Rift Valley Fever Virus
Samantha Hall
5/14/09

Abstract:
This paper covers information about causes, symptoms, treatment, and prevention of Rift Valley Fever Virus. Also provided is a brief history into the discovery and tracking of the virus.

Introduction:
Rift Valley Fever Virus is very interesting because it affect a comparatively small area in the world (3). While at least 10 species in North America have the potential to carry the virus, it is contained in Africa(5). It can be spread between humans and animals. In animals, it causes pregnant livestock to abort their fetuses.

Taxonomy:
Family: Bunyaviridae
Genus: Phlebovirus
Species: Rift Valley Fever Virus


Appearance:
Virions are enveloped. They are single-stranded RNA. They have three segments that are divided into their own nucleocapsid. Segments are referred to as (S) small, (M) medium, and (L) large.

RVF_Liver.jpg
Virions are entering into membrane vesicles in the cytoplasm of a liver cell of an infected rat.
Infection:
Rift Valley Fever Virus replicates mostly in the spleen, liver, and brain. This is especially true in fetuses. When the site has been infected it replicates very rapidly and in high concentration.

RVF_Brain.gif
This is replicating in an oligodendrogliocyte in the brain of a rat that was just beginning to show signs of RVF encephalitis.

Background Information:

Strain ZH 548 was isolated in Egypt in 1977. Rift Valley Fever was found in livestock by veterinarians. 200,000 people were infected and became ill. 598 people died from hemorrhagic fever.
In 1900s, it was discovered in Kenya. From 1997 to 1998 RVFV was found in Somalia and Kenya. In 2000, it was found in Yemen and Saudi Arabia, which was unusual because it was so much farther north than it is typically found.
By monitoring the areas where RVFV occurs, it was discovered that it occurs in areas with heavy rainfall. Standing water becomes a breeding ground for mosquitoes. Eggs can lie dormant for years. When it flood eggs of mosquitoes are then able to hatch and spread the virus. It is also common for outbreaks to occur in areas used to raise livestock.

africa_map.jpg
By closely monitoring the vegetation in the region affected by increased rainfall, scientists can identify the actual areas affected by outbreaks of Rift Valley Fever, a mosquito-borne disease that can be fatal to humans and animals. Scientists use satellite images to show regions of Africa that are greener (and wetter) than normal or more brown (and drier) than normal.
Transmission:
Infection of Rift Valley Fever Virus occurs in humans and other mammals, especially livestock. The virus can be transmitted in several different ways. The most common is by insect bites. Many species of mosquitoes and other blood sucking insects can carry the virus. It is usually carried in the Aedes Mosquitoes. RVFV can also be transmitted by the blood or bodily fluid of infected animals. People become infected this way by exposure by butchering, handling, or preparation of food. Contact with any blood, secretions, and excretion of infected animal may result in infection. RVFV has not been show to spread to animals in the absence of mosquitoes (arthropods).

Mosquito.jpg
Incubation period lasts from 2 to 6 days. Infection typically last from 1 to 7 days.

Fatality rates:
In humans, 1 percent of people that become infected with the Rift Valley Fever Virus have died. In livestock, less that 10 percent of adult cattle die, while between 10 to 70 percent of calves die. For goats and sheep fatality rate are much higher. Adult fatality rates are between 20 and 30 percent, while up to 100 percent of young may die from infection. 100 percent of fetuses are aborted in pregnant livestock when infected.

Symptoms:
Symptoms range from mild to severe. In mild cases, some patients show no symptoms. Other may experience fever, chills, nausea, vomiting, diarrhea, and abdominal pains. In severe cases, they may experience fever, loss of vision, severe headaches that could result in permanent brain damage, seizures, or occasionally go into a coma. They may also experience Jaundice, Hemorrhagic Fever, Encephalitis, Myalgias, Retinal Lesions, and Hemorrhaging. Severe cases can be placed into three categories: Meningoencephalitis which is infamation of the brain, spinal cord, and their Meninges, Retinitis (inflammation of the retina) with visual impairments, and Liver necrosis with hemorrhaging which causes localized death of liver cells and bleeding out.

Treatment:
There is no known treatment for animals. In humans, Ribavirin is used to treat for infection, however effectiveness is not known.
Prevention:
There are many things that can be done to prevent the spread of Rift Valley Fever Virus. Vaccinations can be done in areas of outbreak. A live strain is inserted into animals. The vaccine becomes effective in 6 to 7 days and can last up to 3 years. When pregnant livestock are injected with the vaccine it will result in abortion of the fetus. There is also an inactive vaccine that may be used in animals and humans. For animals, inactive vaccination requires two inoculations in order to become effective, which is less desirable in outbreak areas. The inactive vaccine for humans is still in the experimental phases. NASA also tracks the trends in heavy rainfall areas in order to predict were the next outbreak may occur.

Cow.jpg
Cow being vaccinated for Rift Valley Fever Virus.
Literature Cited:
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