Spotted fever group
Rickettsioses are vector-borne diseases of medical importance, particularly in African countries where an increasing number of cases have been reported amongst residents and tourists [
In Angola, a high percentage of the population lives in suburban neighbourhoods, characterized by adobe and cement constructed houses with limited access to public basic resources such as potable water, energy supply, health, and education. These highly unhealthy living conditions associated with domestic animals in close proximity increase the exposure to ectoparasites and to the pathogens that they might harbour.
Many studies report rickettsioses acquired by travellers, but the majority refers to sub-Saharan Africa tourists who develop African tick-bite fever (ATBF) [
The aim of this study was to perform the laboratory diagnosis of
Between February 2016 and March 2017, a total of 87 serum specimens were obtained from public hospitals, as part of the Febrile Syndrome Surveillance Programme of Angola. These serum specimens were collected from patients from different cities (Benguela, Cabinda, Huambo, Luanda, and Malanje) and provinces (Huíla, Kwanza Sul, Kwanza Norte, Lunda Norte, and Zaire) of Angola and were selected for this study if belonging to individuals presenting fever for at least four days (≥37.5°C) and with at least one of the following inclusion criteria: malaise, myalgia, arthralgia, nausea, vomiting, and rash. These selected serum specimens were also malaria and yellow fever negative, previously tested through peripheral blood smear, malaria antigen detection test (SD BIOLINE), and RT-PCR, respectively.
A questionnaire including patient demographic (age and gender) and epidemiological data (province and municipality of origin, type of residence, household characteristics, season of specimen collection, access to potable water, contact with animals, and clinical manifestations) was filled for each patient by the health care professionals.
Sera were tested by an in-house immunofluorescence assay (IFA) using
A total of 87 patients from 10 different cities and provinces were analysed in this study (Figure
Study area with Angola sampling location cities (Benguela, Cabinda, Huambo, Luanda, and Malanje) and provinces (Huíla, Kwanza Sul, Kwanza Norte, Lunda Norte, and Zaire).
Of all sera from febrile patients of Angola analysed (
Rickettsioses are rarely considered when evaluating patients with undifferentiated febrile illnesses, and due to the overlapping symptomatology with other endemic diseases such as malaria, dengue, and yellow fever, diagnosis is difficult without confirmatory laboratory tests.
Our study aimed at ascertaining the association of
The IFA is currently the gold standard test for serological diagnosis of
This study has detected three
Interestingly, these results are similar to a study reported by Botros and collaborators [
Despite the important message that our results may arouse regarding a possible
The transmission and dissemination of rickettsiae through vectors are a phenomenon of growing concern with the expanding human populations and increasing contact between humans and animals (domestic and wildlife) [
The rickettsiae-exposed patients who participated in our study lived in urban zones of Benguela and Luanda cities. One of them is a student, and the other two street vendors. A previous study done in pet dogs from Luanda [
Although in a low prevalence, this finding is relevant to the clinical management of patients with fever of unknown origin and support the inclusion of this VBD in clinical diagnostic algorithms.
To conclude, our findings suggest that rickettsioses are present in Angola and, therefore, should be taken into account in cases of febrile illness. The serological evidence of exposure with these bacteria raises attention for the need of appropriated public health interventions and diagnostic improvement. Forthcoming studies should include a higher specimen number, with the possibility of detecting the pathogen in acute infection phases, both acute and convalescent samples screening, antibodies testing against several antigens, and, if possible, application of molecular techniques in skin biopsy or swab samples from suspected cases with eschar. This will allow the identification of risk factors and the establishment of prevention and control disease strategies for
African tick-bite fever
Immunofluorescence assay
Immunoglobulin
Spotted fever group
Reverse transcription polymerase chain reaction.
Data used to support the findings of this study are available from the corresponding author upon request.
This study was approved by the ethics committee at the National Institute of Public Health, Ministry of Health, Angola, under the authorization number 38/2017 as part of the laboratory surveillance of febrile syndromes.
Adults and parents or legal guardians of children participating in this study authorized and provided written informed consent for this investigation and sample collection.
The authors declare that they have no conflicts of interest.
P. Barradas (SFRH/BD/116449/2016) acknowledges the Portuguese Foundation for Science and Technology (FCT) for financial support. IPATIMUP integrates the i3S Research Unit, which was partially supported by FCT. This work was funded by FEDER Funds Through the Operational Programme for Competitiveness Factors-COMPETE and National Funds through the FCT, under the project number PEst-C/SAU/LA0003/2013. This paper was published under the framework of the European Social Fund, Human Resources Development Operational Programme (2007–2013) (POSDRU/159/1.5/S/136893). The authors would like to thank Dr. Joana de Morais, INIS, for supporting this work and all the surveillance technicians involved in sample collection.