Evaluation of the « Time/Risk » Probability of being Infected and its Evolution Before/After a Long Term Village Scale Malaria Vector Control Programme in Angola

Three main entomological indicators are classically used in the epidemiology of malaria: the inoculation rate (“h”) of Ross, the vectorial capacity (“C”) of Garrett-Jones and the reproduction rate (“z”) of Macdonald. In spite of their undoubtfully usefulness it appeared that their formulae did not integrate the key parameter of “t” i.e. the time of exposure and therefore the probabilities of being infected according to the entomological condition (density, infectivity, longevity of the vectors) but also the time/risk and the reduction of this risk when some village-scale vector control measures are implemented. To deal with this approach we used the Briley’s formula, elaborated some years ago, to analyze the time/risk of being infected in the framework of a long term village scale vector control programme implemented around Balombo (Benguela Province, Angola) with classical method (inside residual spraying) and newly developed tool s (insecticide treated plastic sheeting) used alone or in association with the classical long lasting insecticide treated nets. Before vector control the risk was almost 20% in one week, 60% in one month and 100% in 3 months and this explain why plasmodic index are so high in this area without any organized vector control programme. The 3 methods actually reduced the risks which become of the order of 2% in one week, 10% in one month, 26% in one trimester but 70% in one year; the three methods had the same efficacy in reducing these risks. The fact that the risk reach 70% in one year even with right vector control shows the needs of renewing regularly the operations, the needs of other than entomological methods of prevention but also that immunity could be maintained and feared “rebound” was not observed even during the long term of the programme.

Biting Pattern and Seasonality of Filariasis Vector of Mansonia spp. in Endemic Area of Banyuasin Regency, South Sumatera, Indonesia

The diversity and biting activity of Mansonia is important to be determined as to predict the incriminated vector and pattern the mosquito behaviour in establishing the vector control programme. The present study has been successfully conducted to investigate the prolonged biting behaviour of Mansonia spp. in two villages in Banyuasin Regency, South Sumatera Province-Indonesia, using Human Landing Collection method (HLC) in indoor and outdoor for 14 months. The result shows that there are 4956 Mansonia spp. mosquitoes collected during the study comprising 6 species: Mansonia uniformis (40.37%), Mansonia annulifera (32.04%), Mansonia indiana (19.97%), Mansonia bonneae (5.28), Mansonia dives (2.14%); and Mansonia annulata (0.18%). The further investigation confirms that Mansonia uniformis (41.254%) and Mansonia bonneae (45.490%) become the most dominant species caught in Sedang village and Muara Sugih village, respectively and find higher biting activities in outdoor than indoor with biting peaked time at approximately 18.00-19.00. However, the biting activities is also observed in daytime, indicating the behaviour change of Mansonia spp. as the nocturnal mosquitoes. Furthermore, the periods of the highest biting rates are found in April 2017 and May 2017 in Sedang village and May 2018 in Muara Sugih Village. The high period of biting activities and behaviours become the valuable information to arrange the further controlling action of filariasis transmission in Sedang and Muara Sugih Villages as the endemic area of filariasis in South Sumatera, Indonesia.

Status of Insecticide Resistance of Malaria Vector Anopheles stephensi towards Insecticides in Alwar District of Rajasthan, India

Pyrethroids have been developed as a powerful insecticide that is widely used for space spray and residual indoor spraying, with impregnated nets included in the vector control programme. Insecticide resistance reduces the effectiveness of pesticides. Therefore, the vector susceptibility condition of the Anopheles stephensi is monitored in order to select the active ones. The current study is being conducted in a malaria-ridden area in various parts of the Alwar region of Rajasthan, India, against the malaria vector An. stephensi. The Susceptibility study was conducted by the WHO standardized method using the diagnostic doses of DDT, Alpha-cypermethrin and Deltamethrin. An. stephensi showed intermediate resistance to DDT from all over the study while susceptible to Alpha-cypermethrin and Deltamethrin.

Pilot Suppression trial of Aedes albopictus mosquitoes through an Integrated Vector Management strategy including the Sterile Insect Technique in Mauritius

It is often difficult to control the vector mosquito Aedes albopictus using conventional chemical control methods alone at an operational level mainly because of (1) the ability of the species to lay eggs in a variety of places which are often difficult to detect or access by larviciding operators, (2) the inherent tendency of adults to live and feed outdoor which makes them unlikely targets of Insecticide Residual Spraying and (3) the development of resistance to insecticides by the species. It is therefore necessary for countries to investigate alternative control methods (such as the Sterile Insect Technique (SIT)) that can be integrated in their national vector control programme in order to address those limitations.In this field trial, mass-produced, radio-sterilized Ae. albopictus males could successfully compete with wild males in a small village in Mauritius. Our study also demonstrated that within specific eco-climatic conditions, SIT can be used as a suppression tool against Ae. albopictus and, unlike numerous chemical control methods, effectively maintain the suppression level when the latter is found at low densities. Finally, the need for mosquito SIT programmes to develop contingency plans against increasingly frequent extreme weather occurrences was also highlighted.

“House Plasmodial Prevalence Index” Another Relevant Indicator of Evaluating a Malaria Vector Control Operations, Example of Capango Village (Benguela Province, Angola)

The WHO fascicule “Information systems for the evaluation of malaria control programmes” identified as outcome target “the proportion of households targeted for use of nets using at least one impregnated bednet” [1]. The parasitological evaluation of the efficacy of vector control programme is mainly based on the plasmodial prevalence rate evaluated by cross sectional or longitudinal surveys on representative sample of the human population targeted. For the new “House plasmodial” index we decided to combine the 2 indicators: the classical human plasmodial prevalence and house considering as positive any house with “at least one symptomless inhabitant having at least one positive thick film during the survey”. We used this new indicator when analyzing data gained during 24 regularly done parasitological surveys during 5 years in Capango village where a vector control (VC) programme was implemented using both Long Lasting Nets PermaNet© 2.0 and deltamethrin treated wall lining called ZeroFly© inside every house. Surveys were done during 2 years before VC and 3 years after. It appeared that the House Plasmodial positive index showed the same trends and level as the classical human plasmodial prevalence and clearly indicated the impact of vector control in reducing the overall plasmodial prevalence in the targeted village. On the other hand it appeared repeating surveys identified “frequently positive houses” (=found positive in some 50% of surveys) and therefore to be prioritized for control and those “scarcely positive” (20% of surveys). The House Plasmodial Prevalence index appeared relevant and reliable, interesting to be used in vector control programme while easy to get and should be considered in other epidemiological situation.

Small-scale field assessment of efficacy of the autodissemination approach against Aedes sp. in an urban area

This is the first study to evaluate the efficacy of an autodissemination approach, as suggested by WHO. Therefore, the efficacy of an autodissemination approach in small-scale field trials against wild Aedes sp. population was evaluated in an urbanized setting, Malaysia. Lethal ovitraps enhanced with pyriproxyfen were used to control Aedes sp. populations at treatment sites, with the autodissemination activity was assessed using the WHO larval bioassays. Lethal ovitraps enhanced with pyriproxyfen effectively reduced of Aedes sp. population. All autodissemination stations were shown to be visited by Aedes sp. mosquitoes with 100% complete inhibition against eggs and larvae development. In the larvae bioassay, pupae mortality ranged from 14 to 40%. Statistically, a significant reduction of Aedes sp. population in the treatment sites compared to the untreated areas. The study proved for the autodissemination of pyriproxyfen to breeding habitats by wild Aedes sp. This technique is highly potentially for vector control activities. Future evaluation should focus on large-scale field trials.Author SummarySince 2012, Dataran Automobil, Seksyen 15, Shah Alam, was declared as one of the dengue hotspot areas. Major vector control activities were conducted by government, NGOs, social communities, and local authorities, but the number still rising. We conducted a new invention of autodissemination concepts in this area by an entomological study on mosquito populations reduction and dispersal abilities of the technique. We found that the technique has proven to control mosquito populations, but the other factors such as epidemiology link still unclear and need further clarification. Our finding highlighted the effectiveness of autodissemination strategies that can be considered as one of the alternative tools in vector control programme.

Species Composition and Role of Anopheles Mosquitoes in Malaria Transmission Along Badagry Axis of Lagos Lagoon, Lagos, Nigeria

Three communities along Badagry axis of the Lagos lagoon were sampled for indoor resting Anopheles mosquitoes in order to determine their species composition, relative abundance, density and contribution to malaria transmission in the coastal ecosystem. A total of 1938 adult female Anopheles mosquitoes collected from 2005 to 2007 constituted three species viz Anopheles gambiae, An melas and An. nili. The Polymerase Chain Reaction (PCR)–-based tests indicated that more than three-fourth of the An. gambiae s.l (75.8%) population belongs to An. gambiae s.s the remaining were An. melas. Further analysis showed that all the An. gambiae s.s was the M form. ELISA-based analyses indicated that An. gambiae s.s and An. melas were the main vectors of malaria in this area with an overall P. falciparum sporozoite infection rate of 4.8% and 6.5% respectively. Both species also maintained relatively high EIR indicating their prominent roles in malaria transmission in the study area. All the An. nili tested were negative for P. falciparum sporozoite infection. This study provides baseline information for planning vector control programme relevant to reduction of malaria transmission in the coastal areas of Nigeria.