Serological Survey of Canine Brucella Infection within the North-Central Nigeria

INTRODUCTION

The dog population in Nigeria is put at about 16.7 million according to the dog population census report by the Management Information System of the Federal Department of Livestock and Pest Control (MIS, 2002). Food and Agricultural Organisation (FAO) (2006) reported that about 90% of these dogs roam freely and are prone to a number of infectious and non-infectious diseases, as these animals are generally in parts of the world where human and animal health services are scarcely provided or non-existent.^[1]

One common infectious disease that is a major cause of production losses in terms of abortion, infertility, low conception rates, stillbirth, and low survival rate of neonates in dog is brucellosis. Brucellosis is in fact a silent threat to canine breeding management and dog population worldwide, except New Zealand and Australia (Carmichael and Shin, 2004).^[2]

Canine brucellosis, also known as infectious abortion of dogs, is a reproductive disease of canids caused by Gram-negative cocobacillary bacterium of the genus Brucella (Hensel et al., 2018).^[3] Brucella canis is the species found primarily in dogs. It is a common zoonotic disease of domesticated and wild canidae with other animals and humans (especially where exposure is occupationally) by direct contact with infected animals, ingestion of contaminated food particles, or through aerosol inhalation (Weir et al., 2023).^[4]

A large-scale and planned study to determine the status of canine brucellosis in Zaria, Kaduna State, and Nigeria as a whole has not been carried out. The success of any control program of canine brucellosis can only be achieved if there is information on the disease which could only be generated through the conduct of a survey.

MATERIAL AND METHODS

Study area

A structured questionnaire and survey of dogs in residential areas, breeding sites and outskirts with guard dogs for a year and half was conducted with a view to determine the epidemiology of Canine brucellosis among dogs in Zaria and its environs, located in the Northern Guinea Savannah zone of Nigeria, on latitude, 11°5’ 8” N and longitude, 7°43’ 12” E and at an elevation of 650 m above sea level. It has an average annual maximum and minimum ambient temperature of 31.0 ± 3.2°C and 18.0 ± 37°C, respectively. Zaria has an average annual rainfall of 1100 mm, usually lasting from May to October, and with a mean relative humidity of 72%. The dry season covers the period from November to April with mean daily temperatures ranging from 15°C to 36°C, and mean relative humidity of between 20% and 37% (Igono et al., 1982) [Figure 1].^[5]

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Figure 1:

Map showing the study area (Zaria and its environs).

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Rose Bengal plate test

Briefly, equal volumes (30 uL) of antigen and test serum were mixed thoroughly on a plate using a stick applicator, and the plate was rocked for 4 minutes. The appearance or absence of agglutination (rough or smooth clumps with rim edges) was scored positive (+) and negative (−), respectively [Figure 2]. Figure 3 show the various assay types, this may be expunged as I cannot seem to place the full forms of LCL or UCL. It has to do with the container load, less than container load but not too sure.

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Figure 2:

Brucellosis test using Rose Bengal Plate test.

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Figure 3:

Computer display of the various assay type available in the laboratory Multiskan EXAQ microplate reader system. EX: Excellence, LCL: Lower control unit, UCL: Upper control unit.

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cELISA

The cELISA kit was supplied by the IAEA Animal Production and Health Section Laboratory Unit, Vienna, Austria. The kit contained cELISA plate and reagents. The plate was coated with lipopolysaccharide of B. canis M16. The reagents included control sera, diluting buffer, conjugate, and washing solution. The reagents were reconstituted in line with the instruction on the label. Positive samples had a brilliantly shining light greenish appearance, whereas negative samples appeared orange in color. The optical density (OD) was measured at 450 nm using a microplate ELISA reader (microplate reader multiskan, Fisher Scientific OY- Ratastie 2, 01620 Vantaa - Finland. Thermo Fisher Scientific Inc.). A positive/negative cutoff was calculated as 60% (as instructed by the manufacturer) of the mean of the OD of the conjugate control wells. Samples in wells with OD equal to or less than the cut-off point were scored positive, while those above were negative. This is shown in Figures 3 and 4.

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Figure 4:

Optical density reading for the various test samples for one of the competitive enzyme linked immunosorbent assay test.

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RESULTS

As shown in Table 1 above, detections of canine brucellosis with the two serological tests, in which different levels of result were obtained. However, cELISA yielded the better result, which was the highest rate (31.4%) for the survey, than those of the other test methods, the RBPT which has a lower rate (14.65%). All samples positive for RBPT were also positive for the cELISA. All samples positive for RBPT were also positive for the cELISA. The Sex distribution of reproductive diseases of dogs and the prevalence of specific reproductive diseases in each sex is shown in Table 2 where it showed that the female dogs were most affected. Tables 3-5 show the sex, age and breed distributions of positive cases of brucellosis among dogs in Zaria respectively.

DISCUSSION

The prevalence of brucellosis recorded in this survey (31.4%) indicates that brucellosis infection in dog is of common occurrence in the study area. The prevalence could be attributed to be lack of lack of regulatory measures in controlling animal diseases generally in Nigeria (Cadmus et al. 2004),^[10] uncontrolled movement, and free roam nature of livestock within and across the regions, even trans borders to neighboring countries (Ogundipe, 2001),^[11] ignorance of the mode of transmission of the disease among the populace (Adesokan et al., 2013),^[12] keeping the affected animals within a herd or households (Mai et al., 2012),^[13] and many other factor. Brucellosis among dog population in the households or within herds of other animals, such as cattle and small ruminants, had not been elaborately studied in Nigeria. Literature only revealed previous studies that documented the rate of reported cases of the disease of Brucella infections brought to the clinic compared to the total cases of all diseases over the duration of time, for example, Adesiyun et al. (2003)^[14] had reported a prevalence rate of 14.6% in three local governments in Kaduna State, part of this study area. Furthermore, Osinubi et al. (2004)^[15] reported a 26.7% prevalence rate of the disease as studied from the cases brought to the Small Animal Clinic of Ahmadu Bello University, Zaria, over a 10-year period.

The prevalence recorded with the RBPT (14.7%) is lower than recorded with cELISA (31.4%). This finding also agrees with that of Osinubi et al. (2004)^[15] who recorded higher prevalence with cELISA than the RBPT. This can be explained by the fact that serological tests differ in their ability to detect a particular immunoglobulin isotopes found in the blood in early or acute infections are the immunoglobulin (Ig)M and IgG1 (Ismail et al., 2002)^[16] which may not be seen in cases with insidious onset, in chronic, recurrent, and relapse cases, where IgG2, IgG3, and IgA are predominant (Diaz et al., 2011).^[17] While the RBPT is better suited for detecting acute cases (Chienais et al., 2012),^[18] i.e., IgM and IgG1M, the cELISA is the test of choice in chronic cases (Smits et al., 2003).^[19] This may therefore suggest that most of the cases in this study were of the chronic form of brucellosis, which is supported by a previous report that many cases of brucellosis in endemic areas could be in chronic or relapse stage of the disease (Serra and Vinas, 2004).^[20] The IgG ELISA has been used to monitor chronic and relapse infections because of its better ability to detect IgG and IgA in sera (Smits et al., 2003).^[19]

Although the study found no association between prevalence of brucellosis and sex, higher sero-positivity was recorded among the females than males. The result is in agreement with other studies (Adesiyun et al., 1986: Osinubi et al., 2004)^[15,21] that found the prevalence of brucellosis to be higher in female than the male dogs.

Sex and breed do not appear to be important epidemiological factors in canine brucellosis. A portentous substance (erythrithol) which is a growth supporting factor for Brucella organisms is reported to be present in higher concentration in the placenta and the endometrium of female dogs than in the seminal vesicles and testes of the males (Keppie et al., 1965)^[22] accounting for why the organism has a predilection mostly for these tissues in females than those of the males, this could possibly explain the observed higher infection rates in the females than in the male, though not statistically significant.

The need for this serological survey of canine brucellosis was in view of incessant reports of abortion and infertility cases that were commonly presented to the various veterinary clinics from these areas vis-à-vis the public health and economic implications. The significance attached to the households and resident herds visited was informed by the zoonotic nature of the disease. Furthermore, the disease causes abortion and stillbirth in bitches, orchitis, and hygroma in male dogs and these constitute huge economic losses. The high prevalence in these areas could stem from the fact that these dogs that scavenge and roam around the neighborhood mixed together with other dogs, shared niches, food, and drinking water from stagnant sources which may have been contaminated by the infected dogs or other animals from the same area on free roam or from particulate objects. The epidemiological importance of the survey in this study area is to ensure good husbandry practices, improved farm management systems like proper sanitations, good feeding biosecurity measures as control strategies against diseases. Brucella infection as a silent threat may be going unnoticed in the dog population in the area; this should not be ignored in view of the public health importance of the disease. Therefore, holistic steps to de-escalate the menace by way of screening dogs and other animals for culling the affected ones, disinfecting and re-stocking with dogs and other animals free from the disease such are instituted. Free roaming dogs and water sources point should be controlled to eradicate Brucella infection and other infections inimical to breeding and welfare of dogs and human population.

CONCLUSION

The study showed that brucellosis is prevalent among dogs in the study area which is endemic. There is the need to test individuals in regular contact with the dogs for brucellosis. Food products derived from these animals should be properly cooked to protect the consumers from Brucella infection. In addition, individuals in regular contact with bitches having reproductive related cases and genitalia diseases should be mindful of personal protection, especially when living with members of their families in the surrounding of these animals. Furthermore, households and herd owners as well as members of the public who consume unpasteurized milk and other products of these in contact animals of these dogs should be educated on the economic and public health importance of the disease.