Rift Valley Fever Zoonotic Disease: All You Need to Know

Rift Valley fever zoonotic disease was first identified in 1931 during an outbreak investigation among sheep on a farm in Kenya’s Great Rift Valley. Since its discovery in 1931, RVF outbreaks have been observed across sub-Saharan Africa and, more recently, in the Middle East. The discovery of the RVF virus marked a significant milestone in understanding the complex relationship between animal health and human infections. This mosquito-borne illness belongs to the genus Phlebovirus within the family Bunyaviridae, which also includes other notable viruses such as yellow fever.

In eastern Africa, particularly East Africa and parts of the African continent where Culex mosquitoes are prevalent, RVF has become endemic due to favorable environmental conditions for its spread. These include heavy rainfall periods that lead to increased mosquito populations acting as vectors for transmitting the virus from infected animals to susceptible hosts like cattle, sheep, goats, camels, buffalo, and antelope species, as well as rodents like rats and mice.

• 1931: First identification of RVF during an epidemic among sheep in Kenya’s Great Rift Valley
• Late 20th century: Outbreaks reported across sub-Saharan Africa
• 2000 – present: Cases documented outside Africa; notably Saudi Arabia and Yemen

The history of Rift Valley Fever has been well documented and is an important part of understanding the virus.

The disease has been reported in various regions across the African continent, particularly in sub-Saharan Africa, as well as Saudi Arabia and Yemen. Heavy precipitation and an upsurge in mosquito populations are connected to the epidemiology of RVF. RVF outbreaks typically occur after periods of heavy rainfall when mosquito populations increase rapidly. These conditions favor transmission of the virus between mosquitoes and susceptible animal hosts like cattle, sheep, goats, camels, buffalo, and antelope species. Rodents such as rats and mice can also be infected. In addition to these natural reservoirs for the virus, human infections result from direct contact with animals that are infected or through bites from infected mosquitoes.

Notable Rift Valley Fever zoonotic disease (RFV) outbreaks*

• 1974 – 1976: South Africa: 220 cases
• 1977 – 1978: Egypt: 18,000 cases
• 1987 – 1988: Mauritania: 284 cases
• 1991: Madagascar: 994 cases
• 1997-1998: Kenya, Tanzania, Somalia: 8,000
• 1998: Mauritania: 400 cases
• 2000 – 2001: Saudi Arabia: 883 cases
• 2006 – 2007: Kenya: 684 cases
• 2006 – 2007: Tanzania: 309 cases
• 2007: Sudan: 747 cases
• 2008: South Africa: 367 cases
• 2008 – 2009: Madagascar: 418 cases
• 2010: South Africa: 221 cases
• 2016: Niger: 399 cases
• 2018: South Africa: 254
• 2019 – 2020: Sudan: 1,962 cases
• 2021: Madagascar: 109 cases
• 2022: Mauritania: 47 cases

*Note: These Rift Valley Fever zoonotic disease outbreaks include reported cases in both humans and animals. For a complete list of outbreaks and breakdown by humans and animals, visit GIDEON, a leading infectious diseases database.

Mosquito vectors and disease spread

The primary vectors responsible for transmitting RVF are mosquitoes belonging to the genera Aedes and Culex. Specifically, Aedes species are known to be involved in initiating outbreaks by transmitting the virus among animals, while Culex mosquitoes play a role in amplifying it within affected communities. Understanding this complex interplay between different mosquito vectors is crucial for predicting potential areas at risk for future outbreaks.

Influence on animal health and human infections

• Animal health: Infected livestock often suffer severe consequences, including high mortality rates among young lambs or abortions during pregnancy in ewes.
• Human infections: The virus can infect humans through direct contact with infected animals during animal births, during veterinary procedures, or by handling contaminated body fluids and tissues. However, indirect transmission is possible through mosquitoes and can also lead to severe disease in some cases.

Understanding the modes of transmission is crucial for implementing effective prevention measures. There are two main ways in which humans become infected with RVF: direct contact with blood or organs from slaughtered animals and indirect transmission through mosquito bites.

Direct contact

Humans can contract RVF by handling tissues, body fluids, or organs from animals infected with RVFV during slaughtering, veterinary procedures, or animal births. This mode of transmission puts individuals working in occupations such as farming, livestock trading, and veterinary medicine at higher risk for infection. It’s essential to follow proper handling practices when dealing with potentially infected animal materials to minimize the risk of exposure.

Indirect transmission

Rift Valley Fever zoonotic disease spreads among animals and between animals and humans via mosquito vectors like Culex mosquitoes, Aedes species, and other biting insects found across sub-Saharan Africa, eastern Africa, and East Africa regions on the African continent. When these mosquitoes bite an infected animal host – typically cattle, sheep, goats, camels, buffalo, antelope, rodents, rats, or mice – they acquire the virus. After incubating it within their bodies for some time, they transmit it while feeding on another susceptible host.

In addition to mosquito-borne transmission, outbreaks have been linked to heavy rainfall events, leading to increased populations of potential vectors and rapid disease spread. Preventing human infections requires concerted efforts in both controlling vector populations and reducing contact between people and animals that are infected.

Rift Valley fever (RVF) is a viral zoonosis caused by the RVF virus, which belongs to the genus Phlebovirus within the family Bunyaviridae, a group that includes yellow fever. The disease affects both wild and domesticated animals across sub-Saharan Africa, eastern Africa, and parts of the Arabian Peninsula. Although it can infect various species, young lambs and goats are particularly susceptible to severe disease. Pregnant sheep almost always abort if they contract RVF during their gestation period.

The transmission cycle of RVF involves mosquito vectors such as Aedes and Culex mosquitoes that become infected after feeding on viremic animals. Once infected, these flying insects can spread the virus to other creatures or people by biting them. The increased mosquito populations following periods of heavy rainfall contribute significantly to RVF outbreaks in affected regions.

• Mosquito Vectors: Mosquitoes from several genera serve as vectors for transmitting Rift Valley fever virus between animal hosts or from animals to humans. Some common vector species include those belonging to Aedes and Culex genera.
• Susceptible Animal Hosts: While many different animal species can be infected with Rift Valley fever virus, certain groups like cattle, sheep, goats, camels, buffalo, and antelope species are more prone than others due to factors such as age or pregnancy status.
• Zoonotic Transmission: Humans may become infected with Rift Valley fever either directly through contact with blood or organs from slaughtered animals or indirectly via bites from infected mosquitoes. This highlights the importance of understanding and controlling disease spread in both animal health and human populations.

Understanding the biology of RVF is crucial for implementing effective prevention measures, outbreak investigation, and control strategies to protect both animal health and human lives on the African continent.

The manifestations of Rift Valley Fever zoonotic disease depend on the intensity of infection. According to the World Health Organization (WHO), the incubation period varies from 2-6 days.

Human infections

In many cases, human infections are not associated with any noticeable symptoms. However, some individuals may develop more severe disease manifestations. Common symptoms include:

• Fever
• Muscle pain
• Joint pain
• Headache
• Vomiting and diarrhea (in some cases)

About 8-10% of infected individuals may experience more severe complications such as:

• Hemorrhagic fever: Bleeding disorders including nosebleeds, vomiting blood, or bleeding from other body sites
• Encephalitis: Swelling and inflammation of the brain causing confusion, seizures, or coma
• Retinitis: Inflammation in the retina leading to vision loss or blindness
• Death

Animal health

The impact of RVF on animal health varies among species; however, young lambs and goats are particularly susceptible, while pregnant sheep almost always abort if they contract the infection during the gestation period.

1. Livestock: Animals with RVFV infections often exhibit signs such as fever, weakness, nasal discharge, abortion, and sudden death.
2. Wildlife: The disease may cause significant mortality in certain wild animal populations, particularly antelope species.

In both human and animal cases, early detection and appropriate medical intervention on are crucial for minimizing the impact of RVF infection.

Early diagnosis of RVF in both humans and animals is crucial to prevent the spread of the disease and implement appropriate treatment measures. Several diagnostic techniques are available, each with its advantages and limitations.

Reverse Transcription Polymerase Chain Reaction (RT-PCR)

Reverse transcription polymerase chain reaction (RT-PCR) is a highly sensitive molecular technique used to detect the presence of RVF virus RNA in blood samples or tissue specimens. This method allows for rapid identification of active infections, even before symptoms appear.

Enzyme-linked Immunosorbent Assay (ELISA)

The ELISA technique is able to recognize antibodies generated by the body in reaction to a RVF infection. ELISA tests can identify both recent and past infections, making them useful for seroprevalence studies as well as outbreak investigations.

Immunofluorescence Assays

Immunofluorescence assays, such as indirect fluorescent antibody tests, involve staining fixed cells infected with RVF virus using fluorescein-labeled anti-RVF antibodies. These tests provide visual confirmation of viral antigens within infected cells under a fluorescencee microscope.

Serological Testing for Specific IgM and IgG Antibodies

Serological testing involves detecting specific immunoglobulin M (IgM) and immunoglobulin G (IgG) antibodies in blood samples. Recent IgM antibodies indicate a current infection, while past exposure to the virus is indicated by the presence of IgG antibodies.

No specific antiviral medication has been developed to treat Rift Valley fever in humans as of yet. Management of the disease primarily focuses on providing supportive care to alleviate symptoms and prevent complications. The mainstay of RVF treatment includes:

• Symptomatic management: This involves addressing the patient’s symptoms, such as fever, headache, muscle pain, and joint pain, with medications like acetaminophen or nonsteroidal anti-inflammatory drugs (NSAIDs).
• Fluid replacement therapy: Patients experiencing severe dehydration due to vomiting or diarrhea may require intravenous fluids to maintain electrolyte balance and hydration.
• Hospitalization: In cases where patients develop more severe manifestations of RVF, like hemorrhagic fever or encephalitis, hospitalization may be necessary for close monitoring and intensive care support.

In addition to these general measures, healthcare professionals should also educate patients about the importance of personal protective measures against mosquito bites during an outbreak. These include using insect repellent containing DEET or picaridin on exposed skin surfaces; wearing long-sleeved shirts and pants; sleeping under a bed net treated with permethrin; and eliminating standing water around their homes where mosquitoes can breed.

Vaccination remains one of the most effective strategies for controlling RVF outbreaks among animal populations. Currently, available vaccines include live-attenuated strains such as the MP-12 vaccine candidate, which has shown promising results in clinical trials but is not yet licensed for human use. Other experimental vaccines are being developed based on recombinant technology that utilizes viral proteins or virus-like particles. Until a safe and effective human vaccine becomes available, prevention measures and supportive care remain the primary means of managing RVF infections.

Preventing the spread of RVF requires a multifaceted approach, including proper handling practices during animal slaughter, personal protective equipment use in high-risk occupations, and vector control measures.

Proper Handling Practices During Animal Slaughter

One of the primary ways humans become infected with RVF is through direct contact with blood or organs from slaughtered animals. To minimize this risk, it’s essential to implement safe handling practices when conducting veterinary procedures or slaughtering animals for consumption. These include wearing gloves and other protective clothing while working with potentially infected animals or their tissues, properly disposing of waste materials like placenta after animal births, and ensuring cleanliness in abattoirs.

Vector Control Measures

• Mosquito control: Since RVF outbreaks are often linked to heavy rainfall events leading to increased mosquito populations, controlling these vectors plays an essential role in prevention efforts. This involves reducing breeding sites for mosquito vectors like Aedes and Culex mosquitoes by eliminating standing water, using insecticides, and implementing community-based interventions.
• Vaccination: Vaccines are available to protect livestock from RVF infection; however, there is currently no licensed vaccine for human use. To protect against transmission to people, it is important to ensure that susceptible animals are vaccinated widely.

In conclusion, preventing Rift Valley fever requires a combination of proper handling practices during animal slaughter, personal protective equipment use in high-risk occupations, and vector control measures. By implementing these strategies effectively across affected regions on the African continent and beyond, we can mitigate the impact of this devastating disease on both human health and animal welfare.

Can Rift Valley fever be transmitted from human to human?

Human-to-human transmission of RVF is rare. The primary mode of transmission is through infected mosquitoes or direct contact with infected animal blood or tissues. However, there have been isolated cases of human-to-human transmission via close contact with an infected person’s bodily fluids.

What does Rift Valley fever do to animals?

In animals, Rift Valley Fever zoonotic disease causes high mortality rates in young livestock and abortion in pregnant females. Infected animals may exhibit symptoms such as fever, weakness, loss of appetite, nasal discharge, and diarrhea. Severe outbreaks can lead to significant economic losses for farmers due to decreased productivity and trade restrictions.

Rift Valley Fever zoonotic disease was first identified in Kenya and has since spread to other African countries and beyond. It is primarily transmitted through mosquito vectors and direct contact with infected animals, with heavy rainfall and livestock movement playing a role in its epidemiology. Signs may be gentle, similar to the flu, or more severe; nevertheless, early detection through serological testing and RT-PCR assays can help with treatment.

Prevention strategies such as animal population surveillance and vector control efforts are crucial in managing the spread of Rift Valley Fever zoonotic disease. Healthcare professionals should stay up-to-date on guidelines for diagnosis and treatment from health organizations, as well as research articles about Rift Valley Fever’s history and epidemiology.

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Learn more about Rift Valley fever on the GIDEON platform.