Zoonotic viruses are viruses that have an animal reservoir but may also infect humans. The 2009 A(H1N1)pdm09 influenza pandemic, the SARS epidemic in 2003, the recent emergence of a novel coronavirus in the Middle East or the large epidemic of Ebola in West Africa are recent reminders of the global health threat posed by zoonotic viruses. Prior to widespread emergence in human populations, such pathogens can cause occasional infections in subpopulations that have been exposed to reservoir species (common reservoir species include for example bats, birds, swine, non-human primates). Whilst viruses causing such ‘‘spill-over’’ infections are usually poorly adapted for sustained human-to-human transmission, they are under strong selection pressure to increase transmissibility once in humans. If such adaptation occurs, a widespread epidemic is possible in humans.
Each time the world is confronted to a new emerging zoonotic virus, fast and sound risk assessment is therefore essential to inform policy making. Determining the transmission scenario is a key priority. Are we in a scenario where most human cases are being infected by the animal reservoir or can transmission in humans be self-sustaining? It is also important to assess the severity, in particular the proportion of cases that die. However, characterizing the transmission and severity scenarios at the start of emerging zoonotic virus epidemics may prove challenging because surveillance data are often scarce and biased (e.g. only a small proportion of cases are detected; severe cases are more likely to be detected than others) and because chains of transmission are imperfectly observed. Simon Cauchemez and his team have a long history of developing methods to overcome these problems.
Middle East Respiratory Syndrome Coronavirus (MERS-CoV)
The Middle East Respiratory Syndrome Coronavirus (MERS-CoV) was discovered in 2012. Since then, MERS-CoV has infected more than 1,500 persons, a third of whom died, essentially in the Middle East. People can get infected by direct or indirect contact with camels. Following an introduction, human-to-human transmission may occur and generate clusters of human cases. These clusters are often small although large outbreaks of MERS-CoV have also been documented in hospital settings. Overall, we still poorly understand the contribution of the animal reservoir and of human-to-human transmission to the build-up of MERS-CoV epidemics.
Saudi Arabia is the country that has been the most affected by MERS-CoV. In collaboration with the Saudi Ministry of Health, Imperial College and Johns Hopkins University, we analyze all the Saudi surveillance data on MERS-CoV to unravel the key drivers of MERS-CoV epidemic in the country. We also analyze data documenting the large MERS-CoV outbreak that recently occurred in South Korea in which more than 150 persons were infected.
Nipah in Bangladesh
Nipah is a bat-borne virus first identified in Malaysia in 1998, which has a high mortality rate in humans. Fruit bats are the natural reservoir host for the Nipah virus. Since 2001, it has caused deadly outbreaks every year in Bangladesh. The two major risk factors for transmission are person-to-person contact with a case and consumption of a local beverage (raw date palm sap). Bats can contaminate raw date palm sap when they lick date palm sap stream as it is collected in pots hanging in the trees overnight. In collaboration with icddr,b a research institute based in Bangladesh, we study climatic factors that affect the risk of a Nipah outbreak. We also investigate risk factors for human-to-human transmission.
- Cauchemez S, Fraser C, Van Kherkove M, Donnelly C, Riley S, Rambaut A, Enouf V, van der Werf S, Ferguson NM. Middle East respiratory syndrome coronavirus: quantification of the extent of the epidemic, surveillance biases, and transmissibility. Lancet Infectious Diseases 2014; 1:50-56.
- Cauchemez S, Epperson S, Biggerstaff M, Swerdlow D, Finelli L, Ferguson NM. Using Routine Surveillance Data to Estimate the Epidemic Potential of Emerging Zoonoses: Application to the Emergence of US Swine Origin Influenza A H3N2v Virus. Plos Med 2013; e1001399.
- Cauchemez S, Van Kerkhove M, Riley S, Donelly C, Fraser C, Ferguson NM. Transmission scenarios for Middle East Respiratory Syndrome Coronavirus (MERS-CoV) and how to tell them apart. Eurosurveillance 2013 ; 18:7-13.