-irrigation system.

A village treatment center for malaria: community response in Sri Lanka.

Early diagnosis and treatment of malaria cases is one of the basic elements of the current global malaria control strategy. In order to provide this service to people in rural areas there is a need for new cost-effective approaches. To ensure that such new approaches are acceptable to the target communities, it is important to know the rationale for people's malaria treatment-seeking behavior. The present study provides insights into the reasons for people's preferences for different types of healthcare facilities and describes variation of these preferences within a rural community in Sri Lanka. The study reports on the experiences with the establishment of a village health facility and its effect on the treatment-seeking behavior of the population. After the introduction of the village treatment center it quickly took over the role of main provider for diagnosis and treatment of malaria from the government facilities. The treatment center did not improve the response time in seeking treatment for young children, but the delay for adults was reduced by 1-2 days. Mothers with small children often preferred the government facilities since they wanted a more qualified opinion than available from the locally recruited staff of the village treatment center. The treatment center significantly reduced the stress and discomfort experienced by the elderly and handicapped segment of the community. The study indicated that the effective catchment area of a village treatment center will be influenced by the degree of initial support from key individuals in the communities, the selection procedure and training of assistants, and the history of the relationships between different villages to be served by the center. The government health services and communities across the dry zone of Sri Lanka could benefit substantially from the establishment of more village treatment centers. To ensure the long-term sustainability of these type of facilities it is necessary to assess the feasibility of charging a user fee and establishing multi-purpose clinics. Government policies and administrative procedures will need to be adjusted to make the successful operation of village treatment centers possible.

Multiple host feeding in field populations of Anopheles culicifacies and An. subpictus in Sri Lanka.

A histological technique was used to detect the multiple blood-feeding of female mosquitoes, within the same gonotrophic cycle, in field populations of the malaria vectors Anopheles culicifacies and An. subpictus (Diptera: Culicidae) at a village in the low country of Sri Lanka, during 1994-96. Among 3306 An. culicifacies and 871 An. subpictus engorged females examined, respectively, 34.4% and 30.4% were multiple-fed. In these two species, double meals accounted for 92.7% and 89.5%, and triple meals for 7.3% and 10.5% of multiple meals, respectively. More females of An. culicifacies (53.7%) than An. subpictus (44.5%) multiple-fed on different nights. Multiple feeding rates in the two species were independent of sample size and field abundance. In An. culicifacies, but not An. subpictus, these rates were proportional to ambient temperature but not to humidity. Bloodmeal ELISA showed that 8.3% of 242 An. culicifacies were human-fed and 80% of these (i.e. 6.6%) were concurrently bovid-fed. Combining the histological and ELISA data, it was estimated that multiple feeding involving a human host had occurred in 7.2% of the blood-feeding An. culicifacies population at this study site. Only 1.2% of 406 An. subpictus were human-fed and all of these were concurrently bovid-fed. Multiple bloodfeeding within the same gonotrophic cycle was attributed to a local 'frequent feeding strategy' in these primarily zoophagic and endophilic malaria vectors. Unfortunately this strategy enhances their human-biting rate and hence their vectorial capacity.

Malaria vectors in a traditional dry zone village in Sri Lanka.

Malaria transmission by anopheline mosquitoes was studied in a traditional tank-irrigation-based rice-producing village in the malaria-endemic low country dry zone of northcentral Sri Lanka during the period August 1994-February 1997. Adult mosquitoes were collected from human and bovid bait catches, bovid-baited trap huts, indoor catches, and pit traps. Mosquito head-thoraces were tested for the presence of Plasmodium falciparum and P. vivax, and blood-engorged abdomens for the presence of human blood by ELISAs. House surveys were done at two-day intervals to record cases of blood film-confirmed malaria among the villagers. A total of 7,823 female anophelines representing 14 species were collected. Trends in anopheline abundance were significantly correlated with rainfall of the preceding month in An. annularis, An. barbirostris, An. subpictus, An. vagus, and An. varuna, but were not significant in An. culicifacies and An. peditaeniatus. Malaria parasite infections were seen in seven mosquito species, with 75% of the positive mosquitoes containing P. falciparum and 25% P. vivax. Polymorph PV247 was recorded from a vector (i.e., An. varuna) for the first time in Sri Lanka. Computations of mean number of infective vector (MIV) rates using abundance, circumsporozoite (CS) protein rate, and human blood index (HBI) showed the highest rate in An. culicifacies. A malaria outbreak occurred from October 1994 to January 1995 in which 45.5% of village residents experienced at least a single disease episode. Thereafter, malaria incidence remained low. Anopheles culicifacies abundance lagged by one month correlated positively with monthly malaria incidence during the outbreak period, and although this species ranked fifth in terms of abundance, infection was associated with a high MIV rate due to a high CS protein rate and HBI. Abundance trends in other species did not correlate significantly with malaria. It was concluded that An. culicifacies was epidemiologically the most important vector in the study area.

Cost of malaria control in Sri Lanka.

The study provides estimates of the cost of various malaria control measures in an area of North-Central Province of Sri Lanka where the disease is endemic. We assumed that each measure was equally effective. In these terms, impregnating privately purchased bednets with insecticide was estimated to cost Rs 48 (US(40.87) per individual protected per year, less than half the cost of spraying houses with residual insecticides. Larviciding of vector breeding sites and especially the elimination of breeding habitats by flushing streams through seasonal release of water from upstream reservoirs was estimated to be cheaper than other preventive measures (Rs 27 (US$ 0.49) and Rs 13 (US$ 0.24) per individual protected, respectively). Inclusion of both operational and capital costs of treatment indicates that the most cost-effective intervention for the government was a centrally located hospital with a relatively large catchment area (Rs 71 (US$ 1.29) per malaria case treated). Mobile clinics (Rs 153 (US$ 2.78) per malaria case treated) and a village treatment centre (Rs 112 (US$ 2.04)) per malaria case treated) were more expensive options for the government, but were considerably cheaper for households than the traditional hospital facilities. This information can guide health planners and government decision-makers in choosing the most appropriate combination of curative and preventive measures to control malaria. However, the option that is cheapest for the government may not be so for the householders, and further studies are needed to estimate the effectiveness of the various preventive measures.

PIP: A large proportion of Sri Lanka's budget is spent on malaria control. Estimates are provided of the cost of various malaria control interventions in North-Central Province, Sri Lanka, where the disease is endemic and where ongoing research activities facilitated the cost-effectiveness assessment. Each measure considered was assumed to be equally effective. As such, impregnating privately purchased bednets with insecticide was estimated to cost Rs 48 (US$0.87) per person protected per year, less than half the cost of spraying houses with residual insecticides. The larviciding of vector breeding sites and eliminating breeding habitats by flushing streams through the seasonal release of water from upstream reservoirs was estimated to be cheaper than other preventive measures, at Rs 27 and Rs 13 per person protected, respectively. Including both the operational and capital costs of treatment indicates that the most cost-effective intervention for the government was a centrally located hospital with a relatively large catchment area, at Rs 71 per malaria case treated. Mobile clinics and a village treatment center approach cost Rs 153 and Rs 112, respectively, per malaria case treated. These latter 2 strategies were the more expensive options for the government, but were less expensive for households compared to the cost of treatment at traditional hospital facilities.

Serologic evidence for an epizootic dengue virus infecting toque macaques (Macaca sinica) at Polonnaruwa, Sri Lanka.

Dengue is one of the most rapidly emerging diseases in the tropics. Humans are the principal reservoir of dengue viruses. It is unclear if nonhuman primates also serve as a reservoir of human dengue viruses under certain conditions. In this study, a cross-sectional serologic survey was carried out to characterize the pattern of transmission of a recently identified dengue virus among toque macaques in Sri Lanka. The results indicated that an epizootic dengue virus was active among the macaques. A single epizootic had taken place between October 1986 and February 1987 during which 94% of the macaques within the 3 km2 study site were exposed to the virus. The epizootic was highly focal in nature because macaques living 5 km from the study population were not exposed to the virus. The transmission of dengue viruses among macaques in the wild may have important public health implications.

Risk factors for malaria: a microepidemiological study in a village in Sri Lanka.

Environmental and socioeconomic risk factors for malaria were studied in a village in Sri Lanka. Over a period of one year, all 49 households in the village were visited every alternate day to obtain information on malaria episodes. Information on risk factors was obtained through questionnaires and direct observations. Age below 17 years (relative risk [RR] = 1.66, 95% confidence interval [95% CI] 1.18-2.35), use of bed nets (RR = 0.16, 95% CI 0.05-0.45) and traditional fumigants (RR = 0.58, 95% CI 0.37-0.93) were independent predictors of malaria. People using anti-mosquito pyrethrum coils had a higher risk for malaria than people living in houses where they were not used (RR = 1.46, 95% CI 1.03-2.07). The build-up of Anopheles culicifacies populations before the start of the transmission season had taken place in a stream near the village. Living close to the stream was a risk factor for malaria early in the transmission season, although this did not reach statistical significance (comparing < 250 m with > 500 m, RR = 2.13, 95% CI 0.96-4.71).

Anopheles culicifacies breeding in Sri Lanka and options for control through water management.

This paper assesses the options for control of malaria vectors through different water management practices in a natural stream in Sri Lanka. The association between water level in the stream and breeding of the immature stages of the primary vector Anopheles culicifacies was investigated and the feasibility of using existing irrigation infrastructure to reduce the breeding potential discussed. The most feasible option would be to implement a management routine where water is released periodically from an upstream reservoir to reduce the number of breeding sites downstream. This study indicates that by regulating the water level above 20 cm in the stream throughout the dry season the breeding of A. culicifacies could be significantly reduced. The intervention would have only limited impact on the water lost for agriculture and the management input would be minimal. However, for the intervention to work a high degree of support from the local community is essential and consultation between government departments needed.

Characteristics of malaria vector breeding habitats in Sri Lanka: relevance for environmental management.

In and around a village in the Anuradhapura District of Sri Lanka anopheline larvae were sampled from July 1994 to April 1996 in all surface water bodies. Samples positive for Anopheles culicifacies, the established vector of malaria in Sri Lanka, and for An. barbirostris, An. vagus, and An. varuna, potential secondary vectors, were characterized by site, exposure to sunlight, substratum, turbidity of the water, presence of vegetation, and presence of fauna. Availability of pools of stagnant water in the stream near the village and along the edge of the village tank was highly predictive for presence of An. culicifacies larvae, independent from the other characteristics that were included in the study. The biological and physical characteristics could not very well explain the preference for certain habitats, but it was of interest that An. culicifacies, generally considered to bread in sun exposed clear water pools, was able to exploit habitats that were shaded and contained turbid water. Environmental management interventions to control An. culicifacies breeding have to take into account that the secondary vectors of malaria exploit other habitats and would not be affected by the interventions.

Measuring the economic cost of malaria to households in Sri Lanka.

The economic cost at the household level of labor days lost due to malaria and other illnesses was estimated in a rural community in Sri Lanka. Over a one-year period, 223 episodes of malaria were recorded from the 298 inhabitants of the village. Based on daily activity records, the economically active age group was defined as 14-60 years. In this age group, 1.8% of working days were lost due to malaria and 5.2% due to all other illnesses. The value of a labor day lost was based on the actual rural wage rate for children, women, and men, with weeks during periods of high labor demand weighting more than weeks during lean agricultural periods. In this way the annual economic loss per household amounted to US $15.56 for malaria and US $47.46 for all other illnesses. This corresponded to a loss of 6% and 18% of annual household net income, respectively. Although the overall economic impact was limited, malaria cases were concentrated in an important agricultural season. During this season, 5.6% of working days were lost due to malaria. In addition, children, who were not part of the economically active population, lost 10% of school days due to malaria during the high transmission season. In estimating the socioeconomic impact of malaria and in measuring cost-benefits of malaria control interventions, these costs have to be considered together with direct expenditures incurred by households such as on treatment and travel and with costs for the service providers.

Anopheline (Diptera:Culicidae) breeding in a traditional tank-based village ecosystem in north central Sri Lanka.

A 13-mo survey of immature anopheline mosquitoes breeding in surface water habitats was done at Mahameegaswewa village within the Huruluwewa watershed in north central Sri Lanka as part of a multidisciplinary study on malaria epidemiology. The watershed is representative of the ancient small tank-based irrigation network that still forms an important component of the rice production system in the low elevation dry zone. In total, 3,818 immatures representing 12 species were obtained from 2,940 samples taken from 5 larval habitats within the village ecosystem. Anopheles varuna Iyengar and An. culicifacies Giles were the most abundant species collected. Peak abundance in both species occurred in August-October. Anopheles barbirostris Van der Wulp and An. peditaeniatus Leicester also were abundant, but neither these nor the other anophelines attained comparable abundance to An. varuna and An. culicifacies. A clear progression in breeding habitat use from stream bed to tank bed and drainage area pools was seen in An. culicifacies during the premonsoon period. Environmental management measures to reduce or modify these habitats could potentially decrease malaria. transmission.

Household responses to malaria and their costs: a study from rural Sri Lanka.

A study of the cost of malaria at the household level, community perceptions, preventive measures and illness behaviour linked to the disease was undertaken in 5 villages in the dry zone of Sri Lanka. The surveyed community had a high knowledge of malaria, although side effects of antimalarial drugs were often confused with symptoms of the disease. The community sought prompt diagnosis and treatment at 'western-type' facilities, with 84% making use of government facilities as their first choice and 16% preferring private facilities. The preventive measures used were burning coils (54% of families) and special leaves (69% of families), and 93% of the families had their houses sprayed with insecticides. Average direct expenditure on a single malaria episode was $3 US, with some families spending more than 10% of the annual household net income per episode. The highest expenditure was on special diets for the sick person, to neutralize the perceived heating effect of the disease and its treatment.

PIP: Knowledge of community perceptions of malaria, treatment-seeking behaviors, and the household costs of illness is essential to the planning of sustainable malaria control interventions. These factors were investigated in household surveys conducted in 5 villages in Sri Lanka's dry zone in February 1995. 95% of the 216 families interviewed regarded malaria as their main health problem, followed by diarrhea and eye diseases. Malaria was ranked as the third most important community concern, following lack of water for cultivation and poverty. Overall knowledge of malaria's causes, symptoms, and treatment was high, although the side effects of antimalarial drugs were often confused with symptoms of the disease. Reported for the 3-month period preceding the survey were 178 episodes of malaria involving 160 families. Home treatment with paracetamol was the first step taken in 85% of cases; however, all families sought prompt treatment from Western-type facilities, especially government hospitals (48%) and mobile clinics (30%). No families consulted indigenous or ayurvedic physicians, despite their availability in the area. This utilization of prompt, effective treatment is presumed to reflect high knowledge about malaria, the perceived seriousness of the disease, and good transport facilities in the area. The total direct expenditure on a single episode of malaria averaged US $3; the median net annual income was $258. Special foods for malaria patients aimed at neutralizing the perceived heating effect of malaria and antimalarial drugs (e.g., sodas, oranges) were the most costly item. Adults lost an average of 7.8 days of work per episode and those accompanying them to health facilities lost 2.9 days. Preventive measures used by families included bed nets (23%), mosquito coils (54%), and insecticides (93%).

Predicting Ixodes scapularis abundance on white-tailed deer using geographic information systems.

We collected 1,410 Ixodes scapularis from 139 white-tailed deer in Kent County, Maryland during the 1990 hunting season. A geographic information system was used to extract 41 environmental variables in the areas surrounding the collection sites of the deer. Stepwise linear regression was used to evaluate the association between the abundance of ticks on deer and the environmental data. A significant statistical association was observed between the abundance of I. scapularis and seven environmental variables (R = 0.69). Tick abundance was negatively correlated with urban land use patterns, wetlands, the amount of privately owned land, soils that tended to be saturated with water, and one drainage system. Tick abundance was positively correlated with well-drained, sandy soils having low water tables. These results indicate that geographically referenced environmental data may be useful in anticipating the risk of exposure to vectors over large areas.