Rift Valley Fever

Rift Valley fever virus (RVFV), of the family Phenuiviridae, genus Phlebovirus, is an arthropod-borne pathogen of ruminants, endemic to sub-Saharan Africa and the Arabian Peninsula. RVFV contains a tripartite RNA genome consisting of a small (S), medium (M) and large (L) segment. RVF virions are spherical, consisting of an envelope and a ribonucleocapsid (RNP), measuring 80-120 nm in diameter. The viral envelope is covered by 122 capsomers, consisting of heterodimers of the glycoproteins Gn and Gc on an icosahedral lattice with T = 12 quasisymmetry.

There are numerous mosquito species capable of transmitting RVFV, of which Aedes are the main vector, while Culex, Anopheles and Mansonia play a minor but in any case important role in the development of outbreaks. Other arthropods such as midges, ticks, and phlebotomus can be infected with the virus and could potentially act as mechanical vectors.
A study of mosquitoes trapped during an epizootic identified more than 53 field-caught species that tested positive for RVFV, while more than 65 species are described as potential vectors, among them the vast majority of Aedes and Culex.
The majority of human infections are due to contact with blood or organs of infected animals, which can occur at different stages of farming, from animal care to slaughter. There is also the possibility, not yet established, that the disease can also be transmitted by drinking raw milk. More rare, but still possible, are transmission through mosquito bites and vertical transmission, from mother to fetus, both of which have been documented.
For livestock, direct transfer between animals appears to be rare or nonexistent, as demonstrated by early experiments showing that viraemic sheep fail to transfer the virus to other animals. Recent research has shown that sheep with acute RVFV infections in contact with highly susceptible immunocompromised lambs failed to transmit any virus.

The presence of Rift Valley fever is confirmed in almost all of sub-Saharan Africa, Egypt, Saudi Arabia and Yemen.Specifically, the U.S. CDC reports, monitoring the status of the disease, a breakdown into three risk categories in the region:

Countries reporting endemic diseases and substantial outbreaks of RVF	Egypt, Gambia, Kenya, Madagascar, Mauritania, Mozambique, Namibia, Saudi Arabia, Senegal, South Africa, South Sudan, Sudan, Tanzania, Yemen, Zambia, Zimbabwe
Countries reporting few cases, periodic virus isolation, or serologic evidence of RVF infection	Angola, Botswana, Burkina Faso, Cameroon, Central African Republic, Chad, Democratic Republic of Congo, Ethiopia, Gabon, Guinea, Mali, Niger, Nigeria, Republic of Congo, Somalia, Uganda
State RVF unknown	All other countries

Human infections can lead to a wide spectrum of clinical outcomes. Although most cases induce a febrile illness that resolves on its own, it is estimated that 1-2% of infections result in a much more severe illness, often with high levels of mortality.
After an incubation period of 2-6 days, clinical symptoms of RVF include fever, headache, back pain, dizziness, anorexia, and photophobia. The fever may last several days with a recovery period ranging from a few days to a month. Some patients experience a two-stage febrile illness, in which there is a reduction in symptoms around the third day before recrudescence 1-3 days later.
The severe form of RVF can include a wide range of manifestations such as hepatitis, jaundice, and hemorrhagic disease. Patients with hemorrhagic fever have a very high mortality rate and usually succumb within one to two weeks after the onset of symptoms.
Other symptoms may include photophobia, reduced vision, blind spots, uveitis, retinitis, and retinal hemorrhage. The duration of the disease varies from chronicity to resolution within a few weeks. It is estimated that ocular disease occurs in 2-5 % of mild RVFV infections, while the prevalence among those with severe disease can be more than 10 %.
Severe and lasting problems may also occur shortly after the initial symptoms disappear, including decreased consciousness, hallucinations, confusion, dizziness, excessive salivation, weakness, paralysis, decerebrate posture, and hemiparesis.

There are several methods for diagnosing acute RVFV infection in cattle and humans, but all must be performed in the laboratory.
One of these is the use of ELISA technique to detect IgM antibodies typical of a recent infection. Molecular RT-PCR methods can also be used to detect viral RNA, which are highly sensitive and specific. Virus can also be isolated by cell culture from blood samples taken during the febrile phase (or from organ samples taken postmortem).
Because most human infections are asymptomatic or cause flu-like illness, often the first sign of an RVF outbreak are near-simultaneous abortions in flocks of pregnant sheep called "abortion storms."

Most human cases of RVF do not require treatment. For patients with severe conditions, there is no specific treatment other than general supportive care, as there are no FDA-approved treatments for Rift Valley fever.
Treatment of symptoms such as fever and muscle pain can be done with standard over-the-counter medications. Care for hospitalized patients is supportive, including fluid replacement, avoiding all medications that liver, kidney, or coagulation.

1. The risk of contracting Rift Valley Fever is considered rare for international travelers. More at-risk travelers are classified as those who choose locations̀ rural and rather far from the usual tourist routes as their travel destination.
   
   No vaccine is available, so individual-level protections against mosquito bites remain essential. In endemic areas it is therefore recommended to:
   - wear light-colored clothing with long sleeves and long pants that cover most of the body;
   - avoid the use of perfumes;
   - apply insect repellents to exposed skin;
   - apply pyrethroid-based insecticides that can also be sprayed directly on clothing;
   - preferably stay in rooms equipped with an air conditioner.
   
   In areas affected by Rift Valley Fever outbreaks, contact with livestock, or wild animals, and their biological fluids should also be avoided. In case these contacts cannot be avoided, suitable protective equipment should be used.