A cross-sectional study of brucellosis was conducted on 261 camels from November 2013 to May 2014 to estimate the seroprevalence and to assess potential risk factors in Fafen zone, Somali regional state, Ethiopia. The study animals were selected using systematic random sampling method. Rose Bengal Plate Test (RBPT) and Complement Fixation Test (CFT) were used as screening tests to detect the presence of Brucella antibodies and to confirm those reactors by RBPT, respectively. Collected data, by all procedures (RBPT and CFT), was carefully entered on to Microsoft Excel spreadsheet and imported to SPSS ver. 20. In the present study, the overall seroprevalence of Brucella in camels in Fafen zone was 1.53%. This level of seroprevalence is enough to be a potential hazard for public health in the study area; therefore, the public especially camel owners and camel milk consumers should be aware of camels as source of brucellosis.
Brucellosis is a worldwide zoonotic disease, recognized as a major cause of heavy economic losses to the livestock industry and a serious human health hazard (Seleem et al., 2010). Five recognized host-adapted species of Gram negative intracellular bacteria, of the genus Brucella,are reported to cause brucellosis (Mantur et al., 2007). The disease can affect almost all domestic species and cross transmission can occur between cattle, sheep, goat, camel and other species (Ghanem et al., 2009). Camels are not known to be primary hosts of Brucella, but they are susceptible to B. abortus, B. melitensis and B. ovis as described by Musa et al., 2008. Camel brucellosis, characterized by abortion, infertility, prolonged calving intervals in females and orchitis in males, is also known for its considerable impact on camel production (Warsame et al.,2012).
In humans, brucellosis can be a serious and debilitating disease with spectrum of non specific multiple symptoms. These symptoms could be due to nephritis, dermatitis, vasculitis, lymphadenopathy, deep vein thrombosis, granulomatous hepatitis, osteomyelitis, or formation of abscesses in internal organs (Gwida et al., 2012). Occasionally, this disease might also lead to death due to the development of endocarditis (Sprague et al., 2012). According to Zewolda and Wereta (2012), the majority of human cases are mainly due to occupational exposure to infected animals or ingestion of unpasteurized dairy products. Moreover, reports like Osoro et al., 2015 suggested a strong association between camel seroprevalence and human seropositivity as compared to other animal species. The seroprevalence of camel brucellosis, from different pastoral and agropastoral areas of Ethiopia, has been reported by Hadush and Pal (2013), Zewolda and Wereta (2012) and Teshome et al., 2003. However, considering the close association of Somali pastoralists with their camels and their habit of consuming raw camel milk, enough work has not been done to determine the seroprevalence and the risk factors of camel brucellosis. Therefore, this study was designed with the objective of estimating the seroprevalence of camel brucellosis in Fafen zone, investigating the associated risk factors for the occurrence of this disease and assessing the awareness level of the Fafen agropastoral community regarding zoonotic brucellosis.
Materials and Methods
Study Area and Animal
Fafen zone, previously known as Jijiga zone, is situated in Somali Regional State, about 630 km East of Addis Ababa. The zone shares border with Shinile zone to the North, the Hararghe highlands of Oromia Region to the West, Dagahabur to the South, and Somalia to the East. Fafen zone is located 9° 20’ N latitude and 45° 56’ E longitude and has an elevation of 1,650 m above sea level (Degefu et al., 2011). The climate is generally semiarid and arid with average annual rainfall ranged from 300 mm to 500 mm and average monthly temperature ranges 16 to 200C (Keskes et al., 2013).
According to the report of Birhan (2013), cattle, sheep, goats and camels are the main productive livestock reared in the area, and camel population was estimated to be 85,000. Camels above six months of age, with no history of vaccination against brucellosis, were selected. Camels above four years were considered matured (at age of puberty), while camels that are 4 and less than 4 years old were considered sexually immature. Herd consisting ≥ 15 and < 15 camels were also considered as large and small herds, respectively.
Questionnaire survey was administered, in the local language (Somaligna), to a total of 32 willing camel owners (17 from Jijiga, 11 from Babile and 4 from Gursum districts), living in selected peasant associations of the three districts. Structured questionnaire formats were developed and used to collect information that focused on the habits of camel product consumption and handling, and aborted fetuses and retained foetal membranes disposal practices. Additionally, age, sex, parity, herd size and abortive history of sampled camels were recorded.
Cross Sectional Survey
A cross-sectional study was conducted on 261 one humped camels in Jijiga, Gursum and Babile districts, of Fafen zone, from November 2013 to May 2014. Jijiga, Babile and Gursum districts were purposively selected based on their accessibility and camel population. Three pastoral associations, from each district, were selected randomly. Camels available for sampling were counted and one camel was randomly selected from every 4-8 camels; no camel was selected if a group contains less than four camels. Sample size was determined according to Thrusfield (2005) for random sampling and calculated using 2.43% expected prevalence (Tilahun et al., 2013), 95% confidence interval and 2% absolute precision. The minimum sample size calculated was 228; however, 261 camels were included in the study for better precision.
Blood Collection and Serological Tests
Blood samples were collected from the jugular vein, using plain vacutainer tubes. The samples were left at room temperature overnight, to allow clotting, for sera separation and separated sera were stored at -20°C until serologically tested. Serological tests, Rose Bengal Plate Test (RBPT) for screening and Complement Fixation Test (CFT) for confirmation, were used to determine the seroprevalence of Brucella. Both tests were conducted following the method described by OIE, (2004), at the National Animal Health Diagnostic and Investigation Center (NAHDIC) in Sebeta, Ethiopia. The results of RBPT were read by examining the degree of agglutination in good light source, and any visible agglutination was considered positive. Sera, reacted positive to RBPT, were retested by CFT to eliminate any cross reaction. Sera with a strong reaction that is more than 75% fixation of the complement (3+) at a dilution of 1:5 and with at least 50% fixation of the complement (2+) at dilutions of 1:10 and 1:20 were classified as positive (+).
The study protocol was peer reviewed and cleared for ethics by the Ethical Review Committee of Jigjiga University, College of Veterinary Medicine. All necessary permits were also obtained from the administration and agricultural office of each districts, and camel owners before commencing blood sample collection.
Data collected by all the procedures (RBPT and CFT) was carefully entered on to Microsoft Excel spreadsheet and imported to SPSS ver. 20. The seroprevalence was calculated by dividing the number of camels found to be seropositive for Brucella, by the total number of camels examined. Chi-square (χ2) test was used to measure the association between the seroprevalence and categorical variables. Fisher’s exact test was used when the outcome variable was too small (below five) to be analyzed by chi square test. Additionally, Odds and likelihood ratio were also used to assess risks factors with two (sex, age, herd size and abortion) and three (district and parity) categorical variables. In all the analyses, confidence level was held at 95% and P < 0.05 was set for statistical significance.
Results of the questionnaire survey showed that 65% (21) of the respondents had no awareness of zoonotic brucellosis. All respondents (100%) consume raw camel milk, at least once in a while, as a traditional treatment for abdominal discomfort. Furthermore, 85% (27) of interviewed pastoralists used their bare hands to handle aborted fetuses and retained foetal membranes.
Overall Prevalence of Camel Brucellosis
From serologically examined 261 camels (101 male and 160 female), 2.3% (6) and 1.53% (4) were seropositive for Brucella antigen by RBPT and CFT, respectively.
Prevalence of Camel Brucellosis by Age and Sex
Higher seroprevalence of brucellosis was observed in female (2.5%) and adult (2.34%) camels than male (0.0%) and young (0.0%) camels, respectively. However, the difference between categories in both groups (sex and age) was not statistically significant (P>0.05) (Table 1).
Table 1: Seroprevalence of Brucella in relation with sex and age
|Group||Camels tested||CFT (%)||OR||95% CI||Fisher’s Exact|
|101||0||1.026||1.001 – 1.051||0.161|
|90||0||1.024||1.0 – 1.048||0.302|
Prevalence of Camel Brucellosis by Abortion and Parity
From 115 adult female camels sampled, 10.43% had history of abortion, 29.6% were none calved, 49.6% had one or two parity while 20.9% had three or more parity. Among 12 camels with the history of abortion and 24 with the history of calving for three or more times, 25% (3) and 8.33% (2) were CFT positive for Brucella, respectively (Table 2 and 3). In addition, there was also statistically significant difference (P<0.05) in seroprevalence of brucellosis, between female camels with and without the history of abortion. However, the difference among three groups of adult female camels, with different calving record, was not statistically significant (P>0.05) (Table 3).
Table 2: Seroprevalence of Brucella in relation with herd size and history of abortion
|Group||Camels Tested||CFT (%)||OR||95% CI||Fisher’s Exact|
|Herd Size ≥15 camels||141||3(2.13)||2.587||0.266 – 25.2||0.627|
|Abortion Yes||12||3(25)||1.32||0.952 – 1.832||0.003|
Prevalence of Camel Brucellosis by Herd Size and District
The seroprevalence of camel brucellosis was also associated with herd size and district (Table 2 and 3). It was higher in larger herds (2.13%) than the small ones (0.83%), and in Jijiga (2.38%) as compared to Babile (0.98%) and Gursum (0.0%) districts. However, the difference among herd sizes and different districts was not statistically significant (P>0.05).
Table 3: Seroprevalence of Brucella in relation with district and parity
|Group||Camels Tested||CFT (%)||Likelihood Ratio||df||P- value|
|1 or 2||57||1(1.75)|
|3 or More than 3||24||2(8.33)|
|Total adult female camels||115||4(3.48)|
The overall seroprevalence of camel brucellosis in this cross-sectional study, 1.53% (4 of 261), is in agreement with the seroprevalence of 0.9% recorded in southeast Ethiopia by Gumi et al., 2013 and 1.8% recorded in Borena by Megersa et al., 2011. However, it was lower than the observation recorded by Hadush et al., 2013, Bekele et al., 2013, Teshome et al., 2003 and Zewolda and Wereta (2012) who reported 4.1%, 5.4%, 5.7% and 7.6%, respectively, in Afar region of Ethiopia and Gameel et al., 1993, who reported 4.1% in Libya. The difference in seroprevalence between the current and previous studies might be due to agro ecological differences of study areas, sample size, animal management and production systems.
The higher seroprevalence of Brucella in female camels (2.5%), recorded in this study, is in agreement with similar previous studies conducted in various parts of Ethiopia by Gumi et al.,2013 and Teshome et al., 2003, and in Kano municipality abattoir, Nigeria by Adamu and Ajogi (1999). On the contrary, Bekele et al., 2013 and Tilahun et al., 2013 reported high seroprevalence of brucellosis in male camels, in Afar and Somali region, respectively. The variation in sex susceptibly for brucellosis could be due to physiological and behavioral differences (Radostits et al., 2000), the relaxation of immunity associated to pregnancy stress or the presence of erythritol in reproductive tract of female camels (Smith et al., 1962). Furthermore, the increase in concentration of erythrtiol and different sex hormones with age and sexual maturity, as described by Radostits et al., 2000, might also explain the higher seroprevalence (2.34%) recorded in adult female camels in this study.
Statistically significant difference in seroprevalence (P<0.05), observed in this study, between female camels with and without the history of abortion, supports the fact that brucellosis is one cause of reproductive problems (Magid et al., 2010. Although herd size is documented by Radostits et al., 2000, as a main factor for transmission of Brucella infection and the result of current study also indicated the difference between large (2.13%) and small (0.83%) herds, it was not statistically significant (P>0.05). Similarly, there was also no statistically significant (P>0.05) difference in seroprevalence of camel brucellosis among the three districts. However, Jijiga district had the highest (2.38%) seroprevalence as compared to Babile (0.98%) and Gursum (0.0%). This could be attributed to the more sedentary and confined life style of the camel owners, which might influence their herd management style, in Jijiga district.
The results of the current study indicated that brucellosis is an established disease in Fafen zone. Animal level risk factor identified for the presence and transmission of the disease were abortion, parity, herd size, sex, age and district. Accordingly, higher seropositivity was recorded in abortive, pluriparous, matured female camels and large herds. The statistical analysis, however, proved abortion as a significant risk factor for transmission of the disease in this study area. Furthermore, considering the close association of pastoralists with their camels and their habit of consuming raw camel milk, this level of seroprevalence can be a potential risk to public health. Therefore, camel rearing pastoralists and individuals working with this species, in this study area, should be educated about the risk of drinking raw camel milk, handling aborted fetuses and retained foetal membranes with their bare hands, the benefits of using anti-brucellosis vaccines to protect the animals. Future efforts should also be done to test camel owners and confirm brucellosis as a public health risk and identify Brucella biotypes of camels in Fafen and other Somali pastoral communities.
Authors would like to thank Sebeta National Animal Health Diagnostic and Investigation Center (NAHDIC), Jigjiga University College of Veterinary Medicine for facilitating the conditions in due course of data collection and sample analysis.