Efficacy of the Microbial Larvicide VectoMax^®G against <i>Anopheles gambiae</i>s.l. and <i>Culex</i>spp. Larvae under Laboratory and Open Field Trial Experiments in the City of Yaoundé, Cameroon

Background: With the rapid expansion of insecticide resistance limiting the effectiveness of insecticide-based vector control interventions, integrated control strategies associating larviciding could be appropriate to improve current control efforts. The present experimental study assesses laboratory and field efficacy of the larvicide VectoMax®G on Anopheline and Culicine larval stages in Yaoundé. Methods: The effect of the larvicide VectoMax®G, a combination of Bacillus thuringiensis var. israelensis (Bti) and Bacillus sphaericus (Bs), on larval development was assessed during both laboratory and open field trial experiments. Laboratory experiments permitted the evaluation of five different concentrations with four replicates/experiments. Laboratory experiments were conducted with Anopheles coluzzii “Ngousso” and Culex quinquefasciatus laboratory strains. Open field trials were conducted using sixteen plastic containers with a diameter of 0.31 m buried in an array of four rows with 4 containers each. Distance between rows and between containers in a row was 1 meter. This experiment permitted to test the effect of the microbial larvicide VectoMax®G under operational application conditions on field mosquito populations. Results: The time to induce 100% mortality after exposure to serial concentrations of the larvicide varied according to the dose from 4 - 12 hours for An. coluzzii and 6 - 9 hours for Cx. quinquefasciatus in laboratory experiments. Measurements of the residual activity indicated that all VectoMax®G concentrations were still active after 35 days and killed 86% - 100% of larvae. Lethal dose of VectoMax®G killing 50% of larvae was estimated at 5.24 × 10-8 mg/m2 for An. coluzzii and 1.25 × 10-8 mg/m2 for Cx. quinquefasciatus. The lethal concentration inducing 95% mortality was estimated at 3.13 × 10-7 mg/m2 for An. coluzzii and 2.5 × 10-8 mg/m2 for Cx. quinquefasciatus. Open field trials tests indicated that sub-lethal concentrations of VectoMax®G successfully killed 100% An. gambiae s.l. larvae within 24 hours, while with Culex spp. larvae, 100% mortality was recorded after 48 hours post-treatment. Natural recolonization of water containers by larvae was recorded between 3 and 6 days respectively after the treatment with sublethal doses. Late instar larvae were recorded 5 and 6 days after treatment. When the jars were treated with reference dosage or supra doses of VectoMax®G, recolonization of water containers was observed six days after treatments. No pupae of both species were found 6 and 7 days post-treatment. Conclusions: The study indicated high efficacy of the microbial larvicide VectoMax®G against Anopheline and Culex larvae. Microbial larvicides such as VectoMax®G could be appropriate for controlling mosquito population particularly in areas experiencing high insecticide resistance or outdoor biting mosquitoes.

Laboratory Growth of <i>Anopheles gambiae</i>(Diptera: Culicidae) and Morphological Determinism of Moulting

Growth in arthropods in general and in insects in particular, is supposed to be discontinuous and occurs during moulting. In Culicidae in general and Anopheles in particular, the number of moults is five with the fourth which gives the pupae. It is known that moulting in insects is a genetic and physiological phenomenon. Most physiological reactions are triggered by chemical or physical stimuli. The pressure exerted by the growth of the larval body on the exocuticle is one of the triggers of moulting. The objective of this work was therefore to determine the exact timing of the first three moults that determine the growth of An. gambiae larvae from egg hatch to pupation to highlight the role of increased larval size in the stimulation of moulting. We therefore, undertook to rear larvae of this anopheline species in the laboratory under conditions close to their natural environment from hatching to pupation. The length and width of the head, thorax and abdomen were recorded daily. Data analysis showed that the size of the head and thorax remained constant for the first three days (D0 to D2) of development and abdomen’s length for the first two days and then increased daily until day seven (D7) when it stopped. These observations led us to say that the M1 moult occurs at end of the third day of development and the M3 moult at end of the eighth day;the M2 moult could not be determined. All these observations led to the conclusion that the larval growth of An. gambiae has a continuous regimen and the growth of the head and thorax of the larva plays a crucial role in the onset of moulting.

First report on molecular characterization of Leishmania species from cutaneous leishmaniasis patients in southern Khyber Pakhtunkhwa province of Pakistan

Objective: To report presence of Leishmania major in Khyber Pakhtunkhwa of Pakistan, where cutaneous leishmaniasis(CL) is endemic and was thought to be caused by Leishmania tropica only. Methods: Biopsy samples from 432 CL suspected patients were collected from 3 southern districts of Khyber Pakhtunkhwa during years 2011–2016. Microscopy on Giemsa stained slides were done followed by amplification of the ribosomal internal transcribed spacer 1 gene. Results: Leishmania amastigotes were detected by microscopy in 308 of 432 samples(71.3%) while 374 out of 432 samples(86.6%) were positive by ribosomal internal transcribed spacer 1 PCR. Subsequent restriction fragment length polymorphism confirmed Leishmania tropica in 351 and Leishmania major in 6 biopsy samples. Conclusions: This study is the first molecular characterization of Leishmania species in southern Khyber Pakhtunkhwa. It confirmed the previous assumptions that anthroponotic CL is the major CL form present in Khyber Pakhtunkhwa province. Furthermore, this is the first report of Leishmania major from a classical anthroponotic CL endemic focus identified in rural areas of Kohat district in southern Khyber Pakhtunkhwa.

Knowledge of Healthcare Workers Regarding Dengue and Chikungunya in Some Health Facilities of the City of Yaoundé(Cameroon) and Its Neighbourhood

Background: Good knowledge of diseases’ epidemiology, diagnostic methods and treatment schemes are critical for early detection and effective management of dengue and chikungunya outbreaks. Here, we assessed knowledge and practices regarding dengue and chikungunya among health care workers of some health facilities of Yaoundé and its surroundings. Methods: A descriptive cross-sectional study was conducted from January to August 2020 in 35 health facilities of Yaoundé and its surroundings. Structured pre-tested questionnaire including 11 questions was used to assess healthcare workers’ (i) knowledge on dengue and chikungunya (pathogen, mode of transmission, signs and symptoms) and, (ii) management practices (diagnosis, prevention and treatment measures). Face to face interviews were conducted with healthcare workers including medical doctors, nurses, medical assistants and laboratory assistants. Findings: A total of 232 healthcare workers were interviewed. Despite that 40.95% (n = 95) of respondents had heard about dengue and chikungunya, only 4.74% (n = 11) of them were aware of the fact that both diseases are caused by virus. Also, 9 out of 232 (3.88%) knew that these diseases were transmitted by the bite of an Aedes mosquito. About 15.52% (n = 36) were able to give at least 1 clinical symptom related to dengue and chikungunya. The main diagnostic method they knew was Polymerase Chain Reaction (3.02%;n = 7). For prevention, many participants indicated vector control by using insecticide treated bednets or destroying potential breeding sites (14.23%;n = 33). Only few participants 3.88% (n = 9) knew how to manage dengue or chikungunya cases. To improve the management of both diseases, a significant proportion of healthcare workers (37.93%;n = 88) reported being in need of additional training. Conclusion: The poor knowledge regarding dengue and chikungunya among healthcare workers in Yaoundé and its neighbourhood raises the need to intensify sensitization campaigns and training activities towards this personnel.