Outbreak Investigation and Molecular Epidemiology of African Horse Sickness Virus Circulating in Central, Eastern and Southern Parts of Ethiopia
No Thumbnail Available
Date
2011-06
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Addis Ababa University
Abstract
This study was conducted from September 2009 to December 20 lOin central, eastem and
western patts of Ethiopia to investigate and identify circulating serotypes of African horse
sickness virus (AHSV). A total of ten outbreaks were investigated in the study period.
Samples collected for virus isolation and identification were whole blood in ethylene diamine
tetra-acetic acid (EDTA) from diseased horses and mules, and tissues from freshly dead
horses. AHSV isolation on Vero ce ll line and detection of AHSV genomes using conventional
RT-PCR were archived in the National Veterinary Institute (NY!) molecular laboratory,
Debre Zeit, Ethiopia. Samples were sent for further viral isolation, identification, sequencing
and phylogenetic analyses in the Non-vesicular Laboratories of Institute of Animal Health
(!AH), Pirbright, United Kingdom (UK). A total of 336 sera were collected from apparently
healthy equids that were either unvaccinated or have vaccination history of before three years
in Cheat and Tikur Inchini districts and subjected to a serological test using a commercialized
blocking enzyme linked immunosorbent assay (ELISA) kit. A questionnaire survey was
administered to 178 equine owners and retrospective data of outbreaks for three years
obtained from Animal and Plant Health Regulatory Directorate (APHRD) in the Ministry of
Agriculture (MoA) were analyzed to see the national picture and seasonality of outbreaks. A
total of 48 horses died of African horse sickness (AHS) during the outbreaks. Ada'a district
was the major outbreak site where the outbreak involved a number of towns and villages. A
total of 81 horses and 3 mules were affected and 46 (54.8%) of them demonstrated cardiac
form of the disease while the rest 30 (35.7%), 6 (7. 1%), 2 (2.4%) were affected by horse
sickness, pulmonary and mixed forms of AHS, respectively. Multiple serotypes of AHSVs
were identified from the submitted samples by quantitative real-time RT-PCR and
sequencing. AHSV-4, AHSV-6, AHSV-8 and AHSV-9 serotypes were identified.
Identification of A HSV -4, AHSV -6 and AJ-ISV -8 are reported for the first time in Ethiopia.
AJ-ISV -9 was the dominant serotype circulating in the outbreak areas. Serotypes identified
from the outbreaks were phylogenetically compared with the reference stains in IAH,
Pirbright, UK. A total of 147 (43.8%) of the sampled equids were found seropositive for
antibodies against AHSV. The respective seropositivity of equids in Cheat and Tikur Lnchini
districts were 49.4% and 37.8% (p= 0.032). Statistically significant difference was not
observed between risk factors of species, age and sex (p > 0.05). From the total 178
respondents 71 (40%) of them indicated that their indigenous knowledge on the disease, its
transmission and control measures is unsatisfactory while the rest (60%) were aware of the
disease. Local names used for AJ-IS were 'Derbetu ' or 'Dibe Ferda ' in Tikur Inchini and
'Horyo' in Cheta. Locally known equi ne flies were 'Bombisa ' in Tikur lnchini and 'Gemo'
and 'Yubo' in Cheta. A total of 482 outbreaks were recorded retrospectively from Oromia
(80.1 %), Amhara (10.6%), Southern Nati on Nationalities and People 's Regional State
(SNNPRS) (7.7%) and the rest from Tigray, Dire Dawa and Afar regional states. AHS
outbreaks were more frequently observed fi·OI11 September to December and the highest
number of outbreaks was reported in 2008. Generally, the identification of multiple serotypes
in the Crrnent study indicated increased risk and devastating outbreaks of AHS is a possibility.
The production of polyvalent vaccine which confers protection against the identified
serotypes and prophylactic vaccination of horses and mules are recommended.
Key words: African horse sickness virus, equine, Ethiopia, outbreak, RT-PCR, serotype.
Description
Keywords
African horse sickness virus, equine, Ethiopia, outbreak, RT-PCR, serotype.