In Ethiopia, brucellosis has been reported from different localities, commonly targeted on bovine, occasionally on sheep and goats, and rarely on camels (31). To the best of knowledge, canine brucellosis had not studied in the country.
This study investigates the seroepidemiology of canine brucellosis in selected areas of East Shoa Zone, Ethiopia. In the study, RBPT containing B. abortus antigen was employed for screening canine brucellosis. However, as RBPT prepared from smooth strains of Brucella cannot detect B. canis infection, a RBPT containing B. canis (rough strain) had used for screening of B. canis infection. Consequently, all dog serum samples were screened twice. Complement fixation test containing B. abortus antigen had been used for confirmation of canine brucellosis due to smooth strains. However, B. canis infection had not serologically confirmed. The present finding revealed that, the overall seroprevalence of canine brucellosis due to smooth strains was 5.4% (CI: 3.35, 7.96) and 4.88% (CI: 2.7, 7.0) using RBPT and CFT, respectively. On the other hand, prevalence of canine brucellosis due to rough strain B. canis was 8.74% (CI: 5.92, 11.56) using RBPTcanis as illustrated in (Table 2).
Detection of canine brucellosis due to smooth strains of Brucella species recorded in the study is almost equal with the report by Cadmus et al. (7) 5.46% (RBPT) in Nigeria; and closely similar with the report by Rahman et al. (31) 4% (RBPT and iELISA) in different parts of Bangladesh. However, lower seroprevalence had reported in Nigeria and China. A seroepidemiological survey done by Xiang et al. (1) from farm dogs, stray dogs and dogs admitted to the Beijing Companion Animal Hospital for immigration and emigration inspection unveiled, 1.42% and 0.42% prevalence of brucellosis due to smooth strains; using RBAT and TAT, respectively. Moreover, no prevalence (0%) had reported by Anyaoha (32) using RBPT and SAT in Enugu and Anambra states of Nigeria. In contrast to the above findings, higher prevalence had reported with prevalence of 32.3% using RBPT and 29.2% using cELISA in Nigeria by Momoh et al. (21), 13.33% using RBPT, 6.67 using SAT, and 10% using ELISA in Bangladesh by Talukder et al. (33).
The result of this study due to the rough strain was in agreement with the report of Öncel et al. (34) in Turkey, who described 7.73% and 7.45% using 2ME-TAT and ELISA, respectively. Whereas, it is higher compared with the studies done by MOSALANEZHAD et al.(35) (4.9%) using Immuno chromatography assay (ICA), in Iran; (36) (0%) using ICA, in Brazil; Ergene et al. (37) (0.99%) using Microplate Aglutination Test in Northen Cyprus; Xiang et al. (30) (3.58%) and (1.33%) using RBAT and TAT, respectively in China; and Cadmus et al. (7) (0,27%) using RSAT, in Nigeria. In contrary, it is lower than the reports of: Chinyoka et al. (12) (17.6%) using ELISA, in Zimbabwe; Behzadi and Mogheiseh (2) (10.62%) using ICA, in Iran; Keid et al.(25) (33.91%) using AGID, in Brazil; and Anyaoha (32) (27.7%) using Solid Phase Immunoassay technique, in Nigeria.
The difference observed could be due to sampling method, sample size of the studies, and sensitivity and specify of serological tests used. It could be also due to the difference in the dog’s rearing culture, awareness of the people, population of stray dogs, dogs keeping purpose, contact with other domestic animals, and health, housing, hygiene, breeding, and feeding management system of the dogs.
In addition to estimating the seroprevalence of canine brucellosis, the association of risk factors had also done. Consequently, no significant association between locations and seroreactivity to both smooth and rough types of Brucella infection had detected by Fisher’s exact test and univariable logistic regression analysis. The final simplified model of multivariable logistic regression analysis however indicated a significant association of dog’s locations with seropositivity of the rough strain of Brucella. As observed in (Table 5), dogs in Batu were 3.86 times more infected with Brucella canis than those in Alage. In contrary, Momoh et al. (21) and Chinyoka et al.(12) Sowed no statistically significant association across study districts. However, it is agreed with the finding of Adedoyin et al. (38) who had also described significant association with the site of samplings.
Unlike Alage and Naka, Batu is urban and the higher prevalence of B. canis infection in Batu might be because of high population of stray dogs in the town. It is known that stray dogs are the museum of many diseases, including brucellois. In Batu, there is a municipal abattoir, many butcher shops and restaurants; thereby many dogs migrate from neighbor villages in search for food; which could increase the number of stray dogs in the town. Perhaps, the big lake (“Lake Zway”) in surrounding of the town which produces thousands of tons of fish each year could also be the reason. This is because upon processing the fish, many fisheries dispose the un-edible offal to the shore of the lake; resulting for assembling freely foraging dogs. Thereupon, many dogs come together and those infected could possibly transmit to others during mating and direct contact. This is supported by studies of Chikweto et al. (3) and Xiang et al. (1), who had demonstrated a higher prevalence of infection in stray dogs compared with non-stray in India and China, respectively.
A significant association of canine brucellosis among different sexes had shown for both smooth and rough types of Brucella infection. A prevalence of 9.39% (in female) and 2.08% (male) was recorded seropositive for anti B. abortus antibodies; likewise, 14.09% in females and 5.42% in males were positive for anti B. canis antibodies. To know the magnitude of the association, the multivariable logistic regression analysis revealed that, male dogs had lower seropositivity to smooth strains by (OR = 0.26, CI; 0.09, 0.79) and to rough strain by (OR = 7.26; CI 2.59–23.32); compared to female dogs shown in (Tables 5 and 6). This result is supported with studies of Talukder et al., Bigdeli et al. and Rahman et al. (31,33,39). Nonetheless, insignificant difference had reported by Mosallanejad et al. (40), Momoh et al. (29), Keid et al. (25), Behzadi and Mogheiseh (41), Xiang et al. (1), Chinyoka et al. (12) and Rhahman et al.,(31) Coitus is one of the principal means of transmission and hence the reason for higher prevalence seen in females might, because of a single infected male be able to mate many females.
Unlike with anti B. canis antibodies, significant association with seropositivity of anti B. abortus antibodies had seen among different age groups. Consequently, 1.25% of those < 2 years old, 4.05% of those between 2 and 4 years old, and 13.58% of those > 4 years were seropositive. The result of multi logistic regression analysis reveals higher odds of the disease (OR = 7.78, CI; 2.59–23.32) in those older than 4 years old compared with those ≤ 2 years old as shown in (Table 5). This is in concordant with many researchers who had reported brucellosis is significantly age dependent and found higher prevalence in adults; like Abubakkar et al. (42), Kebede et al. (43), Osinubi et al. (44), Aulakh et al. (45), and Talukder et al. (33). This might be due to the fact that sexually mature dogs would have higher potential of contracting canine brucellosis through the venereal mode of transmission and the probability of contracting the disease from carrier and other infected animals and materials raises, as time goes.
With respect to maintenance or living condition of the dogs, a very strong statistically significant association with seropositivity of both types of strains of Brucella species was recorded. According to the result of the multi logistic regression, the odd of canine brucellosis due to smooth and rough strains in outdoor dogs were 4.72 and 6.42 times higher compared with indoors, respectively as listed in (Tables 5 and 6). This higher prevalence seen in outdoors might have resulted from the fact that unattended dogs are often in closer contact with infected materials. They had possibilities of getting the infection often in search of their food. Outdoors had a chance of eating infected aborted materials of domestic animals and abattoir wastes when roaming freely; thereafter they could be infected with any of B. abortus, B. melitensis, and B. suis from the materials. Such means of transmission in dogs had explained by Chinyoka et al. (12), Hinic et al. (46), Baek et al. (11), Hensel (47), OIE (20), Cadmus et al. (7), Lucero et al. (48) and Ramamoorthy et al. (49); as well as by the review of Woldemeskel (50). It could also because of the higher probability of such outdoor dogs mating with other infected dogs. Many dogs assemble during breeding season and they would have very close contact with other infected dogs, which is suitable for transmission of the disease by mating. This association of the disease with the living condition of dogs is in consistent with Khairani-Bejo et al. (51) and who got 35% in unattended dogs in Malaysia; and Xieng et al. (2013) from China got low prevalence (0.64%) in indoors but high (28.6%) in stray dogs.
In the present study, obstetrical problems had strongly significantly associated with seropositivity of both anti B. abortus and anti B. canis antibodies. Higher prevalence was found in dogs with history of obstetrical problems (Abortion, infertility, retained fetal membrane, still birth, scrotum dermatitis, swelling of Scrotum, abnormal vaginal discharge) than those hadn’t (Tables 5 and 6). This could be explained by the fact that such reproductive signs are typical outcomes of brucellosis (52–54). As it is described by Holst et al. (55), at the time of abortion the placenta and the discharges can contain up to 1010 colony forming units (cfu) per ml. Thus, 1 ml placental tissue or vaginal discharge is equal to approximately 100,000 infectious doses, and the bitches can have a vaginal discharge for up to 6 weeks after an abortion. Therefore, such dogs will be the source of infection for others. Though insignificant, higher proportion in dogs with history of reproductive problems had reported by Adedoyin et al. (38). They found higher seropositivity in those with history of infertility (OR = 2.62 CI: 1.41–4.84). Besides, Gyuranecz et al. (56) had similarly reported.
The present study concluded that the overall prevalence of canine brucellosis was found high. The disease had significantly associated with living condition of the dogs and outdoor management system was a key risk factor for the occurrence of the disease. Furthermore, respondents had reported abortion cases and the disease had strongly associated with history of reproductive problems. Thence, they can be a source of infection to others. The increasing evidence that B. canis infections are endemic in the dog population also gives rise to the suspicion that, the zoonotic potential may be greater than suspected.