Camels susceptible to MERS-CoV re-infection

Insight into the transmission of the virus causing Middle East respiratory syndrome (MERS) could help plan and evaluate preventive tactics against its spread between animals and to humans. In a KACST-funded study, researchers from King Faisal University in Saudi Arabia and Hong Kong University have found that camels infected by the MERS virus are susceptible to re-infection. The finding is relevant for the development of camel vaccination strategies to prevent transmission to humans.

MERS, whose symptoms include coughing, fever, shortness of breath, muscle pain, and gastrointestinal issues, was initially identified in humans during a flu outbreak in Saudi Arabia in 2012. Since then, it has spread to many other countries, such as the US and the United Kingdom, and has set off major outbreaks in Saudi Arabia, South Korea, and Kenya.

The infection is caused by a single-stranded RNA coronavirus (MERS-CoV) that is hosted in camels, which are the suspected source of transmission to humans. 

To better understand MERS-CoV and its mechanisms of transmission, a team, led by virologist, Malik Peiris, from The University of Hong Kong’s School of Public Health, monitored the existence and progression of MERS-CoV in two camel herds in the Eastern and Central provinces of Saudi Arabia between September 2014 and May 2015. 

MERS-CoV was not detected in any camels in the Eastern Province herd, which was housed and fed in a compound and had no contact with nomadic camels. MERS-CoV antibodies, however, were detected in all of the animals, indicating they had experienced a past infection. 

Evidence of an active MERS-CoV infection was found in nasal swabs from three camels in the Central Province herd, which was sometimes exposed to other camels and animals. The virus was not detected in rectal swabs from the same animals. Three other camels that did not test positive for the virus did show sequential elevations in MERS-CoV antibody levels, suggesting they had been re-infected following a previous infection. Genome sequencing of the detected viruses showed they were identical, indicating that a single virus was introduced to this herd. 

The team’s findings suggest that previous natural infection and passively acquired maternal antibodies do not fully protect the animals from reinfection. This raises questions about the duration of protection that infection or vaccines might give the animals, and about the relevance of camel vaccination as a means to restrict viral transmission between animals and, consequently, from animals to humans. Further studies are needed to investigate the effects of vaccination on the transmission of the virus among camels over longer periods.

1. Hemida, M. G., Alnaeem, A., Chu, D. K. W., Perera, R. A. P. M., Chan, S. M. S. et al. Longitudinal study of Middle East Respiratory Syndrome coronavirus infection in dromedary camel herds in Saudi Arabia, 2014–2015. Emerging Microbes & Infections 6, e56 (2017). | article