Felix P. Amerasinghe

Impact of urban agriculture on malaria vectors in Accra, Ghana

To investigate the impact of urban agriculture on malaria transmission risk in urban Accra larval and adult stage mosquito surveys, were performed. Local transmission was implicated as Anopheles spp. were found breeding and infected Anophele s mosquitoes were found resting in houses in the study sites. The predominant Anopheles species was Anopheles gambiae s.s.. The relative proportion of molecular forms within a subset of specimens was 86% S-form and 14% M-form. Anopheles spp. and Culex quinquefasciatus outdoor biting rates were respectively three and four times higher in areas around agricultural sites (UA) than in areas far from agriculture (U). The annual Entomological Inoculation Rate (EIR), the number of infectious bites received per individual per year, was 19.2 and 6.6 in UA and U sites, respectively. Breeding sites were highly transitory in nature, which poses a challenge for larval control in this setting. The data also suggest that the epidemiological importance of urban agricultural areas may be the provision of resting sites for adults rather than an increased number of larval habitats. Host-seeking activity peaked between 2–3 am, indicating that insecticide-treated bednets should be an effective control method.

STRONG ASSOCIATION BETWEEN HOUSE CHARACTERISTICS AND MALARIA VECTORS IN SRI LANKA

The objective of this study was to determine whether house characteristics could be used to further refine the residual insecticide-spraying program in Sri Lanka. Indoor-resting mosquito densities were estimated in 473 houses based on fortnightly collections over a two-and-a-half-year period. The type of house construction and the exact location of all houses were determined. In a multivariate analysis, distance of less than 750 meters between a house and the main vector-breeding site was strongly associated with the presence of Anopheles culicifacies in the house (odds ratio [OR] 4.8, 95% confidence interval [CI] 3.4-6.8) and to a lesser extent with the presence of An. subpictus (OR 1.4, 95% CI 1.1-1.7). Poor housing construction also was an independent risk factor (OR for An. culicifacies 1.3, 95% CI 1.0-1.9; OR for An. subpictus 1.3, 95% CI 1.0-1.6). It is recommended that a malaria control strategy focus on residential areas within 750 meters of streams and rivers, with special attention given to areas with the poorest type of house construction.

Anthropophagy and aggregation behaviour of the sandfly Phlebotomus argentipes in Sri Lanka.

ABSTRACT. The visceral leishmaniasis (VL) vector Phlebotomus argentipes Annandale & Brunetti is widely distributed throughout the Indian sub‐continent and S.E. Asia. The absence of VL in areas such as Sri Lanka has been attributed to the zoophilic nature of P.argentipes, since they were not recorded biting man.

Malaria and Irrigated Crops, Accra, Ghana

We investigated the prevalence of malaria and associated risk factors in children living in urban Ghana. Malaria prevalence was associated with low hemoglobin concentration, low socioeconomic status, and higher age. Our findings indicate that African urban poor are seriously affected by malaria and that irrigated agriculture may increase this risk.

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).

Japanese encephalitis in Sri Lanka: comparison of vector and virus ecology in different agro-climatic areas

The ecology of Japanese encephalitis (JE) in different agro-climatological areas of Sri Lanka was studied in relation to the abundance of mosquito vectors, infection in domestic livestock, and human infection and disease. There was an inverse correlation between altitude and the abundance of potential JE vectors, as well as JE seroprevalence in domestic livestock and in man. Little or no JE infection was documented above 1200 m elevation. JE seroprevalences in cattle and goats were better predictors of human infection risk than was porcine seroprevalence. In areas with asynchronous porcine infection occurring over many months, high overall JE seroprevalence in pigs was found with little evidence of human infection. Porcine JE infection occurring in synchronous bursts associated with monsoonalrains was correlated with significant bovine, ovine and human seroprevalence in 2 low elevation study areas, Anuradhapura (dry zone) and Ragama (wet zone), with epidemic human JE in the former area and endemic disease in the latter.

Urban malaria and anaemia in children: a cross-sectional survey in two cities of Ghana.

Objective  To describe the epidemiology of urban malaria, an emerging problem in sub‐Saharan Africa.

Maps of the Sri Lanka malaria situation preceding the tsunami and key aspects to be considered in the emergency phase and beyond

BackgroundFollowing the tsunami, a detailed overview of the area specific transmission levels is essential in assessing the risk of malaria in Sri Lanka. Recent information on vector insecticide resistance, parasite drug resistance, and insights into the national policy for malaria diagnosis and treatment are important in assisting national and international agencies in their control efforts.MethodsMonthly records over the period January 1995 – October 2004 of confirmed malaria cases were used to perform an analysis of malaria distribution at district spatial resolution. Also, a focused review of published reports and routinely collected information was performed.ResultsThe incidence of malaria was only 1 case per thousand population in the 10 months leading up to the disaster, in the districts with the highest transmission.ConclusionAlthough relocated people may be more exposed to mosquito bites, and their capacity to handle diseases affected, the environmental changes caused by the tsunami are unlikely to enhance breeding of the principal vector, and, given the present low parasite reservoir, the likelihood of a malaria outbreak is low. However, close monitoring of the situation is necessary, especially as December – February is normally the peak transmission season. Despite some losses, the Sri Lanka public health system is capable of dealing with the possible threat of a malaria outbreak after the tsunami. The influx of foreign medical assistance, drugs, and insecticides may interfere with malaria surveillance, and the long term malaria control strategy of Sri Lanka, if not in accordance with government policy.

Sri Lanka malaria maps

BackgroundDespite a relatively good national case reporting system in Sri Lanka, detailed maps of malaria distribution have not been publicly available.MethodsIn this study, monthly records over the period 1995 – 2000 of microscopically confirmed malaria parasite positive blood film readings, at sub-district spatial resolution, were used to produce maps of malaria distribution across the island. Also, annual malaria trends at district resolution were displayed for the period 1995 – 2002.ResultsThe maps show that Plasmodium vivax malaria incidence has a marked variation in distribution over the island. The incidence of Plasmodium falciparum malaria follows a similar spatial pattern but is generally much lower than that of P. vivax. In the north, malaria shows one seasonal peak in the beginning of the year, whereas towards the south a second peak around June is more pronounced.ConclusionThis paper provides the first publicly available maps of both P. vivax and P. falciparum malaria incidence distribution on the island of Sri Lanka at sub-district resolution, which may be useful to health professionals, travellers and travel medicine professionals in their assessment of malaria risk in Sri Lanka. As incidence of malaria changes over time, regular updates of these maps are necessary.

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.