Canine brucellosis

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Abstract

This review discusses the prevalence, etiology, pathogenesis, clinical findings, diagnostic methods, therapy, management and public health considerations of Brucella canis infection in dogs. Canine brucellosis is a contagious infection produced by a gram-negative coccobacilus called Brucella canis. The main sources of infection are vaginal fluids of infected females and urine in males. Routes of entry are venereal, oronasal, conjunctivae mucosa and placenta. The most significant symptoms are late abortions in bitches, epididymitis in males and infertility in both sexes, as well as generalized lymphadenitis, discospondylitis and uveitis. Diagnosis is complex because serology can give false positive results and chronic cases can give negative results, needing to be complemented with bacteriological studies. No antibiotic treatment is 100% effective and the infection often recurs in animals apparently treated successfully. Infected animals must be removed from the kennels and no longer used for breeding. Preferably, males should be castrated and females spayed. Human contagion is not frequent, although it has been reported, and is easily treated.

Introduction

Since Leland Carmichael’s first isolation of Brucella canis in 1966 (Carmichael, 1966), canine brucellosis has been recognized as the cause of great economic loss in kennels. Even today, it is difficult to establish a true diagnosis of this disease and to convince breeders that their animal’s normal reproductive career has ended.

It is especially common in the southern states of the United States (Wooley et al., 1977), Central and South America; surveys of its prevalence have been carried out in Mexico (Flores Castro and Segura, 1976), Brazil (Azevedo et al., 2003), Argentina (Baruta et al., 2001) and Chile (Zamora et al., 1980). In Europe, it has been reported in Germany (Weber and Schliesser, 1977), Spain (Rodriguez Ferri et al., 1982; Mateu de Antonio and Martin Castillo, 1993), Italy (Ciuchini et al., 1982), Czechoslovakia (Sebek et al., 1976), Poland (Pilaszek and Pilaszek, 2000) and from a kennel in France in 1966 (Fontbonne and Garrin-Bastuji, 1966). In Asia, the disease has been reported in India (Srinivasan et al., 1992), Philippines (Baluyut and Duguies, 1997), Korea (Park and Oh, 2001), Japan (Katami et al., 1991), China (Jiang, 1989), Turkey (Diker et al., 1987), Malaysia (Joseph et al., 1983) and Taiwan (Tsai et al., 1983) and in Africa in Nigeria (Adesiyun et al., 1986). A survey of its prevalence was also made in Ontario, Canada (Bosu and Prescott, 1980).

This is a contagious disease with venereal and oral modes of transmission that produces late abortions in females, epididymitis and prostatitis in males. It leads to infertility in both sexes as well as lymphadentitis and diskospondylitis as extragenital symptoms (Carmichael and Kenney, 1968, Carmichael, 1976, Barton, 1977, Johnson and Walker, 1992, Berthelot and Garin Bastuji, 1993, Carmichael, 1999). Diagnosis is difficult because of unstable serum antibody titers that vary from individual to individual as well as between different methods used for their detection. Furthermore, many dogs remain asymptomatic despite being infected, which makes owners unwilling to accept that their dog is ill and should not be used for breeding. Finally, antibiotic treatment has been shown to be efficient in some cases; however, no treatment is 100% effective. In many cases, relapses have occurred after treatment, with the animal appearing “cured” (in terms of bacterial elimination). Consequently, making it is ethically unacceptable to keep a treated animal for breeding purposes. Cases of human infection, mainly of laboratory technicians who have had direct contact with the bacteria and owners of infected animals, have been reported (Swenson et al., 1972, Munford et al., 1975, Godoy et al., 1979, Ramacciotti, 1980, Carmichael and Green, 1990).

Section snippets

Etiology

Despite the description of cases of brucellosis in dogs caused by four of the six species of the genus Brucella, three of these (Brucella melitensis, Brucella suis, Brucella abortus), produce only occasional infections in individual animals, while B. canis is of epidemiological importance. B. canis, isolated for the first time by Leland Carmichael (Carmichael, 1966), is a gram-negative coccobacilus that is differentiated from the other species of the genus brucella (except Brucella ovis) in

Transmission

Contagion is mainly through vaginal secretions, both during estrus and parturition, abortion, and post-partum in the fetus, placenta and lochia, where bacteria can be found in concentrations up to 1010 per ml (Carmichael and Green, 1990). Males excrete bacteria in their semen. Although both sexes excrete bacteria in urine, the concentrations in male urine are higher, reaching 103–106 bacteria/ml of urine (Serikawa et al., 1981, Carmichael and Joubert, 1988). For this reason, urine from a male is

Pathogenesis

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 infection (Serikawa et al., 1981, Carmichael and Joubert, 1988). After Brucella gain entry into the animal, they are 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

Clinical symptoms

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.

Diagnosis

The only method that provides a definitive diagnosis of brucellosis in a dog is the bacteriological isolation of the microorganism. Nevertheless, this is not always possible and an unequivocal diagnosis is not reached in some cases. The different types of serological diagnosis vary in sensitivity and specificity, leading to false positives and negatives, depending upon the stage of the disease and the antigen or the method used for testing. Clinical data and anamnesis must be used in

Treatment

B. canis are intracellular bacteria, which means that antibiotics cannot reach it adequately. In addition, it is sensitive to relatively few antibiotics (Nicoletti and Chase, 1987b). Many different antibiotics have been tried, alone or in combination, and none have been 100% effective in eradicating the disease. Bacteriemia has been eliminated in some cases and negative titers of antibodies, especially of those raised against the bacterial cell wall, have been obtained; however, bacteria remain

Infection control in kennels

When abortions, infertility or epididymitis are detected in dogs during a routine inspection of dog kennels, it is necessary to carry out an immediate serological test for Brucella on the affected animals. If positive, the following steps are recommended:

  • 1.

    Quarantine the establishment during the period of eradication of the disease. If dogs previously from the same kennel are brought back to the kennel, they can re-infect the kennel.

  • 2.

    Carry out serological tests and blood cultures on all the

Prevention

All females must be routinely tested serologically before mating. All males should be subjected to similar testing before mating. Males and females should be subjected to at least one test per semester to minimize the risk of infection. All new animals (male or female) that enter the kennel should be examined and should be quarantined for 8–12 weeks. No animals exposed to the infectious agent, or those displaying symptoms similar to those of brucellosis, should be bought.

Public health significance

The incidence of the illness in human beings is not exactly known. Although B. canis affects man, there are few cases reported and the illness, generally from close contact with material from abortions or secretions during estrus, is often mild (Shin and Carmichael, 1999). There have been cases of infection in laboratories directly involved in work with the bacteria (Godoy et al, 1979). The illness starts with prolonged fever, enlarged lymph glands (Shin and Carmichael, 1999), pharyngitis (

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