Diagnosis and molecular biology of Brucella abortus in Pakistan

Abstract

Brucellosis is a zoonotic disease worldwide and remains a persistent problem in domestic ruminants in Pakistan. It is mainly caused by B. abortus and to some extent by B. melitensis. In humans, it is related to either professionals after accidental exposure or to the general public via consumption of contaminated unpasteurized milk. Brucellosis vaccination is rarely practiced in the ruminants of the country, yet. Although the scientific community is engaged in brucellosis research, animal holders, veterinarians and physicians are not aware of the disease and the zoonotic risk posed by infected animals. A total of 828 bovine (409 buffaloes and 419 cattle), 1,000 small ruminant (500 sheep and 500 goats) and 181 dog sera were collected from organized livestock farms and stray and working dogs in close contact to ruminants from various locations across Punjab, Pakistan, respectively. The sera were subjected to RBPT, iELISA (for B. abortus and B. melitensis) and SAT (for B. canis) and genus- (Brucella) and species-specific (B. abortus and B. melitensis) real-time PCR. In bovines, an overall seroprevalence of 3.9% was found and B. abortus was identified as the etiological agent. In small ruminants, a prevalence of 5.1% was found but the causative bacteria could not be identified, as all investigated sera were negative by real-time PCR. A total of 4.9% of dogs had livestock brucellosis (B. abortus) confirmed by real-time PCR, whereas 37.6% were positive for canine brucellosis (B. canis) using SAT. Risk factors identified for bovines were location and species (buffaloes), for small ruminants location, age (>4years), parity status (>1), breed of the animal and reproductive disorders and for dogs location, age (≥1 years) and a weak body condition (for B. canis infection) and the presence of wounds (for B. abortus infection). These risk factors were significantly associated with brucellosis with higher risk odds. Thus, location and age were the most associated risk factors in all studies. It was shown that brucellosis is a persisting problem at organized livestock farms in Punjab, Pakistan. B. abortus is the disease-causing agent. An alarmingly high prevalence of canine brucellosis caused by B. canis was detected. Robust, cheaper, and more reliable diagnostic tests are needed for both, smooth and rough-LPS Brucella spp., to meet the needs of the local situation. Isolation of the bacteria at any case will be needed for preparation of high-quality DNA for advanced molecular and comparative epidemiological studies. Nevertheless, advanced training, knowledge about the disease dissemination, biosafety and biosecurity measures, awareness programs and implementation of these measures at farms and laboratory levels are obvious needs to combat brucellosis in the future in Pakistan.