First detection of zoonotic Rickettsia Species in dog ticks from Malawi reveals potential public health risk

An international research team has reported the first molecular detection of Rickettsia bacteria in ticks collected from domestic dogs in Malawi, addressing a significant knowledge gap in understanding tick-borne disease risks in southeastern Africa.

The study, conducted by scientists from Hokkaido University in Japan and Lilongwe University of Agriculture and Natural Resources in Malawi, identified three species of Rickettsia—bacteria that can cause human diseases—in ticks commonly found on dogs throughout the country.

Filling a research gap

While neighboring countries like Tanzania, Mozambique, and Kenya have reported human cases of spotted fever rickettsioses, no previous study had investigated the occurrence of these pathogens in Malawi. This absence of data has made it difficult to assess the risk of rickettsial diseases in the country.

Research methodology

The researchers screened 209 blood samples from dogs and 259 tick specimens collected from four districts across Malawi between 2019 and 2020. The study combined field surveys, molecular diagnostics, and phylogenetic analysis. DNA sequencing techniques were used to detect the bacteria and to understand their genetic relationships and evolutionary history.

While no Rickettsia DNA was found in dog blood samples, the analysis revealed infection rates of 2.5% in Rhipicephalus linnaei ticks and 6.3% in Haemaphysalis elliptica ticks.

Three bacterial species identified

The study identified three distinct Rickettsia species:

• Rickettsia conorii subspecies conorii — the causative agent of Mediterranean spotted fever, which can cause serious illness in humans
• Rickettsia massiliae — known to cause mild to moderate spotted fever
• Rickettsia rhipicephali — a species with uncertain pathogenicity in humans

This marks the first detection of R. massiliae and R. rhipicephali in southern Africa, expanding the known geographical distribution of these tick-borne pathogens.

Dogs and public health

The findings are particularly relevant given the close relationship between dogs and humans in Malawi. In many households, dogs serve as working animals for security and pest control, often sharing living spaces with their owners.

Dogs can serve as sentinel animals for detecting pathogens that may affect human health, as their tick exposure patterns often reflect those of humans in the same environment.

The study found that most infected ticks were collected during the rainy season (December to March), when tick populations are highest. Dogs from urban areas showed higher tick infestation rates compared to rural dogs, possibly due to differences in animal management practices and environmental conditions.

A One Health approach

The research employed a "One Health" framework, which recognizes the interconnection between human, animal, and environmental health. This integrated approach is useful for understanding zoonotic diseases—those that can be transmitted between animals and humans.

The findings suggest that dog-associated ticks may play a role in maintaining and transmitting rickettsial pathogens with zoonotic potential, creating a possible route for disease transmission to humans. 

Conclusion

This study provides the first molecular evidence of zoonotic Rickettsia spp. in ticks collected from dogs in Malawi. The findings underscore the potential for dog-associated ticks to maintain and transmit tick-borne pathogens. An integrated surveillance approach targeting vectors, animals, and humans is critical for understanding the epidemiology of rickettsial infections in Malawi.

About the research

The study was supported in part by the Japan Society for the Promotion of Science (JSPS) KAKENHI (grant numbers JP23K23770, JP24KK0133, and JP25K02166); the Japan Agency for Medical Research and Developmen (AMED) (grant numbers JP18jm0510001 and JP23wm0225034); JST SPRING (grant number JPMJSP2119).