Ovine and caprine brucellosis ( Brucella melitensis ).

Abstract

Abstract Brucellosis, caused by Brucella melitensis , remains one of the most common zoonotic diseases worldwide with more than 500 000 human cases reported annually. The bacterial pathogen is classified, by the US Centers for Disease Control (CDC), as a category (B) pathogen and belongs to the World Organisation for Animal Health (OIE) list B diseases. Brucella melitensis , the first species in the genus Brucella to be described, causes abortions in female goats and sheep, unilateral orchitis in males and Malta fever in humans. The natural hosts may be goats and sheep, but the organism is the least species-specific of the brucellae. B. melitensis biovars 1 and 3 are the most frequently isolated in Mediterranean countries. In most circumstances, the primary excretion sources are foetal fluids, vaginal discharges after abortion or full-term parturition, in milk and semen. The epidemiology of human brucellosis has drastically changed over the past decade because of various sanitary, socio-economic and political reasons, together with the evolution of international travel. Besides the public health concern of such an important zoonosis, Brucella infections in animals have an important economic impact especially in developing countries as they cause abortion in pregnant animals, reduce milk production and cause fertility problems. The most reliable and the only unequivocal method for diagnosing animal brucellosis is the isolation of Brucella spp., but polymerase chain reaction (PCR) has the potential to meet the need for better diagnostic tools. It is highly sensitive, very specific, inexpensive and easily adapted to high-volume demands. The process is rapid, simple and requires little manual labour. A sensitive and dependable diagnostic PCR assay for B. melitensis is crucial for controlling the spread of Brucella in animal and human population. Immunological testing for brucellosis among livestock is usually conducted as a component of the disease eradication and surveillance programme rather than as diagnostic support and each country has a different policy for testing livestock. The serological tests commonly used for the diagnosis of B. melitensis infection are the Rose Bengal Test (RBT), Serum Agglutination Test (SAT), Complement Fixation Test (CFT) and enzyme-linked immunosorbent assays (ELISA). The RBT and CFT are the most widely used tests for the serological diagnosis of sheep and goat brucellosis; they are also the official tests for international trade. B. melitensis infection is particularly problematic, because Brucella abortus vaccines do not protect effectively against B. melitensis infection. In regions with a high prevalence of the disease, the only way of controlling and reducing the prevalence of zoonosis is by the vaccination of all susceptible hosts and elimination of infected animals. B. melitensis strain Rev-1, although highly infectious to humans, is considered as the only vaccine available for the control of ovine and caprine brucellosis, especially when administrated at the standard dose by the conjunctival route. However, the Rev-1 vaccine shows a considerable degree of virulence and induces abortions when administered during pregnancy. Also, the antibody response to vaccination cannot be differentiated from the one observed after field infection, which impedes control programmes. Attempts have been made to develop new live attenuated rough B. melitensis vaccines, which are devoid of the O-side chain. Those vaccines await further evaluation in field experiments. The aetiology, isolation, epidemiology, global distributions and new methods of diagnosis and control programmes for ovine and caprine brucellosis have been reviewed in this article.