SEROPREVALENCE AND RISK FACTORS OF THE MAIN ABORTIVE INFECTIOUS AGENTS OF CATTLE IN BATNA

Abstract

Infectious diseases are of increasing concern on dairy farms because of their potential impact on animal and human health, milk and meat production, food safety, and economics. The present PhD Thesis aimed to determine, at individual and herd level, the presence and risk factors of the main reproductive infectious agents of cattle in two regions from North Algeria: Batna, Khenchela, Setif (North-eastern) and Tiaret (North-western) Algeria respectively. The present Thesis is divided in three studies: Study-I analysed the prevalence and risk factors of the intracellular parasites Neospora caninum and Toxoplasma gondii; Study-II studied the prevalence and risk factors of the bacteria Chlamydia abortus, Coxiella burnetii and Brucella abortus; and Study-III analysed the prevalence and risk factors the Bovine Viral Diarrhoea Virus (Genus Pestivirus) and characterised molecularly the circulating strains. In Study-I, we conducted a cross-sectional serological study on dairy farms from North-eastern Algeria (Batna, Khenchela, Setif). Blood samples from 344 dairy cattle from 22 herds were collected. The presence of antibodies against N. caninum and T. gondii was assessed by two commercial indirect ELISA tests, while only 151 out of 344 sera belonging to 10 farms were tested for T. gondii antibodies. Also, the presence of N. caninum and T. gondii DNA in aborted foetuses from the same dairy farms was analysed by qPCR. In addition, the risk factors of neosporosis and toxoplasmosis were analysed. Prevalence of antibodies against T. gondii and N. caninum was 9.9 (15/151; 95 % CI=5.9-15.5) and 5.5 % (19/344; 95 % CI=3.3-8.4), respectively. At the herd level, the prevalence of antibodies against T. gondii and N. caninum was 70.0 (7/10; 95 % CI=34.7-93.3), and 59.0% (13/ 22; 95 % CI=36.3-79.2) respectively. Neospora caninum and Toxoplasma gondii DNA were detected in 30% and 0% of aborted foetuses, respectively. The analysis of risk factors showed that the number of calving (>=6 vs <=2) (OR=6.3; 95% CI=1.7-23.4), presence of horses (yes vs no) (OR=5.9; 95% CI=1.0- 35.9) and the use of artificial insemination in the last mating (yes vs no) (OR=4.8, 95% CI=1.17-19.90) were significantly associated with N. caninum prevalence in the studied cattle herds. Conversely, the presence of standing water in the pasture (yes vs no) (OR=0.2; 95% CI=0.05-0.8) was considered as a protective factor. Retention of foetal membranes (P=0.081), increased inter-calving period (P=0.096) and the clinical reproductive disorder experience (CRDE) (P=0.077) were the most frequently reported clinical reproductive disorders among T. gondii seropositive cattle. Study-II evaluated the seroprevalence and risk factors of the bacteria Chlamydia abortus, Coxiella burnetii and Brucella spp in dairy cattle from North-Eastern Algeria. Prevalence of antibodies against Brucella spp, Coxiella burnetii and Chlamydia abortus was 28.6% (127/437; 95% CI, 24.2-34.6%), 13.3% (46/344; 95% CI, 9.8-17.8%) and 1.45% (4/344, 95 % CI, 0.6-3.2), respectively. At a herd level Coxiella burnetii and Chlamydia abortus were observed in 11/22 (50.0%; 95% CI, 25.0-89.5%) and 4/22 (18, 1%; 95% CI, 5.0-46.6%) respectively. The following variables were identified as risk factors Abstract VI for Brucella spp prevalence by the final multivariable logistic regression analysis: age (all categories) for cows over 60 months of age (OR=7.39; 95% CI=2.1-25.5%), artificial insemination (OR=1.46; 95% CI=0.4-4.3%), and rivers in the pasture (yes vs no) (OR=25.9; 95% CI=8.2-81.7%). Herd size (as a numeric variable) was found as a protective factor, with an increase of one animal in the herd resulting in a decrease of a 4% (1-0.96=0.04) in the odds. Visitors entering farms without personal protective equipment (yes vs no) was the main variable that was identified as a risk factor for Coxiella burnetii prevalence by the final multivariable logistic regression analysis (OR=5.70; 95% CI=1.70-19.10). On the other hand, season (Autumn vs Winter vs Spring) and water source (tap water vs well) were identified as protective factors, with an odds ratio of 0.09 (95% CI=0.02-0.49) and 0.09 (95% CI=0.02- 0.44), respectively. The variables age (numeric), stray dogs (yes vs no), and presence of wild animals (mainly wolf, rodent, jackal, and Boar) in the building were identified as risk factors for Chlamydia abortus prevalence by the final multivariable logistic regression, with odds ratio of 1.03 (95% CI=1.00- 1.05), 0.05 (95% CI=0.00-0.85) and 13.75 (95% CI=1.57-120.64), respectively. In Study-III, we performed a cross-sectional seroprevalence study and evaluated the risk factors associated with BVDV on dairy farms from North-western Algeria. Blood samples from 234 dairy cattle from 31 herds were collected. Sera were analysed for the presence of antibodies against BVDV (Genus Pestivirus) using a commercial iELISA. The presence of Pestivirus RNA in sera was also analysed using a Reverse Transcription-qPCR and positive samples were sequenced. Additionally, we conducted a literature review of the presence of BVDV in ruminants in North Africa using a systematic search and compilation methodology to identify gaps of knowledge for future research. The prevalence of antibodies against Pestivirus at population (59.9%; 95% CI=49.0-70.7%) and farm (93.5%, 95% CI=78.6%-99.2%) level concur with epidemiological data reported in neighbouring countries. Risk factors associated with BVDV seroprevalence in cattle were mixed herd (presence of sheep in the farm), herd size (n>20), and parity (cow vs heifer). Furthermore, we confirmed the presence of BVDV-1a in Algeria. This study represents the first report of BVDV in cattle in Algeria (Tiaret province), on account of the fact that ruminant Pestivirus have historically been neglected pathogens in North Africa. Our results confirmed the presence of Neospora caninum, Toxoplasma gondii, Chlamydia abortus, Coxiella burnetii and Brucella spp, and BVDV among dairy cattle in Algeria and highlighted their negative impacts on animal health and production and their public health implications. Brucella spp and Toxoplasma gondii were found to cause reproductive disorders in the study area. A strong significant association was found between Brucella spp seroprevalence and abortion (P<0.001) in dairy cattle. The high BVDV prevalence and the presence of a potential Persistently Infected (PI) individual in the study area suggest an endemic epidemiological scenario of Pestivirus. Although Chlamydia abortus and Coxiella burnetii were found to be prevalent in the study area, with no Abstract VII association with reproductive disorders. The lack of epidemiological and molecular transboundary studies of abortive pathogens in ruminants in North Africa is of concern for human and animal health as well as for wildlife conservation and further research is warranted.