Abstract
Bluetongue (BT) is an arthropod-borne viral disease of ruminants with serious trade and socio-economic implications. Although the disease has been reported in a number of countries in sub-Saharan Africa, there is currently no information on circulating serotypes and disease distribution in Zambia. Following surveillance for BT in domestic and wild ruminants in Zambia, BT virus (BTV) nucleic acid and antibodies were detected in eight of the 10 provinces of the country. About 40% (87/215) of pooled blood samples from cattle and goats were positive for BTV nucleic acid, while one hartebeest pool (1/43) was positive among wildlife samples. Sequence analysis of segment 2 revealed presence of serotypes 3, 5, 7, 12 and 15, with five nucleotypes (B, E, F, G and J) being identified. Segment 10 phylogeny showed Zambian BTV sequences clustering with Western topotype strains from South Africa, intimating likely transboundary spread of BTV in Southern Africa. Interestingly, two Zambian viruses and one isolate from Israel formed a novel clade, which we designated as Western topotype 4. The high seroprevalence (96.2%) in cattle from Lusaka and Central provinces and co-circulation of multiple serotypes showed that BT is widespread, underscoring the need for prevention and control strategies.
Highlights
Bluetongue (BT) is a non-contagious, but infectious notifiable arthropod-borne viral disease affecting wild and domestic ruminants, camelids and occasionally large carnivores [1,2]
The country-wide investigation into the epidemiology of BT was triggered by the unexpected detection of BT virus (BTV) nucleic acid in a blood-engorged Culex quinquefasciatus mosquito pool captured during routine surveillance for arboviruses in Zambia
Of the 259 pooled blood samples analyzed by qRT-PCR, 87 (33.6%) were positive for BTV nucleic acid (Table 2)
Summary
Bluetongue (BT) is a non-contagious, but infectious notifiable arthropod-borne viral disease affecting wild and domestic ruminants, camelids and occasionally large carnivores [1,2]. It is caused by the BT virus (BTV), a member of the family Reoviridae, genus Orbivirus. BTV possesses a double-stranded RNA genome consisting of 10 segments that encode 7 structural (VP1–VP7) and 5 non-structural proteins (NS1, NS2, NS3/NS3a, NS4 and NS5) which are packaged in a three-layered icosahedral protein capsid [7,8,9]. The outer capsid layer is composed of VP2 and VP5 proteins, encoded by genome segments 2 and 6, respectively. The VP2 and VP5 proteins induce neutralizing antibodies with the former being the major determinant of virus serotype [7]
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