RésuméBrucellosis is seen as a neglected zoonosis that affects a wide variety of species. This research focuses on a South African “One Health” setting where there are wildlife, domestic animals and humans existing in close proximity. There are five studies to this research, the first is a systematic review of brucellosis in wildlife in Africa, which revealed that evidence for Brucella infection was found serologically in sixty-one wildlife species and identified the Brucella species (Brucella abortus, Brucella melitensis, Brucella suis and Brucella inopinata).
This research then took an in-depth look into the epidemiology of the Brucella infection at a human, domestic animal and wildlife interface in Eastern South Africa in a site that we saw as an example of a communal livestock ranching setting in the proximity of wildlife in Africa. Besides B. abortus infection, we identified B. melitensis infection in buffalo (Syncerus caffer) in the Kruger National Park. Yet, we found low serological evidence of infection cattle and goats and none in dogs and humans. The goats were deemed to not be infected by confirmatory tests (indirect enzyme-linked immunosorbent assay (iELISA) and brucellin skin test). The dogs were all classified negative by the RBT. The cattle were found to have a low serological prevalence (1.4%), decreasing serology with age and significantly less males positive than females, which is not indicative of a wildtype B. abortus infection. This indicated the serological positives could be due to residual vaccine antibodies, which was supported by our inability to identify the organism when doing further focused testing with serology, brucellin skin test and culture.
This led us to conduct a longitudinal cohort study to investigate the immune response to the state regulated “high dose” Strain 19 vaccination of heifers between 4 – 8 months.
We found a comprehensive and rapid serological response that peaked at 2 weeks for Rose-Bengal test (RBT) and 10 weeks for indirect Enzyme-Linked Immunosorbent Assay (iELISA). The response declined more sharply with RBT compared to iELISA (5% RBT positive and 17% iELISA positive between 10 and 14 months after vaccination). We found evidence of an immunological response four and a half years after vaccination. This serological persistence can, as hypothesized, interfere with disease control methods using serology for identification of infected animals. To reduce the risk of cross-reaction with disease surveillance and given the low incidence observed, a more appropriate vaccination method for this setting maybe a “low dose” or a subconjunctival means of administration, although it could be challenging to restrain heifers sufficiently in this setting for this type of administration.
These research outcomes are of significant relevance to disease control authorities trying to focus limited resources on brucellosis control in similar settings. The infected wildlife in close proximity is a risk to both humans and domestic animals. The identification of B. melitensis for the first time in buffalo in Africa is of significance as this suggests a spillover from a reservoir species, most likely small stock species, although it could have been from another unknown infected wildlife species. Yet, we found that the domestic animals and therefore their products at this site were free of Brucella infection and thus currently not a risk to the humans. Our research showed the effectivity of the vaccination program in eliciting an immune response in this African “One Health” setting, suggesting that the induced herd immunity would protect animals in the case of the introduction of a wild type B. abortus strain.
Future research in these settings should study the epidemiology of brucellosis in wildlife further, ideally with genetic testing of the bacteria to identify the sources and transmission of Brucella spp. between species, and other vaccination protocols in cattle that result in less serological persistence and therefore interfere less with herd disease categorisation.
|la date de réponse||28 nov. 2018|
|Superviseur||Benoit Muylkens (Président), Xavier De Bolle (Promoteur), Jacques Godfroid (Copromoteur), Tanguy Marcotty (Jury), Claude Saegerman (Jury), David Fretin (Jury) & Richard Kock (Jury)|