Larvivorous fish for preventing malaria transmission.

BACKGROUND: Adult female Anopheles mosquitoes can transmit Plasmodium parasites that cause malaria. Some fish species eat mosquito larvae and pupae. In disease control policy documents, the World Health Organization (WHO) includes biological control of malaria vectors by stocking ponds, rivers, and water collections near where people live with larvivorous fish to reduce Plasmodium parasite transmission. In the past, the Global Fund has financed larvivorous fish programmes in some countries, and, with increasing efforts in eradication of malaria, policymakers may return to this option. Therefore, we assessed the evidence base for larvivorous fish programmes in malaria control. OBJECTIVES: To evaluate whether introducing larvivorous fish to anopheline larval habitats impacts Plasmodium parasite transmission. We also sought to summarize studies that evaluated whether introducing larvivorous fish influences the density and presence of Anopheles larvae and pupae in water sources. SEARCH METHODS: We searched the Cochrane Infectious Diseases Group Specialized Register; the Cochrane Central Register of Controlled Trials (CENTRAL), published in the Cochrane Library; MEDLINE (PubMed); Embase (Ovid); CABS Abstracts; LILACS; and the metaRegister of Controlled Trials (mRCT) up to 6 July 2017. We checked the reference lists of all studies identified by the search. We examined references listed in review articles and previously compiled bibliographies to look for eligible studies. Also we contacted researchers in the field and the authors of studies that met the inclusion criteria for additional information regarding potential studies for inclusion and ongoing studies. This is an update of a Cochrane Review published in 2013. SELECTION CRITERIA: Randomized controlled trials (RCTs) and non-RCTs, including controlled before-and-after studies, controlled time series, and controlled interrupted time series studies from malaria-endemic regions that introduced fish as a larvicide and reported on malaria in the community or the density of the adult anopheline population. In the absence of direct evidence of an effect on transmission, we performed a secondary analysis on studies that evaluated the effect of introducing larvivorous fish on the density or presence of immature anopheline mosquitoes (larvae and pupae forms) in water sources to determine whether this intervention has any potential that may justify further research in the control of malaria vectors. DATA COLLECTION AND ANALYSIS: Two review authors independently screened each article by title and abstract, and examined potentially relevant studies for inclusion using an eligibility form. At least two review authors independently extracted data and assessed risk of bias of included studies. If relevant data were unclear or were not reported, we contacted the study authors for clarification. We presented data in tables, and we summarized studies that evaluated the effects of introducing fish on anopheline immature density or presence, or both. We used the GRADE approach to summarize the certainty of the evidence. We also examined whether the included studies reported any possible adverse impact of introducing larvivorous fish on non-target native species. MAIN RESULTS: We identified no studies that reported the effects of introducing larvivorous fish on the primary outcomes of this review: malaria infection in nearby communities, entomological inoculation rate, or on adult Anopheles density.For the secondary analysis, we examined the effects of introducing larvivorous fish on the density and presence of anopheline larvae and pupae in community water sources, and found 15 small studies with a follow-up period between 22 days and five years. These studies were undertaken in Sri Lanka (two studies), India (three studies), Ethiopia (one study), Kenya (two studies), Sudan (one study), Grande Comore Island (one study), Korea (two studies), Indonesia (one study), and Tajikistan (two studies). These studies were conducted in a variety of settings, including localized water bodies (such as wells, domestic water containers, fishponds, and pools (seven studies); riverbed pools below dams (two studies)); rice field plots (five studies); and water canals (two studies). All included studies were at high risk of bias. The research was insufficient to determine whether larvivorous fish reduce the density of Anopheles larvae and pupae (12 studies, unpooled data, very low certainty evidence). Some studies with high stocking levels of fish seemed to arrest the increase in immature anopheline populations, or to reduce the number of immature anopheline mosquitoes, compared with controls. However, this finding was not consistent, and in studies that showed a decrease in immature anopheline populations, the effect was not always consistently sustained. In contrast, some studies reported larvivorous fish reduced the number of water sources withAnopheles larvae and pupae (five studies, unpooled data, low certainty evidence).None of the included studies reported effects of larvivorous fish on local native fish populations or other species. AUTHORS' CONCLUSIONS: We do not know whether introducing larvivorous fish reduces malaria transmission or the density of adult anopheline mosquito populations.In research studies that examined the effects on immature anopheline stages of introducing fish to potential malaria vector larval habitats, high stocking levels of fish may reduce the density or presence of immature anopheline mosquitoes in the short term. We do not know whether this translates into impact on malaria transmission. Our interpretation of the current evidence is that countries should not invest in fish stocking as a stand alone or supplementary larval control measure in any malaria transmission areas outside the context of research using carefully controlled field studies or quasi-experimental designs. Such research should examine the effects on native fish and other non-target species.

Larvivorous fish for preventing malaria transmission.

BACKGROUND: Adult anopheline mosquitoes transmit Plasmodium parasites that cause malaria. Some fish species eat mosquito larvae and pupae. In disease control policy documents, the World Health Organization includes biological control of malaria vectors by stocking ponds, rivers, and water collections near where people live with larvivorous fish to reduce Plasmodium parasite transmission. The Global Fund finances larvivorous fish programmes in some countries, and, with increasing efforts in eradication of malaria, policy makers may return to this option. We therefore assessed the evidence base for larvivorous fish programmes in malaria control. OBJECTIVES: Our main objective was to evaluate whether introducing larvivorous fish to anopheline breeding sites impacts Plasmodium parasite transmission. Our secondary objective was to summarize studies evaluating whether introducing larvivorous fish influences the density and presence of Anopheles larvae and pupae in water sources, to understand whether fish can possibly have an effect. SEARCH METHODS: We attempted to identify all relevant studies regardless of language or publication status (published, unpublished, in press, or ongoing). We searched the following databases: the Cochrane Infectious Diseases Group Specialized Register; the Cochrane Central Register of Controlled Trials (CENTRAL), published in The Cochrane Library; MEDLINE; EMBASE; CABS Abstracts; LILACS; and the metaRegister of Controlled Trials (mRCT) until 18 June 2013. We checked the reference lists of all studies identified by the above methods. We also examined references listed in review articles and previously compiled bibliographies to look for eligible studies. SELECTION CRITERIA: Randomized controlled trials and non-randomized controlled trials, including controlled before-and-after studies, controlled time series and controlled interrupted time series studies from malaria-endemic regions that introduced fish as a larvicide and reported on malaria in the community or the density of the adult anopheline population. In the absence of direct evidence of an effect on transmission, we carried out a secondary analysis on studies that evaluated the effect of introducing larvivorous fish on the density or presence of immature anopheline mosquitoes (larvae and pupae forms) in community water sources to determine whether this intervention has any potential in further research on control of malaria vectors. DATA COLLECTION AND ANALYSIS: Three review authors screened abstracts and examined potentially relevant studies by using an eligibility form. Two review authors independently extracted data and assessed risk of bias of included studies. If relevant data were unclear or were not reported, we wrote to the trial authors for clarification. We presented data in tables, and we summarized studies that evaluated the effects of fish introduction on anopheline immature density or presence, or both. We used GRADE to summarize evidence quality. We also examined whether the authors of included studies reported on any possible adverse impact of larvivorous fish introduction on non-target native species. MAIN RESULTS: We found no reliable studies that reported the effects of introducing larvivorous fish on malaria infection in nearby communities, on entomological inoculation rate, or on adult Anopheles density.For the secondary analysis, we examined the effects of introducing larvivorous fish on the density and presence of anopheline larvae and pupae in community water sources. We included 12 small studies, with follow-up from 22 days to five years. Studies were conducted in a variety of settings, including localized water bodies (such as wells, domestic water containers, fishponds, and pools; six studies), riverbed pools below dams (two studies), rice field plots (three studies), and water canals (two studies). All studies were at high risk of bias.The research was insufficient to determine whether larvivorous fish reduce the density of Anopheles larvae and pupae (nine studies, unpooled data, very low quality evidence). Some studies with high stocking levels of fish seemed to arrest the increase in immature anopheline populations, or to reduce the number of immature anopheline mosquitoes, compared with controls. However, this finding was not consistent, and in studies that showed a decrease in immature anopheline populations, the effect was not consistently sustained. Larvivorous fish may reduce the number of water sources with Anopheles larvae and pupae (five studies, unpooled data, low quality evidence).None of the included studies reported effects of larvivorous fish on local native fish populations or other species. AUTHORS' CONCLUSIONS: Reliable research is insufficient to show whether introducing larvivorous fish reduces malaria transmission or the density of adult anopheline mosquito populations.In research examining the effects on immature anopheline stages of introducing fish to potential malaria vector breeding sites (localized water bodies such as wells and domestic water sources, rice field plots, and water canals) weak evidence suggests an effect on the density or presence of immature anopheline mosquitoes with high stocking levels of fish, but this finding is by no means consistent. We do not know whether this translates into health benefits, either with fish alone or with fish combined with other vector control measures. Our interpretation of the current evidence is that countries should not invest in fish stocking as a larval control measure in any malaria transmission areas outside the context of carefully controlled field studies or quasi-experimental designs. Research could also usefully examine the effects on native fish and other non-target species.

Post eclosion age predicts the prevalence of midgut trypanosome infections in Glossina.

The teneral phenomenon, as observed in Glossina sp., refers to the increased susceptibility of the fly to trypanosome infection when the first bloodmeal taken is trypanosome-infected. In recent years, the term teneral has gradually become synonymous with unfed, and thus fails to consider the age of the newly emerged fly at the time the first bloodmeal is taken. Furthermore, conflicting evidence exists of the effect of the age of the teneral fly post eclosion when it is given the infected first bloodmeal in determining the infection prevalence. This study demonstrates that it is not the feeding history of the fly but rather the age (hours after eclosion of the fly from the puparium) of the fly when it takes the first (infective) bloodmeal that determines the level of fly susceptibility to trypanosome infection. We examine this phenomenon in male and female flies from two distinct tsetse clades (Glossina morsitans morsitans and Glossina palpalis palpalis) infected with two salivarian trypanosome species, Trypanosoma (Trypanozoon) brucei brucei and Trypanosoma (Nannomonas) congolense using Fisher's exact test to examine differences in infection rates. Teneral tsetse aged less than 24 hours post-eclosion (h.p.e.) are twice as susceptible to trypanosome infection as flies aged 48 h.p.e. This trend is conserved across sex, vector clade and parasite species. The life cycle stage of the parasite fed to the fly (mammalian versus insect form trypanosomes) does not alter this age-related bias in infection. Reducing the numbers of parasites fed to 48 h.p.e., but not to 24 h.p.e. flies, increases teneral refractoriness. The importance of this phenomenon in disease biology in the field as well as the necessity of employing flies of consistent age in laboratory-based infection studies is discussed.

Bis-acridines as lead antiparasitic agents: structure-activity analysis of a discrete compound library in vitro.

Parasitic diseases are of enormous public health significance in developing countries-a situation compounded by the toxicity of and resistance to many current chemotherapeutics. We investigated a focused library of 18 structurally diverse bis-acridine compounds for in vitro bioactivity against seven protozoan and one helminth parasite species and compared the bioactivities and the cytotoxicities of these compounds toward various mammalian cell lines. Structure-activity relationships demonstrated the influence of both the bis-acridine linker structure and the terminal acridine heterocycle on potency and cytotoxicity. The bioactivity of polyamine-linked acridines required a minimum linker length of approximately 10 A. Increasing linker length resulted in bioactivity against most parasites but also cytotoxicity toward mammalian cells. N alkylation, but less so N acylation, of the polyamine linker ameliorated cytotoxicity while retaining bioactivity with 50% effective concentration (EC(50)) values similar to or better than those measured for standard drugs. Substitution of the polyamine for either an alkyl or a polyether linker maintained bioactivity and further alleviated cytotoxicity. Polyamine-linked compounds in which the terminal acridine heterocycle had been replaced with an aza-acridine also maintained acceptable therapeutic indices. The most potent compounds recorded low- to mid-nanomolar EC(50) values against Plasmodium falciparum and Trypanosoma brucei; otherwise, low-micromolar potencies were measured. Importantly, the bioactivity of the library was independent of P. falciparum resistance to chloroquine. Compound bioactivity was a function of neither the potential to bis-intercalate DNA nor the inhibition of trypanothione reductase, an important drug target in trypanosomatid parasites. Our approach illustrates the usefulness of screening focused compound libraries against multiple parasite targets. Some of the bis-acridines identified here may represent useful starting points for further lead optimization.

Biolistic transformation of Schistosoma mansoni with 5' flanking regions of two peptidase genes promotes tissue-specific expression.

The gene-regulatory elements controlling peptidase expression in Schistosoma mansoni are unknown. A genomic DNA library was constructed from which 5' flanking fragments of the cathepsins F (SmCF; 649 bp) and B2 (SmCB2; 810 bp) peptidase genes were isolated. These were cloned into a GFP-expression vector for biolistic transformation of schistosomes. Both fragments promoted expression of GFP that was localised in the gut for SmCF and tegument for SmCB2, consistent with previous immunochemical data. Promoter-deletion of the SmCF gene indicated the importance of one or more transcription factor binding sites in the first 169 bp for both GFP-expression and its tissue specificity.