A cross sectional study on the seroprevalence of bovine brucellosis in Al-Najaf province in Iraq

Khaleel Z. Al-Alo and Ahmed Jassim Mohammed

Department of Veterinary Clinical Sciences, College of Veterinary Medicine, University of Kufa, Kufa, Iraq

khaleelz.khaleel@uokufa.edu.iq, 0000-0002-6681-0132

ahmedj.almialy@uokufa.edu.iq, 0000-0002-9782-0448

2020-05-19

2021-05-04

Abstract

Brucellosis is an endemic disease in many countries of the middle east including Iraq, despite the high attempts to control the disease in animals using vaccination programs. The study was conducted from January - March 2012, to determine the prevalence of bovine brucellosis in the Al-Najaf province in Iraq, which represent risk factors associated with brucellosis in cattle. Blood samples were collected from 172 cows and 15 bulls of 20 dual-purpose cattle herds. Serological examinations are the most useful and widely used tool for the diagnosis of brucellosis in man and animals. All animal serum samples were tested by the Rose Bengal plate test (RBT), and the positive cases were confirmed by competitive enzyme-linked immunosorbent assay (c-ELISA). The overall prevalence of brucellosis was 5.81% divided between 5.81% in females and 0% in males, and 40% as herd numbers level. Females showed a higher seropositive reaction to the disease than males. In conclusion, this study demonstrated the presence of the disease and detected the seropositive reactions in animal samples in different farms of the province, with a difference in infection rate regarding the risk factor. Sanitary measures must be taken to avoid the occurrence and spread of the disease in humans and animals.

Keywords: Brucellosis, Cattle, Rose Bengal, c-ELISA, Al-Najaf, Iraq

دراسة مقطعیة-عرضیة مسحیة للانتشار المصلی لمرض الإجهاض الساری البقری فی محافظة النجف فی العراق

خلیل زینل خلیل العلو و احمد جاسم محمد

فرع العلوم السریریة، کلیة الطب البیطری، جامعة الکوفة، الکوفة، العراق

الخلاصة

مرض الإجهاض الساری هو مرض مستوطن فی العدید من دول الشرق الأوسط بما فی ذلک العراق، على الرغم من المحاولات العدیدة للسیطرة علیه فی الحیوانات عن طریق برامج التلقیح. أجریت الدراسة لتحدید مدى انتشار مرض الاجهاض الساری فی الابقار فی محافظة النجف فی العراق لأن هذا الانتشار الواسع یشکل أحد عوامل الخطورة التی تؤثر على الصحة العامة فی المجتمع. تم جمع عینات الدم من 172 بقرة و15 ثور من 20 مزرعة ماشیة تربى لغرض اللحوم والحلیب للفترة من شهر کانون الثانی الى اذار عام 2012. الفحوصات المصلیة هی الأداة الأکثر استخدامًا لتشخیص مرض الاجهاض الساری فی الإنسان والحیوان. تم استخدام اختبار لوحة الروز بنغال وتأکید الحالات الإیجابیة بواسطة اختبار الالیزا المناعی التنافسی. بلغ معدل الانتشار الکلی لمرض الإجهاض الساری 5.81٪ وکان بنسبة 5.81٪ عند الإناث، و 0٪ عند الذکور، و 40٪ کمستوى أعداد القطعان. أظهرت الإناث استجابة مناعیة مصلیة للمرض أکثر من الذکور. اکدت هذه الدراسة وجود المرض وتم تشخیص الاستجابة المناعیة المصلیة الموجبة فی عینات الحیوانات فی المزارع المختلفة فی محافظة النجف-العراق، مع اختلاف فی معدل الإصابة فیما یتعلق بجنس الحیوان. یجب اتخاذ التدابیر الصحیة لتجنب حدوث وانتشار المرض فی الإنسان والحیوان.

Introduction

Brucellosis is a bacterial infectious disease caused by the gram-negative Brucella species, that can affect domestic, wild animals as well as humans (1). Brucellosis can cause considerable economic losses in livestock production which have been estimated at 7-12 million dollars per each year (2). In Iraq, several studies have been carried out on brucellosis seroprevalence (3). In Mosul city, seroprevalence rate was 18.25% and 5.8% in cattle (4), and 8.50 % in buffalo (5). In the camel, the prevalence rate was 16.29% in Wasit Province (6), and 8.6% in Arbil Province (7). In Mosul province, the infection rate of ovine brucellosis was 15.9 % using the ELISA test on different samples of sheep herds (8) and 25.6% using Rose Bengal test and 2- mercaptoethanol test in goats (9). In cattle, abortion is presented as the main clinical manifestation of the disease with B. abortus strain (10). Potential predisposing and risk factors include the climatic conditions, geographical region, animal species, sex, age, compliance with sanitary measures, such as milk and dairy products pasteurization, disposal of an aborted fetus (11). In Mosul city, Al-Iraqi reported a seroprevalence of Brucella antibodies in female buffalo 50.8% and 28.8% by using C-ELISA and RBT respectively (5). Another study showed that the seroprevalence of Brucella antibodies in cattle was 16.7% and 18.3% by using C-ELISA and RBT respectively (12).

The objective of this study was to determine the prevalence of bovine brucellosis in Al-Najaf province in Iraq.

Materials and methods

Study area and population

The seroprevalence of Brucellosis was performed in clinically healthy 198 animals 172 cows, 15 bulls aged more than 36 months, on 20 dual purpose cattle herds in Al-Najaf province during the period January - March 2012 was used in this study. The number of examined animals represents 1.01% of the cattle population in the province.

Sample collection and study design

Blood samples were collected from the coccygeal vein of 198 (172 cow, 15 bulls) clinically healthy animals. Serum was separated by centrifugation of blood sample at 2000 rpm/5m and kept at -20ºC. All samples were labeled with sampling date, animal age, and sex.

Serological test

Antibodies against Brucella spp. were detected by the Rose Bengal test using a commercially available test kit (RBT; VIRCELL, Granada, Spain). Competitive ELISA test was used to confirm the positive results of Rose Bengal (Synbiotics®) (13). The kits were used as directed by the manufacturer and all tests were performed by using (Bio-Tek Instruments, Inc. ELX-800). The dye of Rose Bengal is buffered at PH 3.65 ± 0.05, because the low pH reduces the nonspecific agglutination of smooth Brucella antigens and favors the activity of antibodies especially the IgG1 isotype.

Statistical analysis

Data obtained from the study were expressed as mean ± standard error of the mean (mean ± SEM) and analyzed using the SPSS software package (Version 16). One-way ANOVA was used to compare the differences in the mean values between the male and female animals. Values of P < 0.05 were considered significant.

Results

The results showed that the overall prevalence in cattle would be 5.05%, and the prevalence rate of the disease in screened bulls and cows was 0.0 and 5.81% respectively (Table 1). Our study showed that the positive cases of brucellosis were found to be present in eight herds from a total of twenty herds on the basis of Rose Bengal test and cELISA test, in which the general prevalence rate was 40%.

Table 1: Seroprevalence rate of bovine brucellosis in cattle older than 36 months in Al-Najaf province

Discussion

The results of the current study agree with the results of different studies of bovine brucellosis seroprevalence. The different condition of animal’s husbandry included environmental factors, husbandry system, and management practices reveal the different percentage of infection with the disease (14). There is a great difference in the infection rate of the disease in various Iraqi cities, and this runs in the same direction with the results gained by other researchers in the world. It is mentioned that the disease prevalence differs markedly between countries and within the one country; this great difference belongs to many factors such as occupational, socioeconomic, and demographic factors. In the same city there are also changes in the rate of seroprevalence in animals in various areas (15).

In the studied area in Al-Najaf, the main factor for the prevalence rate is the contamination with uterine discharge, vaginal discharge, milk, aborted fetus, and semen of infected bulls. Feces of infected animals also considered as source of infection. According to the sex of the animal, the prevalence rate of the disease in this study was 0% in males and 5.81% in females. There are significant differences between males and females in susceptibility towards the disease. Anyway, there are different data regarding the disease prevalence in both animal sexes, and our results are consistent with the results of previous researchers, who recorded that the females are more susceptible to infection than males, whereas some scientists found that there is no apparent relation between sex of animal and susceptibility to Brucella infection (6). Other researchers suspected that ruminant’s males are more affected by brucellosis than females (16).

As reported by different organizations such as OIE, FAO, and WHO, brucellosis is seemed to be one of the significant zoonotic in the world through ingesting of unpasteurized milk or dairy products of diseased animals (10). Al-Hamdani and Al-Zawadi (17) mentioned that there is no difference between RBT, tube agglutination test, and 2-mercaptoethanol, while other studies mentioned that the tube agglutination, rose Bengal and 2- Mercapto-ethanol tests performed by (18) was less accurate than the Indirect ELISA test.

On the other hand, more confirmatory tests in some epidemiological studies were used besides to confirmation of Brucella spp in culture (19). In our study, all the serum samples were examined by the Rose Bengal test, then the positive samples were confirmed using the competitive ELISA test. The c-ELISA test was used to overcome problems that came from residual antibodies, and cross-antigenicity between these bacteria and many Gram-negative bacteria (20). Serological tests are safe, rapid, and somewhat inexpensive diagnostic tools; Rose Bengal test, enzyme-linked immunosorbent assays, complement fixation test is advisable tests for large-scale eradication objectives (21,22).

ELISA test used in this study as suggested by (23) to confirm and avoid many problems of other serological tests (24). Also by using different serological tests, the variation between the results are depends on the serological test specificity and sensitivity. ELISA, low coast, quantitative, sensitive, but requires standardization of the antigen used. C-ELISA test has high sensitivity and specificity as a substitute to classical tests such as the Rose Bengal test, which is cannot differentiate between some strains like B. abortus strain 19 (25).

Conclusions

There is a presence of Brucella seropositive samples in different areas in Al-Najaf province, Iraq. The prevalence of the disease in the cattle older than 36 months was 5.81%. 40% of cattle herds were infected with the disease. There is no infection recorded in the males. The result of this work provides another screening information for Brucellosis in cattle and gives a better epidemiological saw that could be used for better control of such an essential disease in Iraq.

Acknowledgments

The authors would like to thank the staff of College of Veterinary Medicine at Kufa University for helping during research.

Conflict of interest

The authors declare that there are no conflicts of interest regarding the publication of this manuscript.