Etude épidémiologique de la dermatose nodulaire contagieuse bovine en Ethiopie et évaluation de son impact économique

La dermatose nodulaire contagieuse (DNC) est une des maladies virales les plus importantes économiquement chez les bovins en Ethiopie. Elle est causée par le virus LSD (Lympy skin disease virus) appartenant au groupe des Capripoxvirus. L'objectif de cette thèse est de mieux comprendre l'épidémiologie de cette maladie afin de proposer des méthodes de contrôle et de prévention efficaces et applicables sur le terrain. Cette thèse est construite en cinq chapitres. Le premier chapitre fait une description générale du système de production agricole en Ethiopie et présente nos connaissances actuelles sur ce virus et cette maladie. Le second chapitre est consacré à l'évaluation d'un test d'immunofluorescence indirecte (IFI) pour le diagnostic sérologique à l'aide de méthodes sans gold standard. Le test de séroneutralisation virale a été utilisé comme second test de comparaison. L'analyse à l'aide d'un modèle bayesien a montré que l'IFI présentait une bonne sensibilité (92%) et une bonne spécificité (88%) ce qui suggère que ce test peut être utilisé pour le diagnostic et le dépistage de masse de la Dermatose Nodulaire Contagieuse avec une relativement faible proportion d'erreurs. La possibilité de tester un grand nombre de sérums en IFI est un autre avantage de cette technique pour conduire des études épidémiologiques de grande envergure. La sensibilité et la spécificité de la séroneutralisation virale (SNV) étaient respectivement de 78% et de 97%. En conséquence, le test IFI sera préféré pour un dépistage de masse en raison de sa meilleure sensibilité tandis que le test SNV sera réservé à la confirmation. Une étude épidémiologique transversale a été menée pour estimer la prévalence de la Dermatose Nodulaire Contagieuse Bovine à l'échelle du troupeau et de l'individu et pour définir les facteurs de risque associés à cette maladie dans le contexte particulier de l'Ethiopie. C'est l'objet de la troisième partie de cette thèse. Un total de 330 questionnaires d'enquêtes a été collecté de 44 associations paysannes situées dans 15 districts. La prévalence moyenne de la DNC à l'échelle du troupeau était de 42,8% (IC à 95% : 37,5 – 48,3). Elle était significativement plus élevée dans les zones d'altitude moyenne 55,2% (IC à 95% : 47,5 – 62,6) que dans les zones de basse altitude (22,3%) ou les zones de haute altitude (43,5%). La prévalence de la DNC et la mortalité due à cette maladie, observées à l'échelle de l'animal, étaient de 8,1% et de 2,12% respectivement. A nouveau, elles étaient plus élevées dans les zones d'altitude moyenne (10,4% et 3,2% respectivement) que dans les zones de basse et haute altitude (P < 0,05). L'analyse de facteurs de risque a montré que trois variables étaient significativement associées avec la prévalence de la DNC : l'effet de la zone agroclimatique, la conduite de troupeaux différents sur les mêmes pâtures et les mêmes lieux d'abreuvement et l'introduction de nouveaux animaux. L'incidence maximale de la DNC était concomitante de l'augmentation des populations d'insectes hématophages : cette association dans le temps était significative (coefficient de Spearman de 0,88 ; 0,79 et 0,79 respectivement pour les zones de haute, moyenne et basse altitude). L'évaluation de la faisabilité financière et des bénéfices espérés de la vaccination ont constitué la quatrième partie de la thèse. Le coût financier à l'échelle de la ferme des cas cliniques de DNC et le bénéfice économique de son contrôle par la vaccination ont été analysés dans cinq districts de la région Oromia. 747 questionnaires concernant une période de production d'un an ont été collectés. Des données d'épidémiologie descriptive ont été obtenues. L'incidence cumulée sur un an et les taux de mortalité ont été calculés pour chaque race, sexe et groupes d'âges. Le coût annuel des cas cliniques de DNC a été calculé en additionnant les pertes de production dues à la morbidité et à la mortalité. Les paramètres intervenant dans l'estimation des coûts financiers étaient les pertes de lait et de viande, la perte de capacité de travail (traction essentiellement) et les coûts de traitement et de vaccination. Le coût financier annuel par tête de bétail a été estimé à 6.43 dollars américains (USD) pour le zébu local et 58 USD pour les croisés Holstein dans les troupeaux infectés. La réduction des coûts financiers de la DNC par tête de bétail à l'aide d'un plan de vaccination annuel a été évaluée à 40% pour le zébu local et à 58% pour les bovins croisés Holstein. L'analyse comparative entre vaccination et absence de vaccination a permis de montrer que les producteurs locaux pourraient non seulement récupérer un bénéfice financier substantiel de la vaccination mais qu'ils pourraient également assurer la survie à long terme de leur élevage. Finalement, dans la cinquième partie sont présentées une discussion générale de l'étude épidémiologique et des moyens de contrôle ainsi que les questions non résolues qui nécessitent des efforts de recherche supplémentaires. Les résultats de l'étude des facteurs de risque pourrait également apporter des informations utiles pour la connaissance de l'épidémiologie de la DNC bovine dans d'autres pays africains. ABSTRACT : Lumpy skin disease (LSD) is one of economically important viral diseases of cattle in Ethiopia caused by Lumpy skin disease virus in the member of the genus Capripox viruses. The objective of this thesis is to better understand the epidemiological features of the disease in order to propose practical and applicable control and prevention options. The thesis is classified in five chapters. The first chapter describes the general agricultural production system in Ethiopia and relates the current knowledge on the virus and the disease as given by the literature.The second chapter deals with the performance of indirect fluorescence antibody test (IFAT) as a serological diagnostic and screening tool that was evaluated using methods without gold standard. Virus neutralization test (VNT) was used as the second test for comparison. The analysis of conditional dependent Bayesian model showed that the IFAT had good accuracy both in sensitivity (92%) and specificity (88%) parameters indicating that it could be used for LSD diagnosis and screening (epidemiological studies, epidemiosurveillance) with less misclassification. Its capacity to run large number of samples per plate just like ELISA could be also taken as an advantage for large epidemiological studies. The sensitivity and specificity of VNT was 78%, 97% respectively. The two tests IFAT and VNT were found conditionally independent on the disease status of the animal. Thus, higher sensitivity and throughput for IFAT would render the test being selected for screening purposes and higher specificity performance of VNT would qualify it to be used as a confirmation test. A cross sectional study was then conducted to estimate the prevalence of LSD at herd and animal-levels and to analyze the risk factors associated with the disease occurrence in Ethiopia. It is presented in the third chapter. A total of 330 questionnaire surveys were collected from 44 peasant associations (PA) distributed in 15 districts. The average herd level LSD prevalence was 42.8% (95% CI: 37.5–48.3) and it was significantly higher in the midland agro-climate 55.2% (95% CI: 47.5–62.6) than in lowland and highland agro-climate zones (22.3% and 43.5%, respectively). The observed LSD prevalence and mortality at animal level were 8.1% and 2.12% respectively which were still higher in the midland zone (10.4% and 3.2%, respectively) than in lowland and highland zones (P< 0.05). The risk factor analysis showed that three variables: the effect of agro-climates, communal grazing/watering management and introduction of new animals were significantly associated with LSD occurrence. The temporal association between LSD occurrence and increase in the biting-fly population was also positively correlated by Spearman rank correlation coefficient (0.88, 0.79 and 0.79 for highland, midland and lowland zones, respectively) and statistically significant. The need to evaluate the financial feasibility and benefit possibly expected of vaccination led us to the fourth component of the thesis: The financial cost of clinical LSD at the farm level and the economic benefit of its control by vaccination from the farmers' perspective were analyzed in five selected districts in Oromia Regional state, Ethiopia. A pre-tested questionnaire survey addressing the period of one year production cycle was considered and 747 questionnaires were collected. Descriptive epidemiological results were obtained from the questionnaire survey data. Annual cumulative incidence, mortality and case fatality rates were calculated for each breed, sex and age groups. Annual financial cost due to clinical LSD infection was calculated as the sum of the average production losses due to morbidity and mortality. The variables that accounted for financial cost estimation were milk loss, beef loss, traction power loss, and treatment and vaccination costs. Annual financial costs per head were estimated of 6.43 USD in local zebu and of 58 USD in Holstein Friesian (HF)/ crossbred cattle in infected herds. The financial benefit of controlling LSD through a one year planned vaccination was calculated using partial budget analysis and the changes in the enterprise outputs from the control intervention were measured from the variables milk production, beef production and draft work-output. The marginal rate of return (MRR) gained from the control intervention was estimated at 76 (7600%) and the net benefit per head was 3 USD and 33 USD in local zebu and HF/crossbreds cattle respectively. This implied that annual vaccination had enabled to reduce the financial costs due to LSD by 40% and 58% per head in local zebu and HF/crossbreds respectively. The analysis of the planned vaccination as compared to a non vaccination scenario for a one year time horizon have shown that the livestock producers would get substantial benefit not only from financial gain perspective but also to secure and maintain sustainable enterprise business. Finally in the fifth chapter, general discussion on the epidemiological study and control options were presented along with persistent knowledge gaps that requires further research efforts to finetune the proposed control and prevention options. The result from the risk factor analysis could also shed light on the epidemiology of LSD in other African countries suffering from the disease

Epidemiological Study of Lumpy Skin Disease and Its Economic Impact in Ethiopia

Lumpy skin disease (LSD) is one of economically important viral diseases of cattle in Ethiopia caused by Lumpy skin disease virus in the member of the genus Capripox viruses. The objective of this thesis is to better understand the epidemiological features of the disease in order to propose practical and applicable control and prevention options. The thesis is classified in five chapters. The first chapter describes the general agricultural production system in Ethiopia and relates the current knowledge on the virus and the disease as given by the literature.The second chapter deals with the performance of indirect fluorescence antibody test (IFAT) as a serological diagnostic and screening tool that was evaluated using methods without gold standard. Virus neutralization test (VNT) was used as the second test for comparison. The analysis of conditional dependent Bayesian model showed that the IFAT had good accuracy both in sensitivity (92%) and specificity (88%) parameters indicating that it could be used for LSD diagnosis and screening (epidemiological studies, epidemiosurveillance) with less misclassification. Its capacity to run large number of samples per plate just like ELISA could be also taken as an advantage for large epidemiological studies. The sensitivity and specificity of VNT was 78%, 97% respectively. The two tests IFAT and VNT were found conditionally independent on the disease status of the animal. Thus, higher sensitivity and throughput for IFAT would render the test being selected for screening purposes and higher specificity performance of VNT would qualify it to be used as a confirmation test. A cross sectional study was then conducted to estimate the prevalence of LSD at herd and animal-levels and to analyze the risk factors associated with the disease occurrence in Ethiopia. It is presented in the third chapter. A total of 330 questionnaire surveys were collected from 44 peasant associations (PA) distributed in 15 districts. The average herd level LSD prevalence was 42.8% (95% CI: 37.5–48.3) and it was significantly higher in the midland agro-climate 55.2% (95% CI: 47.5–62.6) than in lowland and highland agro-climate zones (22.3% and 43.5%, respectively). The observed LSD prevalence and mortality at animal level were 8.1% and 2.12% respectively which were still higher in the midland zone (10.4% and 3.2%, respectively) than in lowland and highland zones (P< 0.05). The risk factor analysis showed that three variables: the effect of agro-climates, communal grazing/watering management and introduction of new animals were significantly associated with LSD occurrence. The temporal association between LSD occurrence and increase in the biting-fly population was also positively correlated by Spearman rank correlation coefficient (0.88, 0.79 and 0.79 for highland, midland and lowland zones, respectively) and statistically significant. The need to evaluate the financial feasibility and benefit possibly expected of vaccination led us to the fourth component of the thesis: The financial cost of clinical LSD at the farm level and the economic benefit of its control by vaccination from the farmers' perspective were analyzed in five selected districts in Oromia Regional state, Ethiopia. A pre-tested questionnaire survey addressing the period of one year production cycle was considered and 747 questionnaires were collected. Descriptive epidemiological results were obtained from the questionnaire survey data. Annual cumulative incidence, mortality and case fatality rates were calculated for each breed, sex and age groups. Annual financial cost due to clinical LSD infection was calculated as the sum of the average production losses due to morbidity and mortality. The variables that accounted for financial cost estimation were milk loss, beef loss, traction power loss, and treatment and vaccination costs. Annual financial costs per head were estimated of 6.43 USD in local zebu and of 58 USD in Holstein Friesian (HF)/ crossbred cattle in infected herds. The financial benefit of controlling LSD through a one year planned vaccination was calculated using partial budget analysis and the changes in the enterprise outputs from the control intervention were measured from the variables milk production, beef production and draft work-output. The marginal rate of return (MRR) gained from the control intervention was estimated at 76 (7600%) and the net benefit per head was 3 USD and 33 USD in local zebu and HF/crossbreds cattle respectively. This implied that annual vaccination had enabled to reduce the financial costs due to LSD by 40% and 58% per head in local zebu and HF/crossbreds respectively. The analysis of the planned vaccination as compared to a non vaccination scenario for a one year time horizon have shown that the livestock producers would get substantial benefit not only from financial gain perspective but also to secure and maintain sustainable enterprise business. Finally in the fifth chapter, general discussion on the epidemiological study and control options were presented along with persistent knowledge gaps that requires further research efforts to finetune the proposed control and prevention options. The result from the risk factor analysis could also shed light on the epidemiology of LSD in other African countries suffering from the disease

Economic impact of lumpy skin disease and cost effectiveness of vaccination for the control of outbreaks in Ethiopia

Lumpy skin disease (LSD), an infectious viral disease of cattle, causes considerable financial losses in livestock industry of affected countries. A questionnaire survey with the objectives of determining direct economic losses of LSD (mortality loss, milk loss, draft loss) and treatment costs (medication and labour cost) per affected herd, and assessing the cost effectiveness of vaccination as a means for LSD control was carried out in the central and north-western parts of Ethiopia. From a total of 4430 cattle (in 243 herds) surveyed, 941 animals (in 200 herds) were reported to be infected. The overall morbidity and mortality at animal level were 21.2% and 4.5%, and at herd level these were 82.3% and 24.3%. There was a significant difference in animal level morbidity and mortality between categories of animals. Over 94% of the herd owners ranked LSD as a big or very big problem for cattle production. A large proportion (92.2%) of the herd owners indicated that LSD affects cattle marketing. A median loss of USD 375 (USD 325 in local Zebu and USD 1250 in Holstein-Friesian local Zebu cross cattle) was estimated per dead animal. Median losses per affected lactating cow were USD 141 (USD 63 in local Zebu cows and USD 216 in Holstein-Friesian local Zebu cross cows) and, USD 36 per affected ox. Diagnosis and medication cost per affected animal were estimated at USD 5. The median total economic loss of an LSD outbreak at herd level was USD 1176 (USD 489 in subsistence farm and USD 2735 in commercial farm). At herd level, the largest component of the economic loss was due to mortality (USD 1000) followed by milk loss (USD 120). LSD control costs were the least contributor to herd level losses. The total herd level economic losses in the commercial farm type were significantly higher than in the subsistence farm type. The financial analysis showed a positive net profit of USD 136 (USD 56 for subsistence farm herds and USD 283 for commercial herds) per herd due to LSD vaccine investment. It should be noted that only the noticeable direct costs and treatment costs associated with the disease were considered in the study. Generally, vaccination is economically effective and should be encouraged.</p

Molecular detection and phylogenetic analysis of Peste des petits ruminants virus circulating in small ruminants in eastern Amhara region, Ethiopia

Background: Peste des Petits Ruminants (PPR) is a severe, highly infectious and fatal viral disease of small ruminants. Four lineages of PPR virus have been identified globally based on sequence analysis of the nucleoprotein (N) and fusion (F) gene. The aim of this study was to isolate and genetically characterize recently circulating PPR virus in small ruminants in the eastern Amhara region in Ethiopia. A total of 28 anti-mortem samples (gum debris, nasal and ocular swab) were collected from clinically suspicious animals and examined for the presence of PPRV by a one-step RT-PCR assay. Samples positive with RT-PCR were subjected to isolation of the virus which were subsequently genetically characterized by sequencing of the nucleoprotein (N) gene and phylogenetic analysis of PPR virus (PPRV) strains. Results: Of the 28 clinical samples examined, 46.4% were positive with RT-PCR for viral nucleic acid. The PPRV was successfully isolated on CHS-20 cell line with the ovine signaling lymphocyte activation molecule (SLAM) receptor expressed on the cell surface and confirmed with RT-PCR and IFAT assay. The nucleotide sequence and phylogenetic analysis indicated that the PPRV obtained were clustered genetically with Lineage IV isolates of the virus. Conclusion: The successful isolation of the virus and molecular findings of this study confirmed active lineage IV PPRV infections among populations of sheep and goats in eastern Amhara, suggesting risks for potential spread of the disease to currently free areas. Thus, we recommend systematic vaccination to contain outbreaks in affected districts and geographically linked surrounding districts to which the disease could potentially spread due to different epidemiological linkages

Participatory epidemiological study on the burden of rabies in animals and humans in three districts of Buno Bedele Zone, West Ethiopia

Rabies is one of the priority zoonotic diseases and a major public health challenge in Ethiopia. Dog plays an important role in the transmission of the disease to humans. With this point in mind, this study was conducted in selected districts of Buno Bedele Zone namely Bedele, Gechi, and Dabo Hana districts, Western Oromia regional state from December 2019 to April 2020. The objective of the study was to know the status and burden of rabies in the community using the participatory approach and retrospective record assessment from animal and human health facilities. Twelve interview meetings were conducted in 12 Kebeles, which involved 156 informants. In this survey authors learned that dogs were the species most affected by rabies followed by cattle, human, cat, equine, and shoats. Accordingly, rabies in dog had an average score of 64 out of 100 with a range of 50-80. Besides, rabies outbreak was frequently noted between June to October in the study areas. Slaughter and sharing of the meat for household consumption was the most common practice taken to salvage bitten cattle. As per the available record in the study area, the estimated rabies cases incidence was 1.75 bovines, 18 dogs, 2.37 equines, 2.28 cats, and 0.37 shoats per 10,000 animals annually. The annual average post-exposure rabies vaccinations records were 75, 39, and 63 in Bedele, Dabo Hana, and Gechi districts, respectively. On the other hand, the average annual rabies death in humans was 2.2, 1.4, and 1.8 in Bedele, Dabo Hana, and Gechi districts, respectively. In general, this study shows that rabies is a disease that worth serious attention in the study areas

Field study on the use of vaccination to control the occurrence of lumpy skin disease in Ethiopian cattle

The current study was carried out in central and North-western parts of Ethiopia to assess the efficacy of Kenyan sheep pox virus strain vaccine (KS1 O-180) against natural lumpy skin disease (LSD) infection under field conditions by estimating its effect on the transmission and severity of the disease. For this study, an LSD outbreak was defined as the occurrence of at least one LSD case in a specified geographical area. An observational study was conducted on a total of 2053 (1304 vaccinated and 749 unvaccinated) cattle in 339 infected herds located in 10 sub-kebeles and a questionnaire survey was administered to 224 herd owners. Over 60% of the herd owners reported that the vaccine has a low to very low effect in protecting animals against clinical LSD; almost all of them indicated that the vaccine did not induce any adverse reactions. In the unvaccinated group of animals 31.1% were diagnosed with LSD while this was 22.5% in the vaccinated group (P < 0.001). Severity of the disease was significantly reduced in vaccinated compared to unvaccinated animals (OR = 0.68, 95% CI: 0.49; 0.96). Unvaccinated infected animals were more likely (predicted fraction = 0.89) to develop moderate and severe disease than vaccinated infected animals (predicted fraction = 0.84). LSD vaccine efficacy for susceptibility was estimated to be 0.46 (i.e. a susceptibility effect of 0.54) while the infectiousness effect of the vaccine was 1.83. In other words, the vaccine reduces the susceptibility by a factor of two and increases infectiousness by approximately the same amount. LSD transmission occurred in both vaccinated and unvaccinated animals, the estimated reproduction ratio (R) was 1.21 in unvaccinated animals compared to 1.19 in vaccinated ones, and not significantly different. In conclusion, KS1 O-180 vaccination, as applied currently in Ethiopia, has poor efficacy in protecting cattle populations against LSD, neither by direct clinical protection nor by reducing transmission, and this signifies the urgent need to either improve the quality of the vaccine or to develop potent alternative vaccines that will confer good protection against LSD.</p

Respiratory disease and sero-epidemiology of respiratory pathogens in the working horses of Ethiopia.

Pathogens are frequently implicated in equine respiratory disease. In Ethiopia, respiratory disease is a frequent cause for presentation at veterinary clinics and a priority concern for users of working horses. However, there is little existing literature on possible aetiologies.Determine prevalence of respiratory signs and exposure to major respiratory pathogens through a serological survey.Cross-sectional.Systematically selected horses from 19 sites in central Ethiopia were examined clinically and sampled once (August-December 2013). A face-to-face interview collected data on horses' management and history. Serological testing targeted equine influenza virus (EIV), equine herpesviruses-1 (EHV-1) and -4 (EHV-4), equine rhinitis viruses A (ERAV) and B (ERBV), equine arteritis virus (EAV) and Streptococcus equi subspecies equi (S equi).Owners reported a recent history of coughing in 38% of horses and nasal discharge in 7%. No animals were observed coughing during examination but 6% had a nasal discharge. Antibodies towards S equi, were most prevalent (8%, 33/350). Antibodies to EAV were confirmed in one animal (0.3%). Low antibody titres to EHV-1/4 and ERA/BV suggested prior exposure but antibodies to EIV were not detected. Multivariable, multilevel logistic regression analysis for risk factors associated with S equi serostatus showed higher odds of seropositivity in younger animals and those working less frequently.A single serological sample cannot describe dynamic changes in antibodies. Sampling horses at the place of work may result in healthy-worker bias.S equi may be endemic in this population and contributing, in part, to the occurrence of respiratory disease. Low prevalence of antibodies to viruses, with the exception of EIV, indicates these pathogens are present, but unlikely a predominant cause of respiratory signs and non-infectious causes of disease should also be investigated. Working horses in this region would be vulnerable to incursion of equine influenza. This article is protected by copyright. All rights reserved

Zoonotic tuberculosis in a high bovine tuberculosis burden area of Ethiopia

BackgroundTuberculosis (TB) is a major cause of ill health and one of the leading causes of death worldwide, caused by species of the Mycobacterium tuberculosis complex (MTBC), with Mycobacterium tuberculosis being the dominant pathogen in humans and Mycobacterium bovis in cattle. Zoonotic transmission of TB (zTB) to humans is frequent particularly where TB prevalence is high in cattle. In this study, we explored the prevalence of zTB in central Ethiopia, an area highly affected by bovine TB (bTB) in cattle.MethodA convenient sample of 385 patients with pulmonary tuberculosis (PTB, N = 287) and tuberculous lymphadenitis (TBLN, N = 98) were included in this cross-sectional study in central Ethiopia. Sputum and fine needle aspirate (FNA) samples were obtained from patients with PTB and TBLN, respectively, and cultures were performed using BACTEC™ MGIT™ 960. All culture positive samples were subjected to quantitative PCR (qPCR) assays, targeting IS1081, RD9 and RD4 genomic regions for detection of MTBC, M. tuberculosis and M. bovis, respectively.ResultsTwo hundred and fifty-five out of 385 sampled patients were culture positive and all were isolates identified as MTBC by being positive for the IS1081 assay. Among them, 249 (97.6%) samples had also a positive RD9 result (intact RD9 locus) and were consequently classified as M. tuberculosis. The remaining six (2.4%) isolates were RD4 deficient and thereby classified as M. bovis. Five out of these six M. bovis strains originated from PTB patients whereas one was isolated from a TBLN patient. Occupational risk and the widespread consumption of raw animal products were identified as potential sources of M. bovis infection in humans, and the isolation of M. bovis from PTB patients suggests the possibility of human-to-human transmission, particularly in patients with no known contact history with animals.ConclusionThe detected proportion of culture positive cases of 2.4% being M. bovis from this region was higher zTB rate than previously reported for the general population of Ethiopia. Patients with M. bovis infection are more likely to get less efficient TB treatment because M. bovis is inherently resistant to pyrazinamide. MTBC species identification should be performed where M. bovis is common in cattle, especially in patients who have a history of recurrence or treatment failure