Sunday, April 19, 2015

Get the Rift of it

Last Friday, I was showing some of the work I've done to my fellow Stanford School of Medicine Pediatrics Department-ites, and no one had heard of the virus I've been working with lately, so I decided to turn it into a blog post!

Since I've only been with my lab for a short time, I started working on a project that wouldn't take a lot of time to complete (you know, to prove myself to my lab -- "look, I've already finished a project!", ha!) before sinking my metaphorical teeth into some more substantial work. Luckily, it's turned into something I can present and publish.

So, let's talk about Rift Valley Fever!

The Great Rift Valley is a massive crack in the earth's crust (a.k.a. - "rift") that basically splits Kenya in two, from north to south. Rumor has it that the Great Rift Valley was discovered by a woman, but no one believed her.

In 1910, Kenya's Rift Valley region started seeing cases of pregnant livestock spontaneously aborting their offspring. This disease was the start of a long history with Rift Valley Fever Virus (RVFV), a Phlebovirus of the Bunyaviridae family. RVFV was eventually identified as a zoonotic agent, infecting people with contact with infected livestock. Mosquitoes were eventually identified as the vector for RVFV when incidence spiked after rainy seasons, as flooding increases potential breeding areas for mosquitoes.

Cows in Kenya - photo from Wildlife Direct
RVFV infections has been restricted to the African continent, primarily in western Africa, with a small outbreak reported in Egypt in 1977. In 2000, an RVFV outbreak was reported in Saudi Arabia and Yemen. The spread is usually a result of trading infected livestock and/or climate conditions that support the migration of mosquito populations.

RVFV is an enveloped, single-stranded RNA virus. The RVFV genome is divided into 3 segments of differing sizes (small, medium, and large), all of which are circularized. Host cells targeted during infection include macrophages, hepatocytes, and endothelial cells.

A computer modeled 3D structure of RVFV - image from Dr. Juha Huiskonen
Pathophysiology of RVFV in humans includes the standard headache, high fever, weakness, back pain, fatigue, and dizziness. Most people with these flu-like symptoms recover in about a week, and that's it. In severe cases, though, patients can develop encephalitis, retinitis, and hemorrhagic fever.

Given the severe affects on livestock reproductive viability, RVFV outbreaks can have devastating affects on the economy. Not only can you lose a large amount of your livestock population through death of the infected animal, and future generations by abortion, but once infected animals are identified, you are banned from trading livestock for an extended period of time. This process has been very effective in containing RVFV to the continent, but not all infected animals present symptoms prior to trade or breeding. With a large enough outbreak, severe economic collapse could follow.
An unfortunate casualty - Image from The Travel Doctor
There is a vaccine available to herders, but it can also cause the vaccinated animal to spontaneously abort developing offspring, although at a lower rate. Yet, it's difficult to convince herders to vaccinate their animals if they are (maybe) damned if they do and (likely) damned if they don't. There are also models that have successfully predicted RVFV outbreaks in the past.

The United States Department of Agriculture (USDA) has listed RVFV as a major threat to the U.S. because of the large economic dependency we have on livestock. Even though the virus has only started to leave Africa, the U.S. does have the vectors to support spread to North America.