Recent re-emergence of Rift Valley fever: epidemiology, clinical characteristics, transmission, symptoms, diagnosis, prevention, and treatment

Dear Editor,

Domestic animals like buffalo, camels, cattle, goats, and sheep can develop severe illness from the acute arthropod-borne viral disease known as Rift Valley fever (RVF), which is another significant zoonotic disease that can lead to serious illness in humans. In 2000, the illness was discovered for the first time outside of Africa on the Arabian Peninsula. This sparked worries that the Rift Valley fever virus (RVFV) would spread to other regions of Asia and Europe. Egypt and sub-Saharan Africa both have outbreaks. The severity of the illness in susceptible animals can vary, but symptoms such as fever, listlessness, anorexia, a disinclination to move, abortions, and high rates of morbidity and mortality in neonatal animals are common1. After a case of RVF was confirmed in a lab by PCR at the National Institute for Public Health Research on August 29, the Mauritania Ministry of Health alerted the WHO of an outbreak on August 30, 2022. A 25-year-old male animal breeder from Tintane moughataa (also known as district), Hodh El Gharbi wilaya, was the subject of the lawsuit (also known as region). He first showed up at a clinic on August 25 with the hemorrhagic syndrome (epistaxis) and acute thrombocytopenia. The next day, he was moved to a nearby hospital, where he passed away on August 29. Nine of Mauritania’s 15 wilayas have reported a total of 47 confirmed cases as of October 17, 2022, including 23 deaths (case fatality rate 49%), largely among those who breed animals. Men outnumber women among the 47 confirmed cases (sex ratio of male : female cases is 4.4 : 1). The cases range in age from 3 to 70 years, with a median age of 22 years. The hemorrhagic syndrome (petechiae, hematemesis, and gingivorrhagia) symptoms included severe thrombocytopenia and fever, and nearly all of the 23 deaths took place in hospitals2.

Since the 1950s, countries in East and Southern Africa have seen severe RVF outbreaks and endemic human disease. In the 1980s, there was an epidemiologic shift in several West African nations, which was thought to be related to climate change. It has been suggested that the cattle trade was responsible for the virus’s early 2000s geographic spread to Yemen and Saudi Arabia. In addition to those places, outbreaks have also occurred in the 21st century in Somalia, Kenya, Tanzania, Egypt, Madagascar, the Republic of South Africa, Niger, Namibia, Mauritania, Uganda, and most recently in Mayotte and Sudan in 2019. People who come into contact with sick animals, get bitten by mosquitoes, or both, such as farmers and herders, are risk factors. It has been observed that there is a male predominance with a male : female ratio of 3.5 : 1. Ocular manifestations affect 0.5–1.5% of the RVF patients, though visual symptoms affected 15% of the infected community during an outbreak in southwest Saudi Arabia in 20003. The incubation phase lasts somewhere between 2 and 5 days. The symptoms of basic human RVF and nonsymptomatic infections include an acute influenza-like illness with a transient fever, rigors, headache, agonizing muscle and joint pain, photophobia, and anorexia. Patients may occasionally experience epistaxis, nausea, vomiting, and a petechial rash. The illness lasts between 4 and 7 days, with a 2-week healing period. A hemorrhagic diathesis with hepatitis is a severe type of condition that is characterized by an initial febrile illness lasting 2–4 days, followed by jaundice and extensive hemorrhages in the mucosae and subcutaneous tissues. When a needle is inserted, bleeding might happen from the nose and gums. Melena-related hematemesis and diarrhea are possible. Within the next 3–6 days, patients typically pass away. After a protracted, sluggish convalescence, some people might recover. Retinitis, which typically develops bilaterally and manifests 1–3 weeks after the initial feverish illness, is the most common consequence. In 50% of cases, the center vision is permanently lost; permanent unilateral or bilateral blindness is also possible. The second febrile phase is when encephalitis can emerge. Patients experience confusion, hallucinations, dizziness, and choreiform movements, which can occasionally result in coma. Although the case fatality rate is often low, full recovery may take a while, and there have been reports of long-term neurological problems4. Blood, bodily fluids, or tissues of infected animals, primarily livestock, including cattle, sheep, goats, buffalo, and camels, are the usual routes by which people contract RVF. When caring for sick animals, during veterinary operations including supporting an animal during childbirth, during butchering or slaughter, or when consuming raw or undercooked animal products, direct contact with an animal may take place. Additionally, contaminated mosquito bites and, in rare cases, bites from other biting insects can cause RVF in humans. In laboratories, the RVFV infection has been brought on through airborne virus inhalation (known as aerosol transmission). When common infection control measures have been used, there has not been any evidence of transmission of RVF from one person to another or from health-care personnel to patients. The RVFV transmission cycle may resemble this: The eggs of female mosquitoes can transmit the virus to their progeny (vertical transmission). The virus can survive (remain infectious) in the eggs in dry conditions for a number of years. The infection risk for humans increases as a result of increased handling of infected animals during RVFV outbreaks in animals, most frequently livestock. The Aedes and Culex mosquitoes are the most frequent mosquito species that transmit RVFV, although other species can transmit as well. Rainfall in particular is a significant risk factor for environmental epidemics in both animals and people. Due to the fact that RVF is carried by mosquitoes, which are made more numerous by heavy precipitation, outbreaks of the disease are frequently associated with years of extremely high rainfall and flooding5.

RVFV is spread among ruminants through direct contact with the bodily fluids of infected animals and mosquito bites, primarily from members of the Aedes and Culex genera. Additionally, RVFV transmission by biological or mechanical means was successfully re-created in an experimental setting using additional hematophagous flies, but the field applicability of these transmission methods is yet unknown. Humans become infected primarily by direct contact with blood, contact with contaminated animal excrement, intake of raw milk, and in a small number of unusual instances, mosquito bites6. The RVFV typically causes an infection that is asymptomatic or a mild sickness with a fever and abnormalities of the liver. Fever, headache, widespread weakness, dizziness, weight loss, myalgia, and back pain are examples of simple infection symptoms. Additionally, some patients have photophobia, vomiting, and neck stiffness. Most people experience a spontaneous recovery within 2–7 days. A tiny minority of patients experience complications such hemorrhagic fever, meningoencephalitis, or eye illness. Typically, hemorrhagic fever appears 2–4 days following the onset of symptoms. Jaundice, hematemesis, melena, a purpuric rash, petechiae, and gum bleeding are possible signs. Frank hemorrhages, shock, and death can result from hemorrhagic fever. Meningoencephalitis and eye illnesses are often diagnosed 1–3 weeks following the onset of symptoms. The ocular type is distinguished by retinal lesions and may cause a temporary or permanent loss of vision. Meningoencephalitis or eye illnesses rarely result in death7.

Molecular diagnostics, such as the DIVA test, are available to detect RVFV (gel-based and RT PCR). There are serological tests available to identify early RVF infection from past RVF infection in domestic ruminants and to detect RVF antibodies. The diagnostic capabilities of the laboratories in the EU, as well as those from Algeria, Mauritania, Morocco, Tunisia, Mali, and Senegal, have been evaluated, with the level of performance there considered adequate. The majority of the other Mediterranean nations have RVF diagnostic procedures in place; nonetheless, interlaboratory trials should be encouraged to assess how well they work8. Since there is no specific treatment for RVF, symptomatic and supportive care is typically advised. Controlling animal movements, taking precautions at slaughterhouses to prevent or reduce exposure to the disease, and managing mosquito populations can all help prevent the spread of disease. However, during epidemics, vector control and sanitary prophylaxis may only have a marginal impact. A live-attenuated mutant vaccination, an inactivated virus vaccine (Smithburn strain), or an attenuated virus vaccine may be administered to the animals. The human vaccination is still being developed. In order to discover new occurrences of RVF and provide early warnings to veterinary and human public health authorities, active surveillance is necessary9.

The majority of RVF cases are mild, so little treatment is needed. Supportive therapy, which focuses on treating the symptoms and making the patient feel more comfortable, is used to treat more severe forms of this disease. For instance, ibuprofen or aspirin can be administered to RVF patients who are experiencing fever and body aches. There is a vaccine available that can shield someone from contracting RVF. This vaccine, however, has not yet received approval for widespread use and has only been tested on staff members of veterinary practices who work in close proximity to potential recipients. Research and testing on this vaccination and other potential vaccines are ongoing10. However, investigations on animals have shown that the antiviral drug ribavirin is effective. In most instances, only symptomatic treatment will have positive results. Trials for the RVF vaccine are still ongoing11. So, the purpose of this study was to detail the outbreak, epidemiology, clinical features, transmission, signs, symptoms, diagnostic tests, prevention, and medication of RVF.

Ethics approval

Not applicable.

Sources of funding

None.

Author’s contributions

Md. Mominur Rahman: Conceptualization, writing – original draft preparation and supervision. Md. Rezaul Islam, Puja Sutro Dhar: writing, editing. All authors have reviewed and approved the final version of the manuscript prior to submission.

Conflict of interest

The authors declare no conflict of interest, financial or otherwise.

Data availability statement

All the data used to support the findings of this study are included in the article.