important facts
Rift Valley Fever (RVF) is a viral zoonotic disease that primarily affects animals, but can also infect humans. Most human infections occur through contact with the blood or organs of infected animals. Infection in humans can also occur through the bite of an infected mosquito. To date, no human-to-human transmission of RVF virus has been recorded. The incubation period (the interval between infection and onset of symptoms) for RVF is 2 to 6 days. Epidemics in animals can be prevented. Through an ongoing program of animal vaccination.
overview
Rift Valley fever is a viral zoonotic disease that primarily affects animals, but can also be transmitted to humans. Infection can cause serious illness in both animals and humans. The disease causes significant economic losses due to mortality and abortion of RVF-infected livestock.
RVF virus is a member of the genus Phlebovirus. The virus was first identified in 1931 during an investigation into an epidemic among sheep in the Great Rift Valley of Kenya.
Since then, outbreaks have been reported in sub-Saharan Africa. In 1977, an outbreak was reported in Egypt, where the RVF virus was introduced through the trade of infected livestock along the Nile River irrigation system. In 1997-1998, large-scale infectious disease outbreaks occurred in Kenya, Somalia, and Tanzania following the El Niño phenomenon and large-scale flooding. RVF spread to Saudi Arabia and Yemen in September 2000 after trade in infected livestock from the Horn of Africa, marking the first reported outbreak of the disease outside the African continent and potentially spreading to other parts of Asia and Europe. Concerns arose that there was a sex problem.
Vector and host animal
Ecology and mosquito vectors
Several species of mosquitoes act as vectors of transmission of the RVF virus. The primary vector species vary by region, and different species may play different roles in sustaining virus transmission.
Among animals, the RVF virus is primarily spread by the bite of infected mosquitoes, primarily Aedes mosquitoes. Mosquitoes acquire the virus by eating infected animals. Female mosquitoes are also capable of transmitting the virus directly to their offspring via their eggs, which then hatch into a new generation of infected mosquitoes.
RVF virus in host animals
RVF virus infects many animal species and causes severe disease in livestock such as cattle, sheep, camels, and goats. Sheep and goats appear to be more susceptible than cows and camels. Outbreaks of RVF in animals often manifest as a wave of unexplained abortions in livestock and can mark the beginning of an epidemic.
Analysis of large-scale RVF outbreaks shows two ecologically distinct situations.
Main focus area. RVF virus persists through vector-host transmission and is maintained through vertical transmission in Aedes aegypti. Spread to secondary lesions. Once a major outbreak occurs in a major focal point, the disease can spread through livestock movements and passive dispersal of mosquitoes. This infection can be amplified within naive ruminants through locally competent mosquitoes such as Culex Culex, Mansonia spp., and Anopheles mosquitoes, which act as mechanical vectors. Irrigation facilities have large populations of mosquitoes throughout the year and are highly favorable locations for secondary disease transmission.
infection to humans
Most human infections occur through direct or indirect contact with the blood or organs of infected animals. The virus can be transmitted to humans through slaughter, handling animal tissue during slaughter, assisting in giving birth to animals, performing veterinary procedures, or disposing of carcasses and fetuses. Therefore, certain occupational groups, such as pastoralists, farmers, slaughterhouse workers, and veterinarians, are at increased risk of infection. There is some evidence that humans can become infected by consuming unpasteurized or uncooked milk from animals infected with RVF.
Human infection can also be caused by the bite of an infected mosquito, most commonly Aedes aegypti or Culex mosquito. Transmission of RVF virus by blood-sucking flies is also possible.
To date, no human-to-human transmission of RVF has been recorded, and no transmission of RVF to healthcare workers has been reported when standard infection precautions are implemented. .
human symptoms
The incubation period (the interval between infection and onset of symptoms) for RVF is 2 to 6 days.
Most human infections are asymptomatic or cause mild symptoms characterized by a febrile syndrome with sudden flu-like fever, muscle and joint pain, and headache. Some patients develop neck stiffness, photosensitivity, loss of appetite, and vomiting. In these patients, the disease can be mistaken for meningitis in its early stages.
Symptoms of RVF usually last 4 to 7 days, after which the immune response becomes detectable due to the appearance of antibodies and the virus disappears from the blood.
A small number of patients develop more severe disease. This usually manifests as one or more of the following three syndromes:
Ocular (ocular) type (0.5-2% of patients): Symptoms associated with mild disease are accompanied by retinal involvement. Eye lesions usually appear 1 to 3 weeks after the first symptoms. Patients report blurred or decreased vision. The disease may resolve on its own within 10 to 12 weeks. However, when lesions occur in the macula, 50% of patients experience permanent vision loss. Meningoencephalitis type (less than 1% of patients): Onset of meningoencephalitis type usually occurs 1 to 4 weeks after the first symptoms of meningoencephalitis occur. Introducing RVF. Clinical features include severe headache, memory loss, hallucinations, confusion, disorientation, dizziness, convulsions, lethargy, and coma. Neurological complications may appear after 2 months or more. Mortality is low in these patients, but severe neurological deficits are common. Hemorrhagic fever type (less than 1% of patients): Symptoms of this type appear 2 to 4 days after onset of illness. It begins with evidence of severe liver damage. Signs of bleeding may then appear, such as hematemesis, blood in the stool, purpura or ecchymosis, bleeding from the nose or gums, menorrhagia, or bleeding from the venipuncture site. The mortality rate for these patients is high, approximately 50%. Death usually occurs 3 to 6 days after symptoms appear.
diagnosis
Clinically differentiating RVF from other infectious diseases such as malaria, typhoid fever, bacteriosis, yellow fever, and other viral hemorrhagic fevers can be difficult, especially early in the course of the disease.
The following diagnostic methods are used to determine whether symptoms are caused by an RVF virus infection.
Reverse transcriptase polymerase chain reaction (RT-PCR) assay IgG and IgM antibodies Enzyme-linked immunosorbent assay (ELISA) Virus isolation by cell culture.
Samples taken from patients pose a very serious biohazard risk. Laboratory testing on non-inactivated samples should be performed under conditions of maximum biological containment. All non-inactivated biological specimens must be packaged using a triple packaging system for domestic and international transport.
Treatments and vaccines
Most human RVF cases are relatively mild and short-lived, so these patients do not require any special treatment. For more severe cases, the main treatment is early intensive supportive care, including fluid management and treatment of specific symptoms.
An inactivated vaccine has been developed for humans. However, this vaccine has not been licensed and is not commercially available. It is used experimentally to protect veterinarians and laboratory personnel who are at high risk of exposure to RVF. Other vaccine candidates are also being investigated.
prevention and control
Control of animal RVF
The occurrence of RVF in animals can be prevented by an ongoing program of prophylactic vaccination of animals. Both modified live-attenuated and inactivated virus vaccines have been developed for veterinary use.
To prevent animal outbreaks, animal vaccinations must be carried out before an outbreak. Once an outbreak occurs, vaccination of animals should not be carried out. This is because the use of multiple-dose vials and the reuse of needles and syringes poses a high risk of intensifying the outbreak.
Restricting or banning the movement of livestock can be effective in slowing the spread of the virus from infected to non-infected areas.
Because the occurrence of RVF in animals precedes cases in humans, establishing an active animal health surveillance system to detect new cases is essential to provide early warning to veterinarians and human public health authorities. .
Public health education and risk reduction
Raising awareness about the risk factors for RVF infection and the precautions individuals can take to avoid mosquito bites is the only way to reduce human transmission.
Public health messages for risk reduction should focus on:
Reduce the risk of animal-to-human transmission as a result of unsafe husbandry and slaughter practices. When handling sick animals or their tissues, or when slaughtering animals, practice hand hygiene, wear gloves and other appropriate personal protective equipment, and avoid using unsafe fresh blood, raw milk, or animal tissue. Reduces the risk of animal-to-human transmission resulting from ingestion. In animal endemic areas, all animal products (blood, meat, milk) must be thoroughly cooked before consumption. It is important to protect individuals and communities from mosquito bites through the use of impregnated mosquito nets, personal repellents where possible, and bright colors. By wearing clothing (long-sleeved shirts and pants) and avoiding outdoor activities during peak vector-biting hours, larvicide measures can be clearly identified and, if limited, taken in mosquito breeding areas. , exterminate vector insects. In size and scope. During periods of flooding, breeding sites are usually too numerous and extensive to implement larvicidal measures.
Infection control in medical settings
Although human-to-human transmission of RVF has not been proven, there is still a theoretical risk of virus transmission from infected patients to health care workers through contact with infected blood or tissue. Healthcare and laboratory personnel caring for patients with suspected or confirmed RVF should practice standard precautions when handling specimens collected from patients.
RVF predictions and climate models
Forecasting can predict weather conditions that are frequently associated with increased risk of outbreaks, potentially improving disease management. The occurrence of RVF in Africa, Saudi Arabia, and Yemen is closely associated with periods of above-average rainfall. In East Africa, it is closely related to the heavy rains that occur during the warm period of the El Niño/Southern Oscillation phenomenon.
RVF’s predictive models and early warning systems, using satellite imagery and weather/climate prediction data, can trigger the detection of zoonotic diseases in the early stages of an outbreak, allowing authorities to take action to avoid an outbreak. You can take this course.
WHO response
WHO is working with partners to support RVF surveillance, diagnostic capacity, patient care and outbreak response efforts in risk countries.
WHO is working with the Food and Agriculture Organization of the United Nations (FAO) and the World Office for Animal Health (WOAH) to improve predictions of human outbreaks and implement activities at the animal-human-ecosystem interface.
