Testing the spread of MERS in camels

A natural infection model provides insights into how MERS spreads among camels and could be valuable in future vaccine trials

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If a vaccine became available, the widespread vaccination of camels against Middle East Respiratory Syndrome coronovirus (MERS-CoV) would help stem the spread of the disease in humans. Researchers at KAIMRC and across the Kingdom of Saudi Arabia have conducted a study to determine the prevalence of the virus in the nation’s camel population and develop a model of infection that will improve vaccination trials. 

Since the first human case in 2012, MERS-CoV has infected more than 2500 people in 27 countries, with outbreaks occurring largely in the Arabian Peninsula. The disease likely originated in bats, and dromedary camels are the only known intermediate host. 

“There is no vaccine against MERS-CoV for humans or camels yet,” says Naif Alharbi, director of KAIMRC’s Vaccine Development Unit. “MERS-CoV is endemic in the camel population in KSA, yet knowledge of how it spreads between camels and into humans is limited.”

Alharbi’s team collected serum samples from 362 young camels from the provinces of Al-Qassim and Al-Jouf. The team analyzed the samples for the presence of antibodies for MERS-CoV and found that 90 percent of the animals tested positive.

They then developed a model to try to better understand how the virus spreads. To do this, they brought five healthy, uninfected camels to a purpose-built, remote research farm. They then located infectious carrier camels in markets around KSA and brought them to the same farm.

The challenge was to bring the camels together during the small window of time when those carrying the virus were still infectious. “We had two or three days to source infectious camels, transport them hundreds of miles, and co-house them with healthy camels before they stopped being infectious,” says Alharbi. “Of course, human safety was of paramount importance, and we followed strict protocols throughout.” 

The model the team developed suggests that, with a ratio of one infected animal to two healthy ones in a farm, all the camels become infected within 24 to 48 hours. However, Alharbi stresses that more research is needed on the precise viral load required to trigger infection. Infected animals appeared free of viral symptoms after about two weeks. The team are now using their model to trial vaccines.

“Our model mimics natural infection, providing a realistic way of assessing new vaccine candidates,” says Alharbi. “Almost all endemic countries lack containment labs for large animals, so our facility and model are valuable resources.”

Alharbi’s team will continue their work with different vaccine candidates, fine-tuning doses and administration techniques to try to reach the best immune responses possible. The next challenge, he acknowledges, would be vaccinating all the camels in the region to curb the disease. 

References

  1. Alharbi, N.K. et al. Challenge infection model for MERS-CoV based on naturally infected camels. Virology Journal 17:77 (2020). | article

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