Active case detection for malaria elimination: a survey among Asia Pacific countries.

BACKGROUND: Moving from malaria control to elimination requires national malaria control programmes to implement strategies to detect both symptomatic and asymptomatic cases in the community. In order to do this, malaria elimination programmes follow up malaria cases reported by health facilities to carry out case investigations that will determine the origin of the infection, whether it has been imported or is due to local malaria transmission. If necessary, the malaria programme will also carry out active surveillance to find additional malaria cases in the locality to prevent further transmission. To understand current practices and share information on malaria elimination strategies, a survey specifically addressing country policies on case investigation and reactive case detection was carried out among fourteen countries of the Asia Pacific Malaria Elimination Network (APMEN). METHODS: A questionnaire was distributed to the malaria control programme managers amongst 14 countries in the Asia Pacific who have national or sub-national malaria elimination goals. RESULTS: Results indicate that there are a wide variety of case investigation and active case detection activities employed by the 13 countries that responded to the survey. All respondents report conducting case investigation as part of surveillance activities. More than half of these countries conduct investigations for each case. Over half aim to accomplish the investigation within one to two days of a case report. Programmes collect a broad array of demographic data during investigation procedures and definitions for imported cases are varied across respondents. Some countries report intra-national (from a different province or district) importation while others report only international importation (from a different country). Reactive case detection in respondent countries is defined as screening households within a pre-determined radius in order to identify other locally acquired infections, whether symptomatic or asymptomatic. Respondents report that reactive case detection can be triggered in different ways, in some cases with only a single case report and in others if a defined threshold of multiple cases occurs. The spatial range of screening conducted varies from a certain number of households to an entire administrative unit (e g, village). Some countries target symptomatic people whereas others target all people in order to detect asymptomatic infections. The majority of respondent programmes collect a range of information from those screened for malaria, similar to the range of information collected during case investigation. CONCLUSION: Case investigation and reactive case detection are implemented in the malaria elimination programmes in the Asia Pacific, however practices vary widely from country to country. There is little evidence available to support countries in deciding which methods to maintain, change or adopt for improved effectiveness and efficiency. The development and use of common evaluation metrics for these activities will allow malaria programmes to assess performance and results of resource-intensive surveillance measures and may benefit other countries that are considering implementing these activities.

Use of black carp (Mylopharyngodon piceus) in biological control of intermediate host snails of fish-borne zoonotic trematodes in nursery ponds in the Red River Delta, Vietnam.

BACKGROUND: The risks of fish-borne zoonotic trematodes (FZT) to human health constitute an important problem in Vietnam. The infection of humans with these trematodes, such as small liver trematodes (Clonorchis sinensis and Opisthorchis viverrini), intestinal trematodes (Heterophyidae) and others is often thought to be linked to fish culture in areas where the habit of eating raw fish is common. Juvenile fish produced in nurseries are often heavily infected with FZT and since fishes are sold to aquaculture facilities for growth, control of FZT in these fishes should be given priority. Controlling the first intermediate host (i.e., freshwater gastropods), would be an attractive approach, if feasible. The black carp, Mylopharyngodon piceus, is a well-known predator of freshwater snails and is already used successfully for biological control of snails in various parts of the world including Vietnam. Here we report the first trials using it for biological control of intermediate host snails in nursery ponds stocked with 1-week old fry (10-12 mm in length) of Indian carp, Labeo rohita. METHODS: Semi-field and field experiments were set up to test the effect of black carp on snail populations. In the semi-field experiment a known quantity of snails was initially introduced into a pond which was subsequently stocked with black carp. In the field trial in nursery ponds, density of snails was estimated prior to a nursing cycle and at the end of the cycle (after 9 weeks). RESULTS: The results showed that black carp affect the density of snail populations in both semi-field and field conditions. The standing crop of snails in nursery ponds, however, was too high for 2 specimens to greatly reduce snail density within the relatively short nursing cycle. CONCLUSIONS: We conclude that the black carp can be used in nursery ponds in Northern Vietnam for snail control. Juvenile black carp weighing 100 - 200 g should be used because this size primarily prey on intermediate hosts of FZT and other studies have shown that it does not prey on fish fry of other species. It may be necessary to use a high stocking density of black carp or to reduce snail density in the nursery ponds using other measures (e.g. mud removal) prior to stocking fry in order for the black carp to keep the density of intermediate host snails at a very low level.

Monitoring for Plasmodium falciparum drug resistance to artemisinin and artesunate in Binh Phuoc Province, Vietnam: 1998-2009.

BACKGROUND: Artemisinin derivatives have been used for malaria treatment in Vietnam since 1989. Reported malaria cases have decreased from 1,672,000 with 4,650 deaths in 1991, to 91,635 with 43 deaths in 2006. Current national guidelines recommend artemisinin-based combination therapy (ACT), although artesunate is still available as monotherapy through the private sector. Recent reports suggest that effectiveness of ACT and artesunate monotherapy has declined in western Cambodia. This study examined Plasmodium falciparum resistance patterns over 10 years in southwest Vietnam in infected patients treated with artemisinin compounds. METHODS: The study was conducted in two communes in Phuoc Long district, Binh Phuoc province, 100 km west of the Cambodian border. This was chosen as a likely site for emerging artemisinin resistance because of the high prevalence of P. falciparum malaria, and the length of time that artemisinin had been in use. In vivo and in vitro monitoring of P. falciparum susceptibility to anti-malarial drugs was conducted in 1998, 2001, 2004/5, and 2008/9. Patients with confirmed P. falciparum malaria received therapy with 5 or 7 days of artemisinin (1998 and 2001 respectively) or 7 days of artesunate RESULTS: In the four surveys, 270 patients were recruited and treated. The mean parasite clearance times differed between 1998, 2001 and 2004/5 (1.8, 2.3 and 2.1 days, P < 0.01) but not between 1998 and 2008/2009. The mean parasite clearance times were correlated with parasite density at day 0 (r = 0.4; P < 0.001). Treatment failure rates after PCR adjustment were 13.8%, 2.9%, 1.2%, and 0% respectively. Susceptibility of P. falciparum to artemisinin in in vitro tests was stable during the period, except for a rise in EC90 and EC99 in 2001. CONCLUSIONS: This study showed stable levels of P. falciparum sensitivity to artemisinin compounds in the two sites over a ten-year period. The introduction of ACT in this area in 2003 may have protected against the development of artemisinin resistance. Adherence to the latest WHO and Vietnamese guidelines, which recommend ACT as first-line therapy in all malarious areas, and continued monitoring along the Vietnam-Cambodia border will be essential to prevent the spread of artemisinin resistance in Vietnam.