Molecular Characterization of Lumpy Skin Disease Virus Isolates from Outbreak Cases in Cattle from Sawena District of Bale Zone, Oromia, Ethiopia

Abstract

Lumpy skin disease (LSD) is a viral disease caused by LSD virus and is one of the most economically significant transboundary and emerging diseases of cattle. LSD causes considerable economic losses due to emaciation, damage to hides, infertility, and loss of milk production. In Ethiopia, the disease is distributed almost in all regions and is regarded as one of the most economically important livestock diseases in the country. An outbreak investigation of the disease was monitored from October 2016 to April 2017 in southern pastoral areas of Bale Zone, Oromia, Ethiopia. In December 2016, LSD outbreak occurred in Sawena district of Bale Zone, from which necessary biopsy samples were collected from actively infected animals for the purpose of virus isolation, and characterization using different molecular techniques at National Animal Health and Diagnostic Investigation Center (NAHDIC) of Sebeta, Ethiopia. In addition, clinical examination of infected and in-contact animals was carried out together with a questionnaire survey. Based on the clinical manifestations, LSD was recorded in 18% (94/522) of examined cattle, whereas biopsy samples from 20 clinically positive animals were collected for further laboratory process. The morbidity rate was higher in animals less than two years 28.97% (31/107) than other ages and showed a statistically significant difference with P < 0.05. Female animals showed higher morbidity rate of 20.59% (76/369) than male animals (11.76%) (18/153) with a significant difference at P ≤ 0.003. Mortality rate and case fatality were also significantly higher in young animals than other age groups. Viruses were isolated from both skin biopsies and nasal swabs on Vero cell line. From both skin biopsies and nasal swabs, the virus DNA was identified by amplifying the 172 bp DNA fragment using real-time and conventional PCR. Providing adequate diagnostic facilities, establishing strategic policies for effective control and eradication and awareness creations for communities for early identification or reporting were recommendations made to minimize economic losses of the disease.

Figure 1

Map of the study area.

Figure 2

An inflammation and whiteness of the eye of cattle infected with LSD. Encircled area shows lacrimation probably because of secondary bacterial complication.

Figure 3

Characteristic signs of LSD with generalized circumscribed skin nodules covering the entire body. Encircled area shows developed circumscribed nodules on the skin. Pictures were taken during field investigation.

Figure 4

LSD growth on Vero cell culture. (a) Uninoculated Vero monolayer cell after 24 hours. (b) Infected Vero cells showing typical CPE at 11^th day.

Figure 5

Classical PCR gel picture from skin nodule and nasal swabs of LSDV infected cattle. Lane M: DNA ladder (100bp, Fermentas); lanes 1–10 represent positive samples from Sawena district of Bale; N: negative control without template; P1: positive control for LSD; P2: positive control for SPP.

Figure 6

Melting curve analysis of field isolates of LSDV.

Figure 7

Picture taken during questionnaire survey in the study areas.