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.
