Rift Valley Fever or RVF is a viral disease that primarily affects animals however it can also affect human beings. This viral zoonosis mostly infects domestic animals living in Sub-Saharan Africa including cattle, buffalos, goats, sheep, and camels. Though the severity rate of this disease is very low in human but when it occurs it can develop severe symptoms leaving major impacts on overall health.
A person can get RVF through direct contact of body fluids, blood, and tissues of infected animals or through biting of an infected mosquito from this virus. The human to human transmission rate and incidents are not documented any.
The incubation period for this viral disease varies from 2 to 6 days i.e. the interval period from the date you get this infection to the date when the onset of its symptoms occur. People who contract this infection usually do not develop any symptoms or develop a very mild form of feverish syndrome symptoms such as flu-like fever, headache, muscle pain, and joint pain.
Severe illness and symptoms are very common in animals infected with this disease however on a very small percentage of approx. 8 to 10% of cases people with RVF disease develop severe symptoms such as hemorrhage, encephalitis, and eye disease.
This viral disease is also known for causing significant economical losses out of the death and abortion cases among a huge number of RVF infected livestock or domesticated animals.
RVF virus belongs to the Phlebovirus Genus family which was first identified in the year 1931 during the investigation of an epidemic that occurred among sheep at a farm in Kenya’s Rift Valley. Since then this outbreak is continued and reported several years in sub-Saharan Africa. Other than this a major outbreak was reported in 1977 in Egypt which occurs due to trade of infected livestock.
Another explosive outbreak happened in 1997-98 in Kenya, Tanzania, and Somalia. The infected livestock trade from the horn of Africa spread RVF virus to countries like Saudi Arabia and Yemen in September 2000 which was the first incident of this disease reported outside of the African continent which increases the risk of spreading this disease to Asia and Europe as well through trading.
How RVF Transmission Occur in Humans
In the majority number of cases, humans get this infection through their direct or indirect contact with blood or tissues of infected animals. The transmission of RVF virus occurs during butchering or slaughtering while direct contact with animal tissues or organs.
Apart from this other close interaction with infected animals increases this virus transmission risk such as while assisting in animals' birth, performing veterinary works, and from the disposal of fetuses or carcasses. People belonging to special occupations have a greater risk of contracting this infection such as farmers, herders, veterinarians, and slaughterhouse workers.
Usually, the virus infects people through inoculation like through a wound from an infected tool (knife, etc), via any broken skin area, and through aerosols inhalation produced during the slaughtering of an infected animal.
Also, few evidences are there in which RVF transmission has occurred through the ingestion of uncooked or unpasteurized milk of an infected animal. Apart from these RVF virus transmission sources, humans can get this infection from the bite of infected mosquitoes usually from the Aedes and Culex mosquitoes and blood-feeding flies such as Hematophagous.
As of date, no human to human RVF virus transmission cases has been recorded nor any case of transmission of this virus has reported to the health care workers while they have used standard infection control precautions measures. Also, there is no evidence of RVF fever outbreak in any urban location.
Signs and Symptoms
River Valley fever has an incubation period of 2 to 6 days after exposure to the RVF virus. This can develop many different disease syndromes if symptoms appear. In most of the cases, RVFV infected people either do not develop any symptom or develop very mild feverish symptoms including fever, fatigue, back pain, dizziness, etc at the onset of symptoms. Most people recover just within two days to one week after the onset of their symptoms.
However, this doesn’t happen in the severe cases of RVF which occur to a very small percentage of total RVFV infection i.e. 8 to 10%. In such cases, the symptoms are more severe including-
This is an eye disease that sometimes develops with symptoms that occur in the mild cases of RVFV. Lesions occur on the eyes after 1 to 3 weeks of the onset of the initial symptoms with signs like blurry and reduced vision. In many cases, the lesions disappear within 10 to 12 weeks of its occurrence. However, the cases where lesion occurs in macula the center of retina approximate 50% of these cases end up with permanent vision loss.
Hemorrhagic fever occurs even less than one percent of total RVF cases. Its symptoms develop with jaundice and other liver impairment symptoms followed by bloody stool, bloody vomiting, or bleeding from nose, gums, skin and injection sites. These severe symptoms occur after 2 to 4 days of illness onset. The fatality rate in these cases is approx. 50% leading to death risk that usually happens after 3 to 6 days of hemorrhagic fever symptoms onset.
Encephalitis is an inflammation of the brain which can cause headaches, seizures and even coma. This happens even less than 1% of total RVF cases and onset happen after 1 to 4 weeks of first symptoms appear. The death cases are very rare in RVF patients who develop Encephalitis symptoms but it can badly impact their neurological health that may last for a very long period.
In the cases of River Valley fever that impacts animals, it leads to severe disease-causing symptoms like fever, weakness, spontaneous pregnancy loss and a very high rate of major illness and death, especially among animal babies. The RVFV infection causes abortion in 100% of livestock pregnancies which comes as an outbreak at different times. With comparison to young animals, the fatality rate is much lower among adult animals.
As the symptoms of Rift Valley fever are diverse and non-specific so its diagnosis is quite difficult. Especially in the initial stage of this disease, it is highly difficult to diagnose it. Also, it is difficult to differentiate Rift Valley fever and viral hemorrhagic fevers or any such diseases that develop symptoms similar to the RVF such as fever, muscle aches, headache, etc.
For the definite clinical result, testing is required however it is only available in reference laboratories. The laboratory specimens are very hazardous to use so it requires very safe and careful handling. The RVF virus can only be identified clinically by using below-mentioned laboratory tests-
- Reverse Transcriptase Polymerase Chain Reaction (RT-PCR) Assay
- IgG and IgM Antibody Enzyme-Linked Immunosorbent Assay (ELISA)
- Virus Isolation by Cell Culture
For most of the human Rift Valley fever cases, no specific treatment is needed to provide the affected patient because in general its symptoms are mild and for a very short duration. In the severe cases of RVF which lies around 8 to 10% of total human RVF cases, general supportive therapy in hospitals is the only way to cope up with its symptoms.
Though an inactivated vaccine has been discovered for human usage purpose but it is not clinically approved or licensed nor it is available commercially. The vaccine is only used as an experiment on veterinary and laboratory workers who have high exposure to RVFV for ensuring their health safety. For other people's usage purposes, the vaccine is under its investigation process.
Rift Valley fever is a major outbreak among animals causing a huge number of infected livestock death especially the young ones. However human is also the victim of this disease to some extent especially those who have direct interaction with infected animals body fluids etc. With the below-mentioned steps and measures, this disease growth risk can be prevented to a very great extent.
Prevention in Animals
The RVFV infection risks among animals can be prevented to a great extent with a sustained vaccination program for animals. Two effective vaccines have been developed for preventing the livestock RVF growth risk which is used by veterinarian doctors such as, modified live attenuated virus and inactivated virus vaccines.
Only one shot of live vaccine is enough to provide long-term immunity boost in animals. However, the usage of this vaccine is associated with the risk of spontaneous abortion if given to any pregnant animal. This side effect risk doesn’t exist with the usage of inactivated virus vaccine but this requires to be taken in multiple doses or shots in order to have complete protection from RVF which is very problematic for endemic regions.
The immunization of animals must be done before the occurrence of an outbreak to prevent an epizootic. This is because if animal vaccination implemented after the occurrence of an outbreak incident it increases the risk of intensifying this outbreak. During the mass animal vaccination campaigns healthcare workers may unintentionally transmit the RVF virus through reuse of needles or syringes and via the usage of multi-dose vials.
Also if in the herd of animals, some of them remain already infected with this virus or have not developed any symptoms yet for this disease the virus can easily be transmitted among other healthy animals resulting in the amplification of the outbreak. So these things must be considered proactively for preventing the spreading risk of RVFV among animals.
Restriction on livestock movement especially their international trade may prove effective in slowing down the outbreak initiation as well as expansion risk if already occurred.
Public Health Education for Risk Reduction
With public health education that increases the awareness regarding risk factors and RV virus spreading sources can reduce the RVF outbreak risks among humans. During an outbreak period close and unsafe contact with infected animal’s body fluids, directly or indirectly such as through aerosols are the most common reasons behind the transmission of this virus into the human body.
So these common risk factors can be eradicated significantly by creating awareness in the outbreak areas before this mishap actually occurs. Apart from this awareness is important regarding protective measures for people that can prevent their risk of interaction with RV virus spreading sources such as mosquito bites, unsafe contact with infected animal fluids, etc.
These public health education campaigns can play an effective role in preventing human infections and death rates caused by RVFV. The agenda that should be included and conveyed in public health education campaign for risk reduction includes-
- Avoiding the unsafe practices used during the slaughtering and animal husbandry practices. People who are indulged in these activities should wash their hands thoroughly and frequently, wearing hand gloves, and other protective gear should be used while handling any infected or sick animal and while handling animal’s tissues during slaughtering or while assisting in their baby birth process.
- Awareness should be created for reducing the risk of animals to human transmission of this virus that arises during the unsafe usage and consumption of animal tissue, fresh blood, and raw milk. In the epizootic areas, animal products such as milk, meat, and tissues should be well cooked before its intake.
- The awareness should be created for individual and community protection against RVF virus spreading risk through mosquito’s bites. People should wear long-sleeved clothing and of light color, should use homemade or commercial insect repellent and impregnated mosquito nets usage is a must. Also, people should avoid their outdoor activities during the peak season of mosquitoes breed and its biting.
Prevention in Health Care Settings
Though human to human RVF virus transmission cases have not been documented yet still there is a theoretical risk of spreading this virus from an infected patient to the healthcare workers via direct unsafe contact with infected blood, and tissues. So to prevent this virus transmission risk among healthcare workers who are taking care of either suspected or confirmed RVF patients, should follow standard precautions measures while handling specimens collected from patients.
Standard precaution is more precisely described as basic work practices needed to ensure a basic level of infection control or prevention. The Standard precaution measures are advised to implement in all cases of patient’s treatment and care irrespective of their suspected or confirmed disease status.
This includes safe handling of patient’s blood including dried blood, other bodily fluids or secretion and excretions excluding sweat irrespective of the fact that they contain visible blood or not and their contact with mucous membranes and non-intact skin.
Among the healthcare settings, laboratory workers are equally at risk just like hospital personnel. The samples that are collected from suspected human or animals for RVF virus detection should be handled with extreme care. The samples should only be handled by professional staff in a perfectly equipped laboratory.
Vector Control Measures
Through vector control, the Rift Valley Fever Virus spreading and its outbreak can be prevented to a great extent. By using protection measures against the vector bites people living in areas that are known for outbreak can easily protect them as well as their livestock lives.
In this context, Larviciding measures around the mosquitoes breeding sites are an effective step for vector control. However, for the successful result of this measure, it is important that the breeding sites are perfectly identified and the site is limited size and extent. The Larviciding measure often proves inefficient during the flooding seasons as in this duration the breeding sites are too high in number and extent that this measure proves infeasible.
Apart from these measures climate forecasting or predictions helps in preventing outbreak as some climatic conditions are favorable for the Rift Valley Fever or RVF outbreak based on past data and experiences of this infectious disease which is epidemic among animals but human are also not completely free from their hazardous risk if proper precautions are not maintained while handling livestock.