Abstract
Brucellosis is of worldwide economic and public health importance. Heifer vaccination with live attenuated Brucella abortus strain 19 (S19) is the cornerstone of control in low- and middle-income countries. Antibody persistence induced by S19 is directly correlated with the number of colony-forming units (CFU) per dose. There are two vaccination methods: a ‘high’ dose (5–8 × 1010 CFU) subcutaneously injected or one or two ‘low’ doses (5 × 109 CFU) through the conjunctival route. This study aimed to evaluate serological reactions to the ‘high’ dose and possible implications of the serological findings on disease control. This study included 58 female cases, vaccinated at Day 0, and 29 male controls. Serum was drawn repeatedly and tested for Brucella antibodies using the Rose Bengal Test (RBT) and an indirect enzyme-linked immunosorbent assay (iELISA). The cases showed a rapid antibody response with peak RBT positivity (98%) at 2 weeks and iELISA (95%) at 8 weeks, then decreased in an inverse logistic curve to 14% RBT and 32% iELISA positive at 59 weeks and at 4.5 years 57% (4/7 cases) demonstrated a persistent immune response (RBT, iELISA or Brucellin skin test) to Brucella spp. Our study is the first of its kind documenting the persistence of antibodies in an African communal farming setting for over a year to years after ‘high’ dose S19 vaccination, which can be difficult to differentiate from a response to infection with wild-type B. abortus. A recommendation could be using a ‘low’ dose or different route of vaccination.
Highlights
Brucellosis caused by Brucella abortus is a widely-distributed zoonosis of importance to public health (Corbel 2006)
The Rose Bengal Test (RBT) is seen as the best screening test for brucellosis in this context (Godfroid, Nielsen & Saegerman 2010) and indirect enzyme-linked immunosorbent assay (iELISA) is seen as a confirmatory test as it is more specific than the RBT (Corbel 2006), both of which are recommended by the Organisation for Animal Health (OIE)
This study revealed a comprehensive and rapid antibody response in heifers vaccinated with strain 19 (S19) vaccine in this communal farming setting
Summary
Brucellosis caused by Brucella abortus is a widely-distributed zoonosis of importance to public health (Corbel 2006). The KwaZulu-Natal province in South Africa, with a setting similar to the study site, had an estimated prevalence of 0% – 1.5% (Hesterberg et al 2008). Detection of disease is done using the Rose Bengal Test (RBT) as the serological screening test and the complement fixation test (CFT) as the confirmatory test. Both tests can give false-positive reactions owing to strain 19 (S19) vaccination (World Organisation for Animal Health 2009). Vaccination of heifers together with brucellosis testing and slaughter of positive animals is the foundation for control of brucellosis in cattle in endemic areas (Nicoletti 2010). In resourcelimited settings, slaughter of positive reactors is often not possible because of financial limitations (Moriyón et al 2004)
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