Innocuity and immune response to <i>Brucella melitensis</i> Rev.1 vaccine in camels (<i>Camelus dromedarius</i>)

Abstract

A field trial was conducted in a camel brucellosis-free herd to evaluate antibody response to the Brucella melitensis Rev.1 vaccine in camels and assess shedding of the vaccine strain in milk. Twenty eight camels were divided into four groups according to their age and vaccination route. Groups A (n=3) and B (n=3) consisted of non-pregnant lactating female camels, vaccinated through subcutaneous and conjunctival routes, respectively. Groups C (n=10) consisted of 8-11 months old calves vaccinated through conjunctival route. The rest of the herd (n=12) composed of female and young camels were not vaccinated and were considered as the control group. Each animal from groups A, B and C was given the recommended dose of 2 x 10⁹ colony forming units of Rev.1 vaccine irrespective of age or route of vaccination. Blood samples were collected from all the animals at the time of vaccination and at weekly, bi-weekly and monthly interval until 32 weeks post vaccination and from controls at weeks 8 and 24. The serological tests used were modified Rose Bengal Test, sero agglutination test, and an indirect Enzyme Linked Immunosorbent Assay. Milk samples were collected from all vaccinated female camels and tested for the presence of Rev.1 vaccine strain. Most vaccinated animals started to show an antibody response at week 2 and remained positive until week 16. By week 20 post-vaccination all animals in the three groups were tested negative for Brucella antibodies. Bacteriological analysis of milk samples did not allow any isolation of Brucella melitensis. All samples were found Brucella negative in PCR analysis. The results of this study indicate that the Rev.1 vaccine induces seroconversion in camels. Rev.1 vaccine strain is not excreted in the milk of camels. These findings are promising as to the safe use of the Rev.1 vaccine in camels.

Keywords: Brucella melitensis, Camel, Milk, Rev.1 vaccine