Rift valley fever overview
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]Associate Editor(s)-in-Chief: Aakash Hans, MD[2]
Overview
Rift valley fever (RVF) is a zoonotic disease caused by the RVF Virus (RVFV) that mainly affects livestock and is responsible for illness in humans. The disease process in humans ranges from a simple febrile illness to fatal hemorrhagic conditions. Other symptoms include eye involvement and encephalitis. RVF is also known to have caused miscarriage in women. Mosquitoes, livestock and humans form parts of the virus’ life cycle. With a complex transmission process and lack of specific vaccines or treatment makes the disease difficult to control. Since mosquito breeding is an important factor for the spread of disease, regions with heavy rainfall are at risk to have increased numbers of cases and mortality.
Historical Perspective
In the year 1930, Rift Valley fever virus (RVFV) was discovered as the pathogen causing an increased incidence of hepatitis in animals belonging to the Rift Valley in Kenya.[1] The primarily affected animals were sheep, with deaths and miscarriages in sheep along with mortality in lambs born recently.
Classification
- There is no classification used for Rift valley fever.
Pathophysiology
RVF is transmitted to humans either via mosquito bite or via exposure to infected animals. There is no evidence of human to human transmission of the disease. The disease manifests in three major stages:
- Early infection
- It is mainly due to entry and survival of the virus in macrophages and dendritic cells.
- Liver infection
- The virus most commonly infects liver cells and causes inflammation via IL-10.
- Late infection
- The virus begins to invade neuronal cells leading to neurological symptoms.
Cause
Rift valley fever is caused by the Rift Valley fever virus (RVFV). The virus is a single-stranded RNA virus belonging to the Bunyaviridae family.
Differentiating Rift valley fever from other Conditions
The majority of differential diagnoses for RVF arise from other diseases which are prevalent in travelers and present with fever. All these disease would share a similar history of recent travel to an endemic area, followed by development of fever and body aches.
Epidemiology and Demographics
The virus is able to stay active outside the human body even when it is not being actively transmitted amongst animals. Heavy rain causes mosquitos to breed in large numbers, which translates into increased transmission to livestock. As more animals get infected, the risk of the virus being transmitted to humans increases. Humans acquire the infection by being exposed to animal fluids and products. Most of the disease surges till now have been seen in some regions of Africa and countries belonging to the Arabian peninsula. Since its discovery around the year 1930, there have been outbreaks of RVF, starting in the 1950 in the African countries, South Africa and Kenya.
Risk factors
Risk factors applicable to Rift valley fever are similar to other zoonotic diseases. Exposure to mosquitos feeding on infected animals is the main cause of acquiring the infection. All human activities and habits which expose them to mosquitos or the infected animals would qualify as risk factors of the disease.
Natural History, Complications and Prognosis
Rift valley fever is a self-limiting illness in majority of patients. The symptoms appear around 2-3 days after exposure. The main symptoms are fever and body aches. Fever usually subsides by 3-4 days after the beginning of symptoms. Complications can arise if the fever recurs again after remission and the patient continues to be febrile. Neurological, ophthalmological and hemorrhagic features are the commonly seen complications. Prognosis is good for most of the patients who only have the febrile illness which subsides on its own. The patients who suffer from complications usually recover at a slower pace out of which some succumb to the complications.
Diagnosis
Diagnosing Rift valley fever requires index of suspicion for individuals presenting with fever, especially after exposure to infected animals or mosquitos.
References
- ↑ Daubney R, Hudson JR, Garnham PC. Enzootic hepatitis or Rift Valley fever. an undescribed virus disease of sheep cattle and man from East Africa. J Pathol Bacteriol 1931; 34:545–579