Entomological risk of African tick-bite fever (Rickettsia africae infection) in Eswatini

Abstract

Background Rickettsia africae is a tick-borne bacterium that causes African tick-bite fever (ATBF) in humans. In southern Africa, the tick Amblyomma hebraeum serves as the primary vector and reservoir for R. africae and transmits the bacterium during any life stage. Previous research has shown that even when malaria has been dramatically reduced, unexplained acute febrile illnesses persist and may be explained by the serological evidence of rickettsiae in humans. Methodology/Principal findings We collected 12,711 questing Amblyomma larvae across multiple land use types in a savanna landscape in Eswatini. Our results show that host-seeking Amblyomma larvae are abundant across both space and time, with no significant difference in density by land use or season. We investigated the entomological risk (density of infected larvae) of ATBF from A. hebraeum larvae by testing over 1,600 individual larvae for the presence of R. africae using a novel multiplex qPCR assay. We found an infection prevalence of 64.9% (95% CI: 62.1–67.6%) with no land use type significantly impacting prevalence during the dry season of 2018. The mean density of infected larvae was 57.3 individuals per 100m2 (95% CI: 49–65 individuals per 100m2). Conclusions Collectively, our results demonstrate R. africae infected A. hebraeum larvae, the most common tick species and life stage to bite humans in southern Africa, are ubiquitous in the savanna landscape of this region. Increased awareness of rickettsial diseases is warranted for policymakers, scientists, clinicians, and patients. Early detection of disease via increased clinician awareness and rapid diagnostics will improve patient outcomes for travelers and residents of this region.

When a travel bug gets you down[SS1]: severe, hypotensive African tick bite fever and response to therapy

“…Prior studies indicate that 83% of reported cases involve individuals aged between 18-64 years, 15% were 65 or older, and 2% were between 0-17 years [2]. As the primary tick-borne rickettsiosis and second most common cause of acute febrile illness after malaria in travelers returning from sub-Saharan Africa [3,4], African tick bite fever must be considered in the differential diagnosis for travelers returning from endemic areas.…”

Evidence of zoonotic rickettsiae in ixodid ticks of domestic animals in some communal farms in the Eastern Cape Province, South Africa

“…The global incidence rate of human rickettsiosis caused by R. africae has been reported to be above 5% among travelers who developed an acute febrile infection after their return from sub-Saharan Africa [ 24 ]. The presence of R. africae from A. hebraeum and species of Haemaphysalis and Rhipicephalus has long been established in South Africa [ 20 , 23 , 28 ]; hence South Africa has been described as an endemic region for ATBF.…”

Epidemiology of African Tick-Bite Fever (Rickettsia africae) in Uganda

“…They are threehost hard ticks (where each life stage completes a blood meal on a particular host before dropping off and ecdysis), they are vividly coloured (especially the males). ATBF is second only to malaria as the cause of acute febrile illness in travelers returning from sub-Saharan Africa (Freedman et al, 2006), and R. africae seropositivity rate (which is indicative of past infection) is high in indigenous populations from rural areas and could reach 60 to 90% (Ledger et al, 2022). The Rickettsia genus includes 25 validated species, 17 of which are proven human pathogens.…”