Canine Brucellosis

Description

Canine brucellosis is caused by the intracellular gram negative bacteria B. canis. The disease predominantly affects the reproductive system causing abortion and infertility in females and epididymitis and infertility in males. Other systems can also be affected, causing uveitis, discospondylitis, dermatitis and osteomyelitis. Transmission to humans has been documented but is very rare.

Animals are infected when the organism gains entry to the body at mucus membranes: vaginal, oral and conjunctival. Macrophages then phagocytose B. canis which targets lymphoid and genital tissue. A transient lymphoid hyperplasia and hyperglobinemia develop in the early stages of infection followed by a bacteraemia 1-4 weeks post initial infection which can persist for up to 5 years. Brucellosis is transmitted by females at oestrus, breeding, post abortion, transplacenta and is shed in urine, faeces and milk. Males shed the organism in semen for up to 2 years and in urine for up to 3 months. A cell mediated immune response is needed to clear the organism; however non-protective antibody may develop which complicates diagnosis and treatment of the disease.

Signalment

The prevalence of brucellosis is relatively low (1-8% in the U.S); areas affected include the U.S, Japan, South America, Spain, Tunisia and Germany. The disease is more common in stray animals and breeding kennels. There is no breed susceptibility reported but beagles are over represented in cases in the U.S. The disease usually affects sexually mature animals and females more than males.

Diagnosis

Clinical Signs

Female:

• Abortion
• Post abortion vaginal discharge
• Early embryonic loss

The usual clinical presentation is of abortion in late gestation of an otherwise healthy bitch which is non-pyrexic. Infertility, early embryonic loss and small litters are also reported; if a pregnancy continues to term the puppies die in the neonatal period.

Male:

• Scrotal enlargement
• Epididymitis
• Seminal abnormalities
• Testicular atrophy
• Infertility

Laboratory Tests

The organism can be cultured from aborted tissue or vaginal discharge following abortion, these tissues contain high concentrations of B. canis and if these are not available then culture can be attempted on blood, urine or semen but is more difficult. Culture is difficult because B. canis is slow growing and contamination with other bacteria will result in faster growing bacteria over growing B. canis.

Early infection can be detected by haemoculture as a bacteremia is high from 4 weeks to 6 months after which it declines.

The organism can be identified using Slide agglutination, ELISA, agar gel immunodiffusion and PCR.

Treatment

Treatment with antibiotics is rarely effective and animals which have apparently recovered from the disease can act as carriers and infection can recur. The organism is difficult to target due to its intracellular status.

In cases occurring in breeding kennels infected animals should be euthanased and all other animals should be tested monthly and also eliminated if found to be positive. Testing should continue until all animals have tested negative for three consecutive months.

In individual pet cases where euthanasia is unacceptable to the owner then treatment with antibiotics such as Tetracyclines, doxycline and gentamycin can be attempted. The animal must also be neutered and isolated from other animals for the duration of treatment.

No vaccine exists.

Prognosis

The prognosis is poor, infected animals should be euthanased to prevent spread of infection. Treatment with antibiotics is rarely successful.

References

• Merck & Co (2008) The Merck Veterinary Manual (Eighth Edition) Merial
• Nelson, R.W. and Couto, C.G. (2009) Small Animal Internal Medicine (Fourth Edition) Mosby Elsevier
• Tilley, L.P. and Smith, F.W.K.(2004)The 5-minute Veterinary Consult (Third edition) Lippincott, Williams & Wilkins