Temperature alters Plasmodium blocking by Wolbachia

Malaria remains one of the world’s most deadly infectious diseases, prompting research onnovel methods for controlling its spread. Many control strategies focus on targeting the mosquitoes that vector the parasites. The use of an endosymbiotic bacterium, Wolbachia, looks to be one promising approach to quell mosquito populations and limit their infectiousness, with field releases of Wolbachia-infected mosquitoes already taking place to control other vector-transmitted diseases, such as dengue fever. Laboratory experiments have already shown reduced Plasmodium pathogenicity in Wolbachia-infected mosquitos. While the mechanism underlying this interaction is yet unknown, studies investigating temperature effects on Wolbachia physiology, have shown that  certain traits associated with fitness, such as the bacteria’s replication rate  can vary with temperature. Furthermore, previous work by CIDD researchers Courtney Murdock and Matt Thomas has shown that malaria parasites and mosquito immune function can also vary with temperature. The impact of temperature on multiple factors that affect malaria transmission, including mosquito immune function, Wolbachia replication and malaria parasite prevalence, could result in intereactions that enhance or impede our ability to implement control measures. CIDD researchers Courtney Murdock, Simon Blanford, Grant Hughes, Jason Rasgon and Matt Thomas explore these interactions in a recent publication in Nature Scientific Reports. Their findings improve our understanding of how malaria control that relies on Wolbachia-infection could depend on ambient temperatures, knowledge crucial to the success of malaria control programs.

Murdock et al. investigated the effects of different temperatures on the prevalence and intensity of malaria infection in Wolbachia-infected mosquitoes,  utilizing a recently developed transinfected line of Anopholes stephensi. Their findings show markedly different establishment rates of Plasmodium across temperature treatments, with oocyst intensities highest at 24 degrees Celsius and reduced at the higher temperature of 28 degrees Celsius. Sporozoites, which are the transmissible stage of malaria parasites found in mosquito salivary glands, were found at lower densities for all temperature treatments resulting in no effect of Wolbachia infection on transmissable parasite stages at cooler temperatures, despite the enhanced oocyst establishment at 24 degrees Celsius. These results demonstrate that environmental temperature can have divergent effects on different stages of parasite development, resulting in complex effects of temperature on the ability of Wolbachia to block malaria development. Further development of this novel control technology should explore the effectiveness of pathogen blocking across diverse transmission settings.

The results were published earlier this year in Nature Scientific Reports and can be accessed here. Murdock et al.’s finding that Wolbachia limits sprozoite development is a novel new advance in malaria research and suggests promising potential for Wolbachia to mitigate malaria’s spread.