The little-known Shuni virus, capable of killing horses, should be monitored in case it expands into regions such as Europe and the Middle East, according to researchers.
It is described by researchers as a neglected re-emerging virus capable of infecting a range of animals. It is thought to be transmitted by blood-feeding insects.
Shuni virus was first isolated from a cow in Sokoto, Nigeria, in 1966. A human case, in a feverish child, was also detected in Nigeria the same year.
The virus was later recovered twice in South Africa, from mosquitoes and healthy cattle in 1972.
It has also been isolated from the brains of two horses — one from South Africa and the other from nearby Zimbabwe — in the 1970s. The virus was not further investigated until 2009 when surveillance for neurological insect-borne viruses in horses was implemented by University of Pretoria scientists.
They found evidence of the Shuni virus in 6% of horse cases which displayed severe neurological problems and fever, with an overall fatality rate of 42.9%.
Antibodies against the virus were subsequently identified in 3.9% of veterinarians involved in equine, wildlife and livestock services in South Africa, suggesting that human exposure may occur.
Thopisang Motlou, June Williams and Marietjie Venter, reporting in the journal Viruses, said they recently identified the virus in humans with neurological signs in hospitals in Gauteng Province.
Shuni virus was detected in 5% of cerebrospinal fluid samples from cases of unsolved neurological signs in patients.
This, they said, increases the importance of learning more about it as a potential zoonotic virus in Africa.
Shuni virus was also identified in malformed ruminants during an outbreak in Israel between 2014 and 2015, and neurological infections in cattle in 2019, suggesting it may have the capacity to emerge in new regions.
It has also been detected in Culicoides midges and Culex theileri mosquitoes in a historical vector survey in Africa, and recent studies in Europe suggest Culicoides biting midges have the potential to spread the virus.
Motlou and her colleagues said, despite the virus being detected on several occasions in Africa in the last 50 years, little is known about its epidemiology, its reservoir hosts, and its importance in human or animal disease.
For their study, they set out to learn more about its association with fever and neurological disease in horses over a 10-year period.
In total, samples from 24 of 1820 horses submitted to the zoonotic arbovirus surveillance program tested positive for the virus using molecular-based testing between 2009 and 2019, representing 1.3% of the animals.
Cases were detected in all provinces, with most (37.5%) occurring in Gauteng.
Neurological signs occurred in 21 of the 24 cases, with a fatality rate of 45.8%.
Gene testing identified strains previously identified in South Africa.
Full genome sequencing of a neurological case detected in 2016 showed 97.8% similarity to the South African strain, 97.5% similarity with the Nigerian strain, and 97.1% similarity to the 2014 Israeli strain.
“Our findings suggest that Shuni virus is circulating annually in South Africa and, despite it being relatively rare, it causes severe neurological disease and death in horses.”
Shuni virus poses a risk for transmission to other regions, they said, likely through migratory birds, other reservoir hosts and/or infected vectors.
“Shuni virus should be investigated as a cause of neurological disease in animals and humans in other African countries and monitored for expansion to new regions such as Europe and the Middle East,” they said.
Motlou and Venter are with the Zoonotic Arbo and Respiratory Virus Program at the Centre for Viral Zoonoses, which is in the Department of Medical Virology at the University of Pretoria. Williams is with the Department of Paraclinical Sciences at the university.
Motlou, T.P.; Williams, J.; Venter, M. Epidemiology of Shuni Virus in Horses in South Africa. Viruses 2021, 13, 937. https://doi.org/10.3390/v13050937