https://www.cell.com/trends/parasitology/pdf/S1471-4922(11)00083-3.pdf

Microbiome influences on insect host vector competence

Bacterial diversity of field-caught mosquitoes, Aedes albopictus and Aedes aegypti, from different geographic regions of Madagascar.

Many infections can be transmitted between animals and humans. The epidemiological roles of different species can vary from important reservoirs to dead-end hosts. Here, we present a method to identify transmission cycles in different combinations of species from field data. We used this method to synthesise epidemiological and ecological data from Bipindi, Cameroon, a historical focus of gambiense Human African Trypanosomiasis (HAT, sleeping sickness), a disease that has often been considered to be maintained mainly by humans. We estimated the basic reproduction number [Formula: see text] of gambiense HAT in Bipindi and evaluated the potential for transmission in the absence of human cases. We found that under the assumption of random mixing between vectors and hosts, gambiense HAT could not be maintained in this focus without the contribution of animals. This result remains robust under extensive sensitivity analysis. When using the distributions of species among habitats to estimate the amount of mixing between those species, we found indications for an independent transmission cycle in wild animals. Stochastic simulation of the system confirmed that unless vectors moved between species very rarely, reintroduction would usually occur shortly after elimination of the infection from human populations. This suggests that elimination strategies may have to be reconsidered as targeting human cases alone would be insufficient for control, and reintroduction from animal reservoirs would remain a threat. Our approach is broadly applicable and could reveal animal reservoirs critical to the control of other infectious diseases.

/pdf/identifying-transmission-cycles-at-the-human-animal-200tw94pat.pdf

Identifying Transmission Cycles at the Human-Animal Interface: The Role of Animal Reservoirs in Maintaining Gambiense Human African Trypanosomiasis

The viviparous tsetse fly utilizes proline as a hemolymph-borne energy source. In tsetse, biosynthesis of proline from alanine involves the enzyme alanine-glyoxylate aminotransferase (AGAT), which requires pyridoxal phosphate (vitamin B6) as a cofactor. This vitamin can be synthesized by tsetse's obligate symbiont, Wigglesworthia glossinidia. In this study, we examined the role of Wigglesworthia-produced vitamin B6 for maintenance of proline homeostasis, specifically during the energetically expensive lactation period of the tsetse's reproductive cycle. We found that expression of agat, as well as genes involved in vitamin B6 metabolism in both host and symbiont, increases in lactating flies. Removal of symbionts via antibiotic treatment of flies (aposymbiotic) led to hypoprolinemia, reduced levels of vitamin B6 in lactating females, and decreased fecundity. Proline homeostasis and fecundity recovered partially when aposymbiotic tsetse were fed a diet supplemented with either yeast or Wigglesworthia extracts. RNA interference-mediated knockdown of agat in wild-type flies reduced hemolymph proline levels to that of aposymbiotic females. Aposymbiotic flies treated with agat short interfering RNA (siRNA) remained hypoprolinemic even upon dietary supplementation with microbial extracts or B vitamins. Flies infected with parasitic African trypanosomes display lower hemolymph proline levels, suggesting that the reduced fecundity observed in parasitized flies could result from parasite interference with proline homeostasis. This interference could be manifested by competition between tsetse and trypanosomes for vitamins, proline, or other factors involved in their synthesis. Collectively, these results indicate that the presence of Wigglesworthia in tsetse is critical for the maintenance of proline homeostasis through vitamin B6 production.

Vitamin B6 Generated by Obligate Symbionts Is Critical for Maintaining Proline Homeostasis and Fecundity in Tsetse Flies

Tsetse flies are the primary vectors of African trypanosomes, which cause Human and Animal African trypanosomiasis in 36 countries in sub-Saharan Africa. These flies have also established symbiotic associations with bacterial and viral microorganisms. Laboratory-reared tsetse flies harbor up to four vertically transmitted organisms - obligate Wigglesworthia, commensal Sodalis, parasitic Wolbachia and Salivary Gland Hypertrophy Virus (SGHV). Field-captured tsetse can harbor these symbionts as well as environmentally acquired commensal bacteria. This microbial community influences several aspects of tsetse’s physiology, including nutrition, fecundity and vector competence. This review provides a detailed description of tsetse’s microbiome, and describes the physiology underlying host-microbe, and microbe-microbe, interactions that occur in this fly.

/pdf/tsetse-fly-microbiota-form-and-function-1h9rotgvk6.pdf

Tsetse fly microbiota: form and function.

http://www.sleeping-sickness.ird.fr/pdf/00547.pdf

Tripartite interactions between tsetse flies, Sodalis glossinidius and trypanosomes--an epidemiological approach in two historical human African trypanosomiasis foci in Cameroon.

In Cameroon, since the first epidemiological week held in 2015, snakebites have been registered among Potential Epidemic Diseases (PED). In the Centre Region, the most densely populated of the country, weekly reports of snakebites are generated at health districts level for monthly data updates. To contribute to the better management of snakebite cases, an observational study was conducted to assess the snakebite reporting rate in the Centre Region of Cameroon. The results of this retro-prospective survey were confronted to those of the weekly epidemiological surveillance system, recorded in the PED regional data base. The incidence of bites was relatively high (36.6 bites per 100,000 inhabitants), as well as the general attack rate (about 49 envenomations per 100 victims). The lethality recorded was 2.5% and the mortality was about 1 death per 100,000 inhabitants a year. The sex ratio was largely female biased (61.6%). The bites occurred mostly during the rainy season (73.0%). Bitten victims were mainly farmers (47.4%), and agriculture was the main risk factor. The comparative analysis of the data suggested a high non-reporting rate of snakebite cases (67.8%). Snakebite is an endemic condition in the Centre Region of Cameroon. Because of the high rate of non-reporting of cases, the collection of information from the registers of the health facilities only appears not enough to assess the real importance of envenomation in this Region.

/pdf/high-snakebite-underreporting-rate-in-the-centre-region-of-3seh37c7oe.pdf

High snakebite underreporting rate in the Centre Region of Cameroon: an observational study.

Progress towards global elimination of lymphatic filariasis.

The severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is responsible for the development of a highly contagious disease called coronavirus disease (COVID-19). Ten months after the onset of the pandemic, America and Europe remain the most affected regions. Initially, experts predicted that Africa, the poorest continent with the most vulnerable population and health system, would be greatly affected by the ongoing outbreak. However, 240days after the first confirmed case, Africa is among the least affected region, with lower than expected incident cases and mortality. In this review, we discuss possible explanations and reasons for this unexpected low burden of COVID-19 in Africa. We focus on the characteristics of the virus, specificities of the sub-Saharan African population and local environment.

Unexpected low burden of coronavirus disease 2019 (COVID-19) in sub-Saharan Africa region despite disastrous predictions: reasons and perspectives

Background: Depression of the immune system caused by the human immunodeficiency virus (HIV) promotes the onset of opportunistic infections including intestinal parasites. Objectives: In this study, we are comparing the prevalence of these parasitic infections among individuals infected with HIV (HIV+) and non-infected (HIV-) enrolled in four HIV care units in the Centre Region of Cameroon. Methods: A cross-sectional study was conducted and stool samples were collected from 283 HIV positive subjects and 245 seronegative subjects. These samples were processed using direct wet mount, formol-ether concentration, Kato-Katz procedure, modified Ziehl-Neelsen staining, and Baermann techniques to identify both common and opportunistic intestinal parasites. Logistic regression analyses were used to assess the association between HIV infection and socio-demographics factors as well as infection with intestinal parasites. Results: A total of 123 (23.4%) individuals were found infected with at least one protozoan parasite species, and nine (1.7%) with intestinal worms. Overall, infection rates were 27.9% and 22.4% among HIV+ and HIV- subjects, respectively. The frequencies of Cryptosporidium spp. and Entamoeba histolytica/dispar were significantly more important among HIV+ subjects (P < 0.0455). Pentatrichomonas hominis and Entamoeba coli were significantly more prevalent among HIV- subjects (P < 0.0210). Heterogeneity was observed in the distribution of intestinal parasites, according to socio-demographic parameters. In addition, Cryptosporidium spp. was significantly associated with the decrease in CD4 cell count (P = 0.0035). The frequencies of infections with Cryptosporidium spp., Isospora belli, and Iodamoeba buetschlii were significantly more important in HIV positive patients not taking antiretroviral (P < 0.0226). Conclusions: Cryptosporidium spp., Entamoeba histolytica/dispar, and Blastocystis spp. were the intestinal pathogens more often found among HIV infected individuals. HIV positive subjects were significantly more infected with intestinal parasites than seronegatives in intermediate and rural settings, among individuals aged more than 45 years and among unemployed individuals.

Prevalence of Intestinal Parasitic Infections in Relation to the HIV Status of Patients Attending the Care Units in Three Divisions in the Centre Region of Cameroon

Hugues Nana Djeunga

Papers

Tripartite interactions between tsetse flies, Sodalis glossinidius and trypanosomes--an epidemiological approach in two historical human African trypanosomiasis foci in Cameroon.

High snakebite underreporting rate in the Centre Region of Cameroon: an observational study.

Progress towards global elimination of lymphatic filariasis.

Unexpected low burden of coronavirus disease 2019 (COVID-19) in sub-Saharan Africa region despite disastrous predictions: reasons and perspectives

Prevalence of Intestinal Parasitic Infections in Relation to the HIV Status of Patients Attending the Care Units in Three Divisions in the Centre Region of Cameroon