African tick bite fever: not a spotless rickettsiosis!

Molecular Detection and Characterization of Rickettsia Species in Ixodid Ticks Collected From Cattle in Southern Zambia

Tick-borne zoonotic pathogens are increasingly becoming important across the world. In sub-Saharan Africa, tick-borne pathogens identified include viruses, bacteria and protozoa, with Rickettsia being the most frequently reported. This study was conducted to screen and identify Rickettsia species in ticks (Family Ixodidae) infesting livestock in selected districts of southern Zambia. A total of 236 ticks from three different genera (Amblyomma, Hyalomma, and Rhipicephalus) were collected over 14 months (May 2018-July 2019) and were subsequently screened for the presence of Rickettsia pathogens based on PCR amplification targeting the outer membrane protein B (ompB). An overall Rickettsia prevalence of 18.6% (44/236) was recorded. Multi-locus sequencing and phylogenetic characterization based on the ompB, ompA, 16S rRNA and citrate synthase (gltA) genes revealed the presence of Rickettsia africae (R. africae), R. aeschlimannii-like species and unidentified Rickettsia species. While R. aeschlimannii-like species are being reported for the first time in Zambia, R. africae has been reported previously, with our results showing a wider distribution of the bacteria in the country. Our study reveals the potential risk of human infection by zoonotic Rickettsia species and highlights the need for increased awareness of these infections in Zambia's public health systems.

Diagnosis and treatment of tick infestation and tick-borne diseases with cutaneous manifestations

Hard and soft ticks may be associated directly or indirectly with a number of dermatoses, both infectious and inflammatory in origin. Morbidity may occur as a result of tick bites, tick toxicosis, and even infestation. These arthropod vectors may transmit life-threatening protozoan, bacterial, rickettsial, and viral diseases with systemic and cutaneous findings. Additionally, ticks may transmit more than one pathogen with subsequent human coinfection. This article reviews the presentation of tick-borne illnesses and the medical management of these diseases. Among others, diseases such as ehrlichiosis, anaplasmosis, babesiosis, tularemia, borrelioses, tick-borne encephalitides, rickettsial spotted fevers, and tick typhus are discussed in this article. The recognition of skin manifestations associated with these diseases is paramount to early diagnosis and treatment initiation.

African tick bite fever

Physicians may encounter unfamiliar diseases as a result of international travel. Fever with rash is an important sign that usually represents initial manifestation of infectious disorders. A 62-year-old Taiwanese woman presented with multiple eschars, a papulovesicular rash, and fever 5 days after returning from South Africa. A biopsy specimen of an eschar had wedge-shaped tissue necrosis, hemorrhage, necrotizing vasculitis of the small venules and arterioles, and a dense perivascular lymphocytic infiltrate in the dermis. Serologically, there was cross reaction with both Rickettsia conorii and R. rickettsii. DNA sequencing demonstrated R. africae, confirming the diagnosis of African tick bite fever. The patient responded well to minocycline. Recognition of the symptoms and signs, and diagnostic tools for different types of rickettsiosis are essential for correct diagnosis and treatment.

Histologic features and immunodetection of African tick-bite fever eschar

Immunohistochemical detection of rickettsial antigens may be useful in diagnosis.

African tick-bite fever (ATBF) is a rickettsiosis caused by Rickettsia africae. We describe histologic features and immunodetection of R. africae in cutaneous inoculation eschars from 8 patients with ATBF, which was diagnosed by culture or association of positive PCR detection and positive serologic results. We used quantitative image analysis to compare the pattern of inflammation of these eschars with those from Mediterranean spotted fever. We evaluated the diagnostic value of immunohistochemical techniques by using a monoclonal antibody to R. africae. ATBF eschars were histologically characterized by inflammation of vessels composed mainly of significantly more polymorphonuclear leukocytes than are found in cases of Mediterranean spotted fever (p<0.05). Small amounts R. africae antigens were demonstrated by immunohistochemical examination in 6 of 8 patients with ATBF. Neutrophils in ATBF are a notable component of the host reaction, perhaps because ATBF is a milder disease than the other rickettsioses. Immunohistochemical detection of rickettsial antigens may be useful in diagnosing ATBF.

Mediterranean spotted fever: A review of fifteen cases

We aimed to determine the following things: the frequency of patients with Mediterranean spotted fever (MSF) during the last 10 years among those patients admitted with fever and rash, their clinical features, and the factors predicting the diagnosis of MSF among patients admitted with fever and rash. Between 1993-2002, the files of all patients admitted to our hospital with fever and rash were collected. The clinical features and serologic results of the patients diagnosed with MSF were further investigated. The diagnosis of MSF was established by epidemiological and clinical features and also by the clinical response within 2 days after doxycycline treatment. During the previous 10 years, 140 patients were admitted with fever and rash, and 15 (10%; four females, 11 males; mean age: 41 years; range: 17-70) of them were diagnosed with MSF. Clinical features were as follows: fever (100%), rash (100%), myalgia and/or arthralgia (93%), headache (87%), petechiae (27%), tache noire (13%), leucocytosis (74%), thrombocytopenia (33%), and accelerated erythrocyte sedimentation rate (100%). In nine of these patients, the diagnosis of MSF was established by epidemiological and clinical features and was confirmed by serologic studies. As a complication, one patient developed facial paralysis. Six (40%) were given several antibiotics. In conclusion, MSF should be considered in the differential diagnosis when a patient is admitted with fever, maculopapular rash, headache, myalgia and/or arthralgia, especially in spring, summer, or autumn.

African tick bite fever

African tick bite fever is an acute febrile illness that is frequently accompanied by headache, prominent neck muscle myalgia, inoculation eschars, and regional lymphadenitis. The disease is caused by Rickettsia africae, a recently identified spotted fever group rickettsia, which is transmitted by ungulate ticks of the Amblyomma genus in rural sub-Saharan Africa and the French West Indies. Whereas reports on African tick bite fever in indigenous populations are scarce, the number of reported cases in travellers from Europe and elsewhere has recently increased significantly. Treatment with doxycycline is associated with rapid recovery in most patients. An immunofluorescence assay is recommended for the diagnosis but seroconversion is commonly delayed and this limits the usefulness of the test. Travellers to endemic areas should be informed of the risk of contracting African tick bite fever and be encouraged to take personal protective measures against tick bites.