Examining Cache Valley virus research

Cache Valley virus: A scoping review of the global evidence. Waddell L*, Pachal N*, Mascarenhas M*, Greig J*, Harding S*, Young I, Wilhelm B. Zoonoses Public Health 2019 Jun 28. doi: https://doi.org/10.1111/zph.12621

This science story is based on collaborative work resulting in a scoping review on a mosquito-borne virus detected throughout North America, namely Cache Valley virus (CVV). The review identifies, characterizes and summarizes research on CVV, and identifies areas for further research, including the public health impact of CVV infection in human and animal populations.

What was known about this area prior to your work, and why was the research done?

Cache Valley virus (CVV) circulates in mosquito and animal species across a large area of North, Central, and South America. CVV infection has been associated with outbreaks of congenital defects in small ruminants in both Canada and the United States of America (USA). To date small ruminants are the only animals in which CVV‐associated clinical disease has been extensively studied. There are only six records of human CVV-associated illness that have been published, all acquired in the USA between 1995-2016. This scoping review looks at existing research on CVV and identifies research gaps.

What are your most significant findings from this work?

Based on the available research, it is unknown whether human illness of CVV is rare or rarely diagnosed. The six recorded human cases have all been severe and diagnosed via extensive testing. Testing is likely not pursued in less severe cases or in many clinical settings, particularly when other viruses that cause similar symptoms are also known to be circulating (e.g., West Nile Virus). Outbreaks in small ruminants in Ontario and Quebec, and seroprevalence surveys of humans and small ruminants in Manitoba and Saskatchewan over the last decade provide evidence that CVV is circulating in Canada.

Evidence of genetic mixing within CVV isolates and between related viruses has been reported from phylogenetic analyses. Observational studies and competence experiments have reported that a wide range of mosquito species are capable of CVV transmission. This is a unique observation to CVV as most mosquito-borne pathogens have one or two vector species responsible for the majority of pathogen transmission in a given area. Thus, the transmission cycle for CVV is not well defined and may be circulating within several mosquito and host species. This knowledge gap presents a challenge for both surveillance and the development of mitigation strategies.

What are the implications or impact of the research?

The compliment of CVV literature is small compared to other mosquito-borne pathogens and the scoping review identified a number of important knowledge gaps that require additional research. Improved awareness of the CVV as a possible cause of mosquito-borne illness may lead to the identification of additional cases and a better understanding of its impact on human and animal host populations.

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