The term “brucellosis” refers to a disease that results from infection of humans and animals with Brucella spp. Although there are much more genetic variations among strains of Escherichia coli or serotypes of Salmonella enterica than among Brucella species , Brucella spp. are usually host restricted, which has been the traditional approach for naming the species. For example, among classical Brucella spp., namely B. melitensis, B. suis, B. abortus, B. canis, B. ovis , and B. neotomae have small ruminants, pigs, cattle, dogs, sheep, and rodents as their preferred hosts, respectively . During the past recent years, the genus underwent a marked expansion with the recognition of additional species, including: B. ceti , B. pinnipedialis , B. microti , B. inopinata , B. papionis , and B. vulpis , which have cetaceans (e.g., whales and dolphins), seals, common vole (Microtus arvalis), undetermined host, baboons, and wolves as preferential hosts, respectively. Brucellosis is one of the most important zoonotic diseases worldwide , and most of Brucella ABBOTT species are capable of infecting humans, although they have a highly variable zoonotic potential.
B. melitensis is the most pathogenic species of Brucella for humans,
with the exposure to only 1–10 CFU (colony forming units) being sufficient for establishment of infection, whereas B. suis and B. abortus have intermediate zoonotic potential. B. canis has the lowest zoonotic potential among the classic Brucella spp., and there are no documented cases of human infection with B. ovis
- The pathobiology of brucellosis in livestock species have been extensively studied, particularly due to its zoonotic and public health significance as well as due to highly significant economic losses for the animal industry . In contrast, studies on canine brucellosis are mostly based on fragmented seroepidemiologic surveys .
- Importantly, canine infections with B. canis are widespread, which considering the limitations for accurate diagnosis in dogs and human patients , it certainly makes human brucellosis associated with B. canis a markedly neglected zoonotic disease. Therefore, the goal of this review was to provide an updated overview of the literature regarding different aspects B. canis infection in dogs as well as its relevance as a zoonotic disease, considering perspectives for improving the control of this disease.
Epidemiology of Canine Brucellosis
B. canis is the most common cause of canine brucellosis, although occasional infections with B. melitensis, B. abortus, or B. suis occur in dogs that have close contact with tissues or secretions of infected livestock animals, especially raw milk, aborted fetuses, and placentas . Interestingly, B. canis was isolated from a lymph node of a cow, but the clinical and epidemiological implications of this finding is unknown .
In dogs, there is no evidence of breed predisposition, and the high number of well-documented outbreaks in beagles may be due to the broad use of this breed for research purposes . B. canis infection in dogs has been reported during outbreaks in kennels or serological surveys of stray and pet dogs. Serologic surveys demonstrated higher frequencies of B. canis infections in stray dogs when compared to responsibly owned dogs , probably due to the absence of mating control in stray dogs, which favors transmission of the disease. In a recent study performed in Mississippi, the prevalence of B. canis infection in shelter dogs was 2.3%, but the prevalence in shelters varies from 0 to 8.6%, which indicates that a small number of shelters may have a high seroprevalence of brucellosis .
B. canis was first isolated in 1966 from aborted fetuses in a Beagle kennel in the USA during an outbreak of abortions and reproductive failures . Since then, canine brucellosis caused by B. canis has been diagnosed in several countries , with the exception of Antarctica .
Although the literature supports the notion that B. canis infection has a worldwide distribution , there are no consistent epidemiological studies assessing the prevalence of canine brucellosis. The lack of specific and efficient commercial laboratory tests may contribute to neglect the importance of canine brucellosis in many countries .
Canine brucellosis is an infectious and zoonotic disease caused by Brucella canis, which has been reported worldwide, and is a major public health concern due to close contact between dogs and humans.
In dogs, canine brucellosis manifests with abortion outbreaks, reproductive failure, enlargement of lymph nodes, and occasionally affects the osteoarticular system, although the occurrence of asymptomatic infections in dogs are not uncommon. In humans, the disease is associated with a febrile syndrome, commonly with non-specific symptoms including splenomegaly, fatigue, and weakness.
Infection of dogs occurs mostly by the oronasal route when in contact with contaminated tissues such as aborted fetuses, semen, urine, and vaginal secretions. In humans, contact with contaminated fluids from infected dogs is an important source of infection, and it is an occupational risk for veterinarians, breeders, laboratory workers, among other professionals who deal with infected animals or biological samples. The diagnosis in dogs is largely based on serologic methods. However, serologic diagnosis of canine brucellosis remains very challenging due to the low accuracy of available tests. Molecular diagnostic methods have been increasingly used in the past few years. Treatment of infected dogs is associated with a high frequency of relapse, and should be employed only in selected cases.
Currently there are no commercially available vaccines for prevention of canine brucellosis. Therefore, development of novel and improved diagnostic methods as well as the development of efficacious and safe vaccination protocols are needed for an effective control of canine brucellosis and its associated zoonotic risk.