A multidisciplinary approach to study virulence of the entomopathogenic fungus Beauveria bassiana towards malaria mosquitoes

Abstract

A multidisciplinary approach to study virulence of the entomopathogenic fungus Beauveria bassiana towards malaria mosquitoes. Malaria diseaseMalaria is a vector-borne disease that causes a great threat to human health. The disease is present throughout the tropics, especially in sub-Saharan Africa. Around 214 million cases were reported in 2015, with an estimated mortality of 438 thousand people in 2014 (World Health Organization, 2015). Of these, around 70% where children under five years of age. Malaria is caused by parasites of the Plasmodium genus, most cases being caused by P. falciparum or P.vivax, and to a lesser extent by P. ovale, P. malariae, and P. knowlesi (White et al., 2014). Malaria parasites are transmitted by female mosquitoes of the genus Anopheles, but only 70 to 80 of more than 480 Anopheles species are able to do so (Manguin et al., 2008). Mosquitoes of the An. gambiae complex are considered the main vectors of human malaria in Africa and the complex is composed of eight species, namely: An. gambiae s.s., An. arabiensis, An. quadriannulatus, An. melas, An. merus, An. bwambae, An. coluzzii and An. amharicus (Coetzee, 2004; Coetzee et al., 2013).Malaria transmission is initiated when an infected female Anopheles mosquito inoculates sporozoites into the subcutaneous tissue of a human host while blood-feeding. From there, sporozoites travel to the liver, where they undergo several transformations and eventually develop into thousands of merozoites. Once merozoites are released in the blood stream, they infect red blood cells and reproduce asexually. A small amount of asexual parasites develops into gametocytes that may be ingested by an Anopheles mosquito during a blood meal (Miller et al., 2002). Gametocytes reproduce sexually inside the mosquito, developing into a motile ookinete that migrates through the midgut wall, and becomes an oocyst on the mosquito's midgut.The oocyst grows and bursts, releasing sporozoites, which move to the salivary glands of the mosquito. When a mosquito takes a new blood meal, it will infect a new host, thereby repeating the infection cycle (White et al., 2014). Malaria controlPresently, the main interventions to control and eliminate malaria are vector control (stop mosquitoes of infecting malaria), chemoprevention (suppression and prevention of infections) and case management (diagnosis and treatment of infections) (World Health Organization, 2015). Currently, the most effective way of eradicating and preventing malaria is achieved by vector control using insecticides (Raghavendra et al., 2011). This is accomplished through the use of Insecticide-Treated bed Nets (ITNs) and/or through Indoor Residual Spraying of insecticides (IRS). ITNs provide a physical and chemical barrier against mosquitoes and can reduce the incidence of malaria transmission, especially since most malaria mosquitoes have a nocturnal biting behaviour. ITNs are coated with pyrethroids that have a very low toxicity to 9 mammals, a rapid knock-down effect, and long residual activity (R...