Currently isolated to Africa, Madagascar and the Arabian Peninsula, RVFV is an acute mosquito-borne disease of ruminant animals that is transmissible to humans. Infected animals experience abortions and high levels of newborn mortality due to necrotic hepatitis. Humans experience flu-like symptoms and possible death.
Publishing their findings in April, CSU’s research team investigated the mosquito populations found at feedlots and surrounding areas in northern Colorado. The study determined which mosquito specie is of highest risk of transmitting RVFV.
“Our goal is to proactively gather information that will be important to controlling the spread of Rift Valley fever virus by mosquitoes, to make response efforts more targeted and effective,” says Dr. Rebekah Kading, researcher and assistant professor of microbiology, immunology and pathology at Colorado State University.
As one of the emerging global health concerns, RVFV has the potential to invade the U.S. as did West Nile and Zika viruses. Similarly, the disease could have devastating effects on animal and human health, as well as the economy, if introduced to the U.S. Therefore, mosquito species that are principally involved in transmission of those disease were the foci of Kading’s latest research.
By joining laboratory research and fieldwork, it was determined that Culex tarsalis mosquitoes are of primary concern. Commonly found in feedlots, this mosquito species readily blood feeds on cattle and will bite humans. Abundant in rural agricultural communities in the western U.S., these mosquitoes pose a threat not just to cattle and other ruminants, but also to humans as potential vectors of RVFV.
Transmission from animal to human can occur via mosquito bite or exposure due to handling infected animal tissues. Mosquito-borne transmission would require a mosquito to feed upon an infected animal or human with enough virus in the blood to infect the mosquito, which is as little as a few microliters.
Several other species of mosquitos were found to feed on livestock, but information about their ability to transmit RVFV is still being evaluated. Sheep and goats are also highly susceptible to the disease, and white-tailed deer are also proven to be at risk.
“By knowing what mosquito species would be important to spreading Rift Valley fever virus, we have a head start in knowing which species to target for surveillance and control,” Kading says.
While veterinary vaccines are available in Africa, safety concerns exist, so there are currently no licensed vaccines in the U.S. However, in July, CSU and the Coalition for Epidemic Preparedness Innovation (CEPI) announced a partnership dedicated to the development of a human vaccine. CEPI is dedicating $9.5 million to manufacture and preclinically study a single-dose vaccine for RVFV.
“We do these important studies so if, and when, Rift Valley fever virus does show up, we have a bit of a head start on how to control it,” Kading says.
Kading is also researching the ability of native Colorado mosquitoes to transmit RVFV by bite and the ability of the virus to pass from female mosquitoes to offspring. Additional research is also underway to characterize outbreak triggers, develop diagnostic tests and forecast how climate influences circulation and emergence of Rift Valley fever virus. 
Madison Anderson is a 2019 Progressive Cattle intern.
