Canine Brucellosis – A New Unknown.
Dr.Shvesh Bandivadekar
Department of Veterinary Pathology,
College of Veterinary Science and AH,
Nanaji Deshmukh Veterinary Science University
Jabalpur (M.P.) – 482001
Email: shvesh@live.com
Brucellosis is a serious bacterial disease among livestock in the world, with a high zoonotic potential to spread among human beings. Although rare, canine brucellosis is an upcoming and emerging disease in dogs, with a potential to not only harm the animal, but also its owner and the veterinarian. This article speaks about the canine counterpart of the livestock disease and its effects on humans.
Introduction:
Brucellosis is caused by Brucella spp. of pathogenic bacteria which is ubiquitous in the world. Livestock is the most common victim of this disease, which results in degradation in reproductive system of the animal, and causes huge economic losses to the farmer. But now – a- days this disease is emerging in a new host. India has a substantial canine population, feral and adopted, and the population is increasing daily with new animals being added to the population and adopted by humans every single day. Thus, canine brucellosis has a strong potential to emerge as a zoonotic disease in the coming future with both, the owners and the veterinarians at a high risk of acquiring the disease.
Etiology:
Canine Brucellosis is commonly caused due to Brucella canis, a gram-negative coccobacilus that is differentiated from the other species of the genus Brucella (except Brucella ovis) in that it forms rugose colonies. It grows in common culture media including triptose agar and does not require CO2 for culture. It affects all breeds of dogs and can occasionally affect human beings. It is most often transmitted through direct dog-to-dog contact via infected body fluids and tissues (e.g. vaginal discharge, aborted fetus, placenta, semen, urine). Other Brucella spp. can also infect dogs (including Brucella abortus and Brucella suis) after dogs consume placenta, aborted fetuses, or uncooked meat from infected livestock or have contact with feral pigs. Once within the dog, the bacterium multiplies and circulates in the blood, moving to and multiplying in body organs. Bacteria can remain within the blood for many years and are easily shed in body fluids. This leads to a high risk of spread to other dogs, especially in dog kennels or dog group environments. Brucellosis is the leading cause of reproductive disease in dogs. Although most infected dogs do not show signs of disease, they are able to infect other dogs. Signs of disease can occur shortly after infection or may not develop for months or years.
Transmission and spread:
Canine brucellosis is most often transmitted through direct contact with infected vaginal discharge, aborted fetus, placenta, semen, or urine. Transmission after oral or nasal contact with an infected dog may also occur. Puppies can be infected in utero if born to an infected dam. In kennels or in high-density dog groups, transmission can occur through contact with contaminated objects (e.g. food or water bowls, bedding). Infected dogs will persistently shed B. canis in fluids for months and likely (intermittently) lifelong. Infection risk is highest for stray and breeding dogs, or those who live in a kennel. Outbreaks are often traced to the introduction of a new infected dog. There is a strong evidence that puppies can get the disease from the infected dam through ingestion of milk, but this is still under debate.
Pathogenesis:
The pathogenesis of canine brucellosis is similar to its livestock counterpart. The routes of entry for the pathogen are genital, oronasal or conjunctivae mucosa. It is also noted that cohabitation with infected males can result in .After Brucella gains entry into the animal, it is phagocytized by macrophages and other phagocytic cells and taken to lymphatic organs (lymph nodes and spleen) and genital organs where they reproduce. Bacteriemia develops 1–4 weeks after infection and persists for at least 6 months and then, intermittently, up to 6 years. Bacteria reach target organs through the blood and produce the pathological changes typical of the disease.
Clinical Signs:
Reproductive disease (e.g. abortion, infertility, fading puppies) is the most common sign of infection. However, spinal and nervous system signs can occur, such as discospondylitis. Some infected dogs never develop clinical disease. General symptoms of brucellosis are not very evident. Pyrexia is rarely present. Loss of shiny coat, general deterioration of condition or intolerance to exercise can be noted in some animals, but these changes are not manifested in most cases. Moreover, symptoms vary according to the organ affected. The most frequent manifestations of infection in the male are severe epididymitis and prostatitis. During the acute stage, the epididymis increases in size and is accompanied by evidence of pain, and the presence of sero-sanguinous fluid in the tunica. Frequent licking of the scrotum produces edema and dermatitis that often becomes contaminated with non-hemolytic staphylococci. The epididymis decreases in size in the chronic phase and becomes hard and the testes often display atrophy. Orchitis is noted infrequently and cases of testicular necrosis with ulcerative scrotal dermatitis, from which B. canis was isolated, have also been reported.
Testicular damage initiates an autoimmune response that produces antisperm antibodies that can be found in blood serum and seminal plasmafrom 11 to 14 weeks post-infection, with the agglutinating activity and titer varying with each other. Auto-agglutination of sperm is often observed from 18 weeks post-infection. These findings suggest that sterility due to canine brucellosis is associated with an autoimmune phenomenon. Generally, the males become sterile. Whether they become sterile or not, they can continue to excrete bacteria in the seminal fluid. Epididymitis generally develops around 5 weeks post-infection and the presence of neutrophils and macrophages in semen and evidence of teratospermia with spermatozoa showing deformed acrosomes, swollen mid-pieces and retained protoplasmic droplets, are also detected at about this stage. Other sperm anomalies, including coiled tails and detatched heads, are observed at 16 weeks post-inoculation and head to head agglutination is detected at 18–27 weeks. Accumulations of inflammatory cells, comprising macrophages with phagocytized sperm, surrounded by masses of neutrophils are seen later. In dogs with bilateral testicular atrophy, azoospermia is a common occurrence. Lymphadenitis, especially involving the retropharyngeal and inguinal nodes, appears in both sexes, although generalized lymphadenitis and follicular hyperplasia of the spleen, are also commonly detected. Examination of aspirates or biopsies of lymphatic ganglions generally reveals lymphatic hyperplasia with a large number of plasmatic cells. B. canis can also produce anterior uveitis and, occasionally, isolated cases of polygranulomatous dermatitis, meningoencephalomyelitis and endocarditis.
Diagnosis:
Usually, diagnosis is made through a combination of clinical signs, PCR and serology tests [e.g. rapid slide agglutination (RSAT, ME-RSAT), agar gel immunodiffusion (AGID)]. False positive tests are common, so confirmatory testing is strongly advised whenever a positive result is obtained. Some tests may not differentiate between B. canis and B. suis. Semen may need to be tested prior to being imported in some regions. It is strongly advised to routinely test all breeding dogs to reduce disease and spread. In many areas, canine brucellosis testing or identification requires reporting to the regional public or animal health agency, due to its zoonotic potential.
Treatment and Prognosis:
Unfortunately, like its livestock counterpart, curative measures against canine brucellosis, rarely work and it’s found that the infection in affected animals persists for life. The animals can be treated with appropriate antibiotics and supportive therapy with a symptomatic approach. Following treatments are known to show some effect on affected animals, but are a subject to discussion based on the availability of drugs and resistance against antibiotics.
1. Oral tetracycline (30 mg/kg) twice daily for 28 days and intravenous streptomycin (20 mg/kg) once daily, for 14 consecutive days at the beginning of the treatment.
2. Oral tetracycline (30 mg/kg) three times a day for 30 days and IM streptomycin 20 mg/kg on days 1–7 and 24–30 of the treatment.
3. Minocycline (10 mg/kg) twice daily, combined with IM streptomycin (4.5 mg/kg) for 7 days
4. Long-acting oxytetracycline (20 mg/kg IM) once a week, for 4 weeks, acompanied by daily injections of streptomycin for the first 7 days.
A treatment with enrofloxacin (20mg/kg IM) for 4 weeks has also found success in treatment.
Prognosis for recovery is very poor, and it is challenging to eradicate disease from affected kennels and breeding colonies.
Management of the outbreaks in kennels:
Since canine brucellosis often goes unnoticed and the bacteria are shed in bodily secretions, the disease can quickly spread throughout a group of dogs (e.g. kennel) if the above testing recommendations are not followed. When multiple dogs have been infected with B. canis in a single location (e.g. kennel), it is strongly recommended to contact someone with experience in veterinary infectious disease risk assessment and outbreak management (i.e. state appointed veterinarian, expert at a nearby veterinary college). Outbreaks are most likely to occur when numerous dogs are housed together, and an infected dog is inadvertently introduced (e.g. breeding program). In such cases, efforts should be aimed at systematically determining which dogs are infected (testing all dogs at least twice 30 days apart) and keeping dogs of different status (e.g. test negative, test positive once, confirmed positive) completely separated. Screening programs will greatly reduce the chance of an outbreak and should be used by every breeder and those introducing high-risk dogs (e.g. stray, national/international rescue) into a dog group.
Zoonotic alert in humans:
People can be infected and become sick with Brucella spp. People are infected with B. canis from contact with an infected dog, its fluids/tissues, or contaminated environment (e.g. bedding, kennel). Disease in people is similar to that in dogs, causing fever and damage to reproductive organs, which can end up as abortions in pregnant women and infertility in men. Disease prevention in people is dependent on quickly identifying infected dogs and taking precautions to avoid contact with the bacteria. These precautions should include washing hands, wearing gloves and dedicated clothing during whelping, and working with a veterinarian to integrate and follow a screening program for all dogs, along with quickly investigating any concerns of reproductive failure. It is of utmost importance to report such outbreaks to the related governmental authorities for appropriate policy application.
