An epidemiological study of the impact of Toxoplasma gondii and Brucella melitensis on reproduction in sheep and goats in Dohuk Province, Iraq

Ali Al-Hamada

Brucellosis and toxoplasmosis are very important zoonoses in many countries of the world, including Iraq. These diseases are considered economically important due to the negative effects on reproduction of small ruminants, which are a critical part of livestock enterprises in Iraq. Prior to the study outlined in this thesis, few studies on the epidemiology of brucellosis and toxoplasmosis and their effect on the reproduction in Dohuk Province had been undertaken. Consequently, the aims of the study were to determine the epidemiological characteristics, economic impact, and effect of brucellosis and toxoplasmosis on reproduction in small ruminants in Dohuk Province. A cross-sectional study of 432 small ruminants (335 sheep and 97 goats) belonging to 72 farms in six districts in Dohuk Province, northern Iraq, was undertaken to investigate risk factors associated with brucellosis seropositivity. Sera were tested using the Rose Bengal test (RBT) and an indirect enzyme-linked immunosorbent assay (iELISA). Using parallel interpretation, RBT and iELISA results showed that 31.7% (95% confidence interval (CI): 26.1, 36.3) of sheep and 34.0% (95% CI: 24.7, 44.3) of goats in the study had antibodies against Brucella. A random-effects multivariable logistic regression model indicated that a higher chance of being seropositive (odds ratio (OR) = 1.7; 95% 1.4; 2.2) was associated with an increase in the age of animals. The odds of Brucella seropositivity in flocks where sheep and goats grazed together was 2.0 times higher (95% CI: 1.08; 3.9) compared to flocks where sheep and goats grazed separately. The odds of Brucella seropositivity in small ruminants was 2.2 higher (95% CI: 1.2; 4.3) for animals originating from farms with a history of goat abortion in the preceding 12 months. In contrast, for every 1000 Iraqi Dinars (US$ 0.85) spent by the farmers on control of Brucella in their flocks, the odds of Brucella seropositivity decreased significantly (OR = 0.9, p-value = 0.021). The final model also indicated significant differences in Brucella seropositivity between the different districts of Dohuk province. The small ruminants were also tested for the presence of antibodies against Toxoplasma gondii, using a latex agglutinin test (LAT) and an indirect enzyme-linked immunosorbent assay (iELISA). When the test results were interpreted in parallel, 42.1% (95% CI: 36.7, 47.7) of sheep and 36.1% (95% CI: 26.6, 46.5) of goats were found to have antibodies against Toxoplasma. A multivariable logistic regression model was developed to determine the risk factors for Toxoplasma seropositivity in small ruminant flocks. Factors which increased the risk of infection included the presence of cats near the feed of animals (OR= 6.3; 95% CI 1.6, 24.6) and a history of abortions in sheep in the preceding 12 months (OR=13.4; 95% CI 2.1; 86.7). For every ten goats aborting in the preceding 12 months the odds of seropositivity increased significantly (OR=6.7; 95% CI 1.3; 32.9). In contrast, for every 1000 Iraqi Dinars (US$ 0.85) spent by the farmers on the prophylactic treatment in their flocks, the odds of Toxoplasma seropositivity decreased significantly (OR = 0.94; 95% CI 0.90, 0.98). Sera from 240 small ruminants (192 sheep and 48 goats) from 12 farms in Dohuk Province, northern Iraq, were collected to investigate relative risk of pregnancy loss associated with brucellosis and toxoplasmosis seroconversion during pregnancy. All the selected pregnant animals were examined by ultrasonography twice, at the time of blood collection (approximately 2 and 4 months of gestation). For detection of antibodies to Brucella, serum samples were tested using the Rose Bengal test (RBT) and an indirect enzyme-linked immunosorbent assay (iELISA), while the Latex agglutination test (LAT) and an indirect enzyme-linked immunosorbent assay (iELISA) were used to test for Toxoplasma gondii antibodies. There were significance differences in the seroprevalence in sheep and goats at the two sampling times for Brucella and Toxoplasma (P-value = 0.0003 and 0.03 in first and second sampling, respectively). The incidence risk of seroconversion to Brucella over the two months was 10.6% (95% CI: 6.9 -15.3) and 7.3% (95% CI: 4.3 - 11.6) for Toxoplasma. The analysis indicated that animals that seroconverted to Brucella were more likely to lose their pregnancy (OR: 2.9, 95%CI 1.6-5.5). An economic evaluation of mass vaccination programme for brucellosis indicated that the financial loss overall from brucellosis would decrease from 1.75 to 0.55 US$ per adult female. The net present value of the mass vaccination program was estimated at US$ 10,564,828 (95% CI: -16,203,454 to 37,049,245), the benefit-cost ratio was estimated to be 4.25 (95% CI: 0 to 11.22), and the internal rate return (IRR) was estimated at 91.38% (95% CI:11.71 to 190.62%). The seroprevalence in small ruminants was predicted to decrease from 9.22 to below 0.73 % after 20 years of the implementation of the proposed mass vaccination program. It is concluded that, identifying the putative risk factors for both pathogens with implementing a mass vaccination program of small ruminants with Rev. 1 for brucellosis will inform the development of more effective control programs to reduce the impact of the infection and advocate for adequate resources to implement the programs.

An epidemiological study of the impact of Toxoplasma gondii and Brucella melitensis on reproduction in sheep and goats in Dohuk Province, Iraq

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