Brucella canis
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Description and Significance
Brucella canis are gram negative proteobacteria within the Brucellacae family. B. canis is a facultative intracellular pathogen that can survive well outside a host, but prefer to reproduce within the host (“Brucella”). When first found Brucella canis was one of many species of Brucella, but in 1977 it was determined that the only species is Brucella melitensis and the others are just at subtypes of the species. The subtypes only exist for their differences in the animal host it prefers and phenotypic appearance. Brucella canis is one of the subtypes with the preference for dogs as its host. Brucella species was first found by a British doctor named Davis Bruce, hence the name Brucella. In the 19th century in Malta an unknown disease known as Malta fever caused British soldiers to become ill. Bruce determined that the causal agent of the disease was from a bacterium found in milk from infected goats (“Brucella”). The bacterium first gained recognition in the United States as the causal agent of massive abortions that occurred amongst female beagles. The bacterium was then determined to be the causal agent of the infectious disease brucellosis in female and male dogs, which causes abortions and infertility. Dogs may be man’s best friend except for if it is infected by the bacteria, which can cause spread of brucellosis into the human population (“Canine Brucellosis Caused by Brucella Canis”).
Genome
Cell Structure and Metabolism
Brucella canis are small, rough, rod shaped, and non motile gram negative bacteria. Often times it is termed coccobacillai shaped because it looks like short rods rather than long rods. (“Brucellosis” 1999). The significance of the structure of the bacterium is that it has the ability to act as a pathogen, but lacks the structural characteristics that most pathogenic viruses have. B. canis growth is inhibited by a 10% concentration of carbon dioxide (“Brucella”).
Ecology
Brucella canis are found all over the world, but more specifically areas that have poor sanitation and lack good public health safety to support animal infection or lack economic funds to support public health. Some areas where B. canis have been reported are the southern states within the United States, Canada, South America with Mexico included, Central America, Europe, Tunisia, Nigeria, Madagascar, Malaysia, India, Korea, Japan, and China. Australia and New Zealand may be the only areas of the world that do not contain the bacterium (“Canine Brucellosis: Brucella canis”). In Arizona pet diseases are not reported to the department of health making it unknown if the bacterium exists in that area. B. canis can withstand various environmental changes ranged from very high temperatures, lack of sunlight, water, feces, urine, and clothing for several months with out need of an intracellular host (“Brucella canis Q & A for Veterinarians”).
Pathology
Transmission
B. canis can penetrate mucous membranes within the oral cavity and vagina of dogs. The bacterium is found living within the uterine tissue and secretions of female dogs and is shed for months after an abortion. The bacteria found in the semen, testicles, and urine of male dogs and are shed the bacteria for years even past death. B. canis can live within a dog for years before it gets rid of the infection. B. cains is transmitted from dog to dog sexually through vaginal and semen secretions. The bacteria can release from infected dogs by secretions that exit the mouth and nose, and through scars or cuts. Although, dogs are the common host B. canis is zoonotic enabling an infected dogs can cause spread to humans by direct contact with humans usually by just touching an infected dog. The bacterium is mostly exposed to humans that work with the infected animals or the bacterium such as vets and lab workers (Canine Brucellosis: Brucella canis”)
Symptoms
The most common symptoms in female dogs infected by Brucella canis is infertility where abortion occurs during the 45-59 days of pregnancy (“Canine Brucellosis”). Puppies that are born die 2-3 weeks after birth and those that survive carry B. canis in their blood for months (“Canine Brucellosis: Brucella canis”). In males dogs the most common symptom is infertility because of abnormal sperm count, and tesitile atrophy. The most common symptoms in humans are flu like with fever, headache, seating, body aches, and weight loss. It takes 8 days after onset to diagnosis the disease.
Diagnosis
Brucella canis can be diagnosed in an infected dog by using serologic tests and blood cultures. Although useful, serological tests are not the best way to diagnosis B. canis because the antigens they test for cross-react with antibodies of gram negative bacteria that are not pathogenic rather then just the antibodies formed in response to the infection. Blood cultures can be used to confirm a positive serologic test and is more convincing because the presence of B. canis indicates an infection has occurred. The bacterium can be found in the blood of an infected dog 2-4 weeks after infection and survives for 5 or more years (“Brucella canis Q & A for Veterinarians”).
Treatment
Once a dog is infected by Brucella canis it is difficult for the dog to become fully cured. Finding an effective treatment for brucellosis has been very difficult because the bacterium is embedded within the mucous cells of the animal. Antibiotics have been found to have some effect on dogs infected with the bacteria, but only by using many different antibiotics. The problem with antibiotics is that the dog may relapse and the bacteria count is only reduced and not completely removed regardless of the use of the antibiotics. A method of spraying has been used on dogs to reduce spread of the bacterium to others, but unfortunately like the antibiotics it does not remove the bacterium. Long after the bacterium has been successfully treated the dog may still release the bacterium making it difficult for them to try to reproduce after it is claimed to be cured (“Brucella canis Q & A for Veterinarians”). Antibiotics can also be used to cure infected humans and humans respond more quickly to antibiotics (Shin, S., and L. E. Carmichael).
Prevention
All breeding dogs are tested year round to prevent the spread of Brucella canis. Infected dogs are isolated immediately for other dogs and not allowed to breed even after it may be cured.
Current Research
Reference
Centers for Disease Control and Prevention.Brucellosis. 2007. 21, Apr. 2009 <http://www.cdc.gov/ncidod/dbmd/diseaseinfo/Brucellosis_g.htm>
Drs. Foster & Smith, Inc. Brucellosis (Brucella canis) & Abortions in Dogs. 1997. 21 Apr. 2009 <http://www.peteducation.com/article>
Wikimedia Foundation, Inc. Brucella canis. 2009. 21 Apr. 2009 <http://en.wikipedia.org/wiki/Brucella_abortus>