At the Biosecurity: Our Regional & National Response symposium on Monday in Kansas City, Mo., Barbara Drolet, PhD, USDA, ARS, Arthropod-Borne Animal Diseases Research Unit provided an update on Rift Valley Fever (RVF).
Rift valley fever is currently endemic in Africa. It has moved out of Africa to Yemen in 2000 where 100 people died, 800 became ill, and cattle, sheep and goats were affected. There are limited vaccines available in Africa and no vaccines for the U.S.
RVF is transmitted by floodwater mosquitoes that lay eggs, then floodwaters move the eggs, larvae emerge and an outbreak occurs with secondary mosquito vectors and the disease can be transmitted for the next 16-20 weeks.
Clinical signs appear within 2-6 days in newborns. There’s a 10-70% mortality in calves. Adults are weakened with diarrhea and abortions, but with less than 10% mortality.
Human exposure can occur through butchering, veterinarians performing necropsies, handling infected animals, etc. Transmission to humans via mosquitoes is controversial, but it can transmit through raw milk. It causes fever-type illness in humans and can have a10-13% mortality for those becoming ill. Overall mortality in humans is less than 1%.
It’s not known what might be the vectors of RVF in the U.S., but they are not the same as Africa. Is there interaction between RVF and other viruses? How will labs detect it? Samples may come in from an abortion storm, but by the time they realize it’s nothing they’ve seen before, it’s too late. There is no monitoring set up, no containment and no vaccines.
Drolet says there is development of vaccines and lab/field validating diagnostic assays and work at the BLS-2 level. “We will be able to tell the difference between vaccinate and infected.” But, Drolet notes, they are a long off on those diagnostic tests.
RVF is absolutely a threat to U.S. livestock and wildlife. “It could appear like WNV,” Drolet says. “It has consequences to animals and humans. It spreads easily by aerosol so there is potential for human infection. We’ve been slow to prepare for this virus.” She notes that various mosquitoes in U.S. are likely suitable hosts, and other vectors that are not native can spread it as well.
Economic losses due to animal loss, quarantines, trade restriction and an outbreak can be as high as $50 billion in the U.S.