Goat flock abortion: a retrospective study at Abergelle Agricultural Research Center, Tigray, Ethiopia.

BACKGROUND: Small ruminants are the principal component of livestock production in Tigray region, Ethiopia. But their productivity is affected by various factors. According to farmers and expert observation, goat abortion is among the leading causes of production losses in Tanqua-Abergelle district. However, study findings that examine the extent of distribution and economic impact of abortion cases in goats in the district are scarce. This retrospective study investigated the occurrence of abortion and its associated risk factors in three goat breed types at Abergelle Agricultural Research Center goat breeding site over a seven year period. The study included a total of does above one year old, and data were collected from a casebook that was specifically prepared for abortion cases. A thorough follow up was conducted to identify abortion cases. Additionally, a community survey was conducted in selected villages where the research center is located. RESULTS: The overall abortion proportion was 29.8% in the goat farm. Begait goat breeds had the highest abortion proportion (50.9%, CI 0.36-0.64) in 2015/16. Multivariate logistic regression analysis identified year, season, age and breed as major risk factors of abortion occurrence at flock level. Accordingly, the likelihood of goats experiencing abortion during the dry season (proportion = 34) was 1.87 times higher compared to those in the wet season (proportion = 22.8). Begait breeds had a higher incidence of abortion (proportion 37.5%, OR 4.87, CI 2.49-10.35) compared to other breeds. Age was negatively associated with abortion, suggesting that older goats (OR = 0.67) had a higher relative risk than younger goats (OR = 0.57). Moreover, the study noted a high incidence of abortion during the years 2014/15 to 2016/17 (proportion = 35.7-39.7). Within-breed analysis revealed that age and season were significant risk factors for Abergelle and Begait breeds, respectively by using a multivariate logistic regression analysis. A community survey indicated that 89.7% households responded their goats experienced abortion. CONCLUSIONS: This study highlighted the high prevalence of goat abortion at Abergelle and identifies important risk factors associated with its occurrence. The findings can inform targeted interventions to reduce abortion rates and improve goat productivity in the district.

Prevalence and Risk Factors of Bovine Mastitis in Southern Zone of Tigray, Northern Ethiopia.

Mastitis is the most common disease of adult dairy cattle. The disease continues to be one of the most perplexing and costly diseases of dairy cattle. The present study was conducted to detect bovine mastitis cows and identify potential risk factors for the distribution of bovine mastitis of smallholder dairy farmers using the California mastitis test. A cross-sectional study was conducted from September 2013 to May 2015 in the southern zone of Tigray, Northern Ethiopia, on 146 head of randomly selected cattle, of which 99 (67.8%) were crossed zebu and 47 (32.2%) pure local zebu using the California mastitis test and questionnaire. The overall prevalence was 65 (45.5%), of which 72.3% of crossed local and 27.69% of local zebu were found positive for the CMT test. The investigated risk factors were the season of lactation (OR = 0.510, CI = 0.208-1.247, P=0.140), washing hands between consecutive milking events (OR = 0.354, CI = 0.146-0.856, P=0.021), and history of previous mastitis (OR = 0.441, CI = 0.226-0.858, P=0.016), which had significant (P < 0.05) effect on the present prevalence of bovine mastitis in the study area. A high prevalence of bovine mastitis was observed in the southern zone of Tigray. The summer season of lactation and not washing hands between consecutive milking of cows were significant mastitis causation risk factors in addition to the history of previous mastitis disease history.

Generation and Evaluation of an African Swine Fever Virus Mutant with Deletion of the CD2v and UK Genes.

African swine fever (ASF) is a highly contagious and often lethal disease caused by African swine fever virus (ASFV). ASF emerged in China in August 2018 and has since rapidly spread into many areas of the country. The disease has caused a significant impact on China's pig and related industries. A safe and effective vaccine is needed to prevent and control the disease. Several gene-deleted ASFVs have been reported; however, none of them is safe enough and commercially available. In this study, we report the generation of a double gene-deleted ASFV mutant, ASFV-SY18-∆CD2v/UK, from a highly virulent field strain ASFV-SY18 isolated in China. The results showed that ASFV-SY18-∆CD2v/UK lost hemadsorption properties, and the simultaneous deletion of the two genes did not significantly affect the in vitro replication of the virus in primary porcine alveolar macrophages. Furthermore, ASFV-SY18-∆CD2v/UK was attenuated in pigs. All the ASFV-SY18-∆CD2v/UK-inoculated pigs remained healthy, and none of them developed ASF-associated clinical signs. Additionally, the ASFV-SY18-∆CD2v/UK-infected pigs developed ASFV-specific antibodies, and no virus genome was detected in blood and nasal discharges at 21 and 28 days post-inoculation. More importantly, we found that all the pigs inoculated with 104 TCID50 of ASFV-SY18-∆CD2v/UK were protected against the challenge with the parental ASFV-SY18. However, low-level ASFV DNA was detected in blood, nasal swabs, and lymphoid tissue after the challenge. The results demonstrate that ASFV-SY18-∆CD2v/UK is safe and able to elicit protective immune response in pigs and can be a potential vaccine candidate to control ASF.

Current status and evolving approaches to African swine fever vaccine development.

African swine fever (ASF) is a highly lethal haemorrhagic disease of swine caused by African swine fever virus (ASFV), a unique and genetically complex virus. The disease continues to be a huge burden to the pig industry in Africa, Europe and recently in Asia, especially China. The purpose of this review was to recapitulate the current scenarios and evolving trends in ASF vaccine development. The unavailability of an applicable ASF vaccine is partly due to the complex nature of the virus, which encodes various proteins associated with immune evasion. Moreover, the incomplete understanding of immune protection determinants of ASFV hampers the rational vaccine design. Developing an effective ASF vaccine continues to be a challenging task due to many undefined features of ASFV immunobiology. Recent attempts on DNA and live attenuated ASF vaccines have been reported with promising efficacy, and especially live attenuated vaccines have been proved to provide complete homologous protection. Single-cycle viral vaccines have been developed for various diseases such as Rift Valley fever and bluetongue, and the rational extension of these strategies could be helpful for developing single-cycle ASF vaccines. Therefore, live attenuated vaccines in short term and single-cycle vaccines in long term would be the next generation of ASF vaccines.

Generation and Immunogenicity of a Recombinant Pseudorabies Virus Co-Expressing Classical Swine Fever Virus E2 Protein and Porcine Circovirus Type 2 Capsid Protein Based on Fosmid Library Platform.

Pseudorabies (PR), classical swine fever (CSF), and porcine circovirus type 2 (PCV2)-associated disease (PCVAD) are economically important infectious diseases of pigs. Co-infections of these diseases often occur in the field, posing significant threat to the swine industry worldwide. gE/gI/TK-gene-deleted vaccines are safe and capable of providing full protection against PR. Classical swine fever virus (CSFV) E2 glycoprotein is mainly used in the development of CSF vaccines. PCV2 capsid (Cap) protein is the major antigen targeted for developing PCV2 subunit vaccines. Multivalent vaccines, and especially virus-vectored vaccines expressing foreign proteins, are attractive strategies to fight co-infections for various swine diseases. The gene-deleted pseudorabies virus (PRV) can be used to develop promising and economical multivalent live virus-vectored vaccines. Herein, we constructed a gE/gI/TK-gene-deleted PRV co-expressing E2 of CSFV and Cap of PCV2 by fosmid library platform established for PRV, and the expression of E2 and Cap proteins was confirmed using immunofluorescence assay and western blotting. The recombinant virus propagated in porcine kidney 15 (PK-15) cells for 20 passages was genetically stable. The evaluation results in rabbits and pigs demonstrate that rPRVTJ-delgE/gI/TK-E2-Cap elicited detectable anti-PRV antibodies, but not anti-PCV2 or anti-CSFV antibodies. These findings provide insights that rPRVTJ-delgE/gI/TK-E2-Cap needs to be optimally engineered as a promising trivalent vaccine candidate against PRV, PCV2 and CSFV co-infections in future.

Establishment of an Efficient and Flexible Genetic Manipulation Platform Based on a Fosmid Library for Rapid Generation of Recombinant Pseudorabies Virus.

Conventional genetic engineering of pseudorabies virus (PRV) is essentially based on homologous recombination or bacterial artificial chromosome. However, these techniques require multiple plaque purification, which is labor-intensive and time-consuming. The aim of the present study was to develop an efficient, direct, and flexible genetic manipulation platform for PRV. To this end, the PRV genomic DNA was extracted from purified PRV virions and sheared into approximately 30-45-kb DNA fragments. After end-blunting and phosphorylation, the DNA fragments were separated by pulsed-field gel electrophoresis, the recovered DNA fragments were inserted into the cloning-ready fosmids. The fosmids were then transformed into Escherichia coli and selected clones were end-sequenced for full-length genome assembly. Overlapping fosmid combinations that cover the complete genome of PRV were directly transfected into Vero cells and PRV was rescued. The morphology and one-step growth curve of the rescued virus were indistinguishable from those of the parent virus. Based on this system, a recombinant PRV expressing enhanced green fluorescent protein fused with the VP26 gene was generated within 2 weeks, and this recombinant virus can be used to observe the capsid transport in axons. The new genetic manipulation platform developed in the present study is an efficient, flexible, and stable method for the study of the PRV life cycle and development of novel vaccines.

Estimated prevalence and risk factors associated with clinical Lumpy skin disease in north-eastern Ethiopia.

Lumpy skin disease (LSD) is one of the major livestock disease problems in most areas of Ethiopia. A questionnaire-based cross-sectional study was conducted from October 2011 to February 2012 in four selected districts of Afar and Tigray regions to estimate the herd-level prevalence of LSD, and to assess its associated risk factors. Herd-owners were selected based on the willingness to provide information to complete the questionnaire. A total of 393 questionnaires were collected. Out of 393 herd-owners, 173 reported having LSD in their herds, giving an estimated herd- and animal-level prevalence of (44%, 95% CI: 37-50%) and (7.4%, 95% CI: 6-8%), respectively. Herd prevalence between regions and among the districts were significantly different (χ(2)=8, P<0.01 and χ(2)=9.9, P<0.01), respectively. The risk factors of LSD occurrence were introduction of a new animal to the herd, herd size, and utilization of communal grazing and watering points. These management characteristics cannot be readily changed in the studied area, hence, disease control should rely on a greater use of effective LSD vaccines.

Sero-prevalence and risk factors study of brucellosis in small ruminants in Southern Zone of Tigray Region, Northern Ethiopia.

This study reports a prevalence and risk factor survey of brucellosis in small ruminants in Southern Zone of Tigray Region, Northern Ethiopia between October 2011 and April 2012 to determine the sero-prevalence of small-ruminant brucellosis and to identify associated risk factors for the occurrence of disease in small ruminants under extensive production system. Multistage random sampling was followed to select locations, flocks, and individual animals. Laboratory analysis of serum samples provided sero-prevalence estimates for flocks and geographic location. Information on risk factors at the individual and flock level was obtained by examination of individual animal and a questionnaire interview to flock owners. The overall individual animal-level sero-prevalence of brucellosis in small ruminants was 3.5 % and flock level sero-prevalence was 28.3 %, and the within-flock sero-prevalence was ranged from 0 % to 22.2 % based on the Complement Fixation Test. Multivariable logistic regression showed that the major risk factors for flock level sero-positivity were flock size and abortion history. This study showed that small-ruminant brucellosis is prevalent in the study area. Larger flock size and history of previous abortion in the flock were major risk factors identified for sero-positivity of small-ruminant brucellosis.