Rift Valley Fever

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Key points

  • Rift Valley fever (RVF) is an important human and veterinary pathogen that causes significant illness and death.

  • The life cycle of RVF is complex and involves mosquitoes, livestock, climate, and humans.

  • RVF virus is transmitted from either mosquitoes or animals to humans, but is generally not transmitted from person to person.

  • There is a significant risk of emergence of RVF into new locations, which would affect human health and livestock industries.

  • There are no approved vaccines or therapeutics

Overview

One Health is a concept that recognizes the inextricable linkages between human health, animal health, and the environment (Fig. 1). Rift Valley fever (RVF) is a long-recognized veterinary disease of livestock in Africa. Infection with RVF virus (RVFV) causes a highly lethal illness in domesticated livestock (sheep, cattle, and goats) that consequently has dire economic impacts in affected regions. RVF has been and remains on the World Organization for Animal Health’s list of notifiable animal

Microbiology

RVFV is one of the most important members of the large and diverse Bunyaviridae family. RVFV belongs to the Phlebovirus genus, which also contains other viruses including Punta Toro, Sandfly fever, and severe fever with thrombocytopenia syndrome virus. The name phleobovirus is derived from the fact that most of the viruses in this genus are transmitted by phlebotomine sandflies. RVFV is a notable exception because it is transmitted primarily by mosquitoes. All bunyaviruses, including RVFV,

Epidemiology

The epidemiology of RVFV is complex and involves multiple players, including mosquitoes, wild animals, domesticated livestock, and humans (Fig. 2).

Biosafety and biodefense concerns

Of note, a significant number of accidental infections with RVFV have occurred among people performing diagnostic testing or those working with the virus in animals or the laboratory.39, 40, 41, 42, 43 At least 25 accidental infections occurred through 1949,39 with a total of 47 to date. Many of these infections were traced to aerosol (inhalational) exposure.39, 40 These laboratory-acquired infections led to early knowledge about the disease course in humans.

The United States, Canada, Japan,

Livestock

The clinical disease of RVF in domesticated animals is described in Table 3.2, 57, 58, 59 At all stages of gestation, infection of pregnant domesticated animals will result in near 100% death of the fetuses. Adult livestock are susceptible to peracute disease, which is defined as the occurrence of death before the development of any clinical signs. Adult livestock can also develop acute disease characterized by weakness, anorexia, diarrhea, bloody nasal discharge, and jaundice. The mortality

Diagnosis

In endemic regions, human illness soon follows in areas where there is concurrent RVF disease in animals, so monitoring of herds and efficient reporting is critical. Blood samples from acutely infected people can be tested for the presence of virus by either reverse transcriptase polymerase chain reaction, antigen-detection enzyme-linked immunosorbent assay, or isolation of live virus. After the cessation of viremia, immunoglobulin (Ig)M can be detected transiently. Recovered patients will have

Treatment and prevention

There are no specific, Food and Drug Administration-approved treatments for RVF. Treatment of symptoms such as fever and body aches can be done with standard over-the-counter medications. Care of hospitalized patients is supportive, including fluid replacement. Drugs that affect the liver, kidney, or coagulation should be avoided.

Prevention of animal and human outbreaks

The first step in the prevention of significant human disease is early detection of cases in animals through rigorous active surveillance and sentinel herd monitoring.96 Once infected animals and/or herds are located, further spread can be prevented by mosquito control, animal movement control, ban on livestock slaughtering, or at least use of preventative measures (gloves, masks, and gowns) when handling carcasses or aborted fetuses. Public awareness and education as to the signs, symptoms,

Potential for emergence

RVFV has spread throughout Africa, to the island of Madagascar, and into the Saudi Arabian peninsula. Most recently, endemic RVF was discovered in both Angola and Nigeria.98 Notably, human cases have not yet been recognized in these areas, potentially owing to focus on other diseases such as malaria, Yellow fever, and Dengue.

Concern over the further spread of RVF outside of Africa or the Saudi Arabian peninsula stems from the unexpected expansion of other arboviruses, namely West Nile,

Summary

RVF is a One Health disease that highlights the need to consider climate, veterinary health, and human behavior to prevent future outbreaks. Prevention of significant epizootics and epidemics is important in endemic areas owing to the severe economic impact. Also critical is prevention of spread to new areas.

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      Rift Valley fever virus (RVFV) was first identified in 1930 during an investigation into an outbreak among sheep on a farm in Kenya’s Rift Valley.71 RVFV belongs to the order of Bunyaviridae, and is endemic in several African countries, as well as in the Arabian Peninsula (Fig. 1).4,71 Outbreaks occur regularly, with an estimated 200,000 human infections during the largest recent outbreak (in Egypt 1977-1979).

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