New study shows bacteria that cause African tick bite fever now infect ticks in Uganda

A new study published by researchers from the Division of Pathway Medicine at the University of Edinburgh highlights the risk of infection with Rickettsia africae for travellers to sub-Saharan Africa. 

The paper from Vincenzo Lorusso, Karolina Anna Gruszka, Ayodele Majekodunmi, Sue Welburn, and Kim Picozzi in the Division of Pathway Medicine, and their colleague Augustine Igweh at the Nigerian Institute for Trypanosomiasis Research, VOM, Jos, Plateau State, Nigeria, has just been published in the October 2103 volume of Emerging Infectious Diseases Journal

African tick bite fever

The bacteria Rickettsia africae is the causative agent of African tick bite fever (ATBF), a febrile illness of humans that can be potentially misdiagnosed with malaria.  ATBF is characterized by several flu-like symptoms such as fever, nausea, fatigue, myalgia and headache.  Since 1996, when its causative agent was first described, ATBF has gained rapidly growing importance in the field of international travel medicine, due to the increasing number of cases recorded in western safari travelers returning from sub-Saharan Africa. 

Tropical bont tick – Amblyomma variegatum

In west, central and east Africa as well as the Caribbean, R. africae is transmitted via the bite of ticks belonging to the species of Amblyomma variegatum, commonly known as the ‘tropical bont tick’ due to the typical ornamentation of its ‘cuticle’ (Figure 1).  Although preferentially feeding on domestic ruminants, as well as wildlife, this tick can accidentally parasitize humans, especially in rural areas with lush vegetation and densely populated by animal hosts (e.g., safari parks). 

L:  Male tropical bont tick Amblyomma variegatum, scale bar is 1mm; R: Sites of tick collection in Nigeria and Uganda

Tropical bont ticks have previously been shown to be vectors of R. africae in Nigeria, but prior to this study R. africae had not been detected in similar Ugandan ticks.  The aim of this new research was to determine the occurrence of R. africae DNA in A. variegatum ticks collected from cattle in Uganda and Nigeria, and assess the risk of human infection with R. africae in areas of high prevalence of the tick vector (Figure 2).  

Rickettsia africae infection of ticks discovered in Uganda

The research shows that almost half of ticks collected in Nigeria were infected with R. africae.  Strikingly the data also indicate that a large number of the Amblyomma variegatum ticks in Uganda are also now infected with R. africae bacteria.  These results highlight the risks of potential exposure to ATBF especially for those individuals dealing with cattle on a daily basis, such as farmers, veterinary and para-veterinary personnel.  In the case of Uganda, this represents the first reported presence of this pathogen in the country.  Local physicians as well as those caring for travelers returning from these areas should take ATBF into account when dealing with malaria- or flu-like symptoms.

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