Rift Valley Fever
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Rift Valley Fever (RVF) is a viral disease that affects mainly animals and occasionally humans. The virus is a member of the Phlebovirus genus, one of the five genera in the family Bunyaviridae. The disease is frequently reported following heavy rainfall and floods. RVF is mainly transmitted from animals (sheep, cattle, goats, camels) to humans through close contact with infected animals (such as handling meat and body fluids and consumption of raw milk). During established RVF outbreaks in animals, humans can also get infected through bites of infected mosquitoes and other biting insects.
The incubation period of RVF varies from 2 to 6 days. These symptoms usually last from 4 to 7 days. Most of the infected people recover on their own. However, a small proportion gets complications such as vomiting blood, nose bleeding and passing bloody stool. Rift Valley fever is difficult to distinguish from other viral haemorrhagic fevers as well as many other diseases that cause fever, including malaria, shigellosis, typhoid fever, and yellow fever.
Case Definitions
Suspected case: Early Disease: Acute febrile illness (axillary temperature >37.5 ºC or oral temperature of >38.0ºC) of more than 48 hours’ duration that does not respond to antibiotic or antimalarial therapy, and is associated with:
- Direct contact with sick or dead animal or its products AND/OR
- Recent travel (during last week) to, or living in an area where, after heavy rains, livestock die or abort, and where RVF virus activity is suspected/confirmed AND/ OR
- Abrupt onset of any 1 or more of the following: exhaustion, backache, muscle pains, headache (often severe), discomfort when exposed to light, and nausea/vomiting AND/ OR:
- Nausea/vomiting, diarrhoea OR abdominal pain with 1 or more of the following:
- Severe pallor (or Hb < 8 gm/dL)
- Low platelets (thrombocytopenia) as evidence by presence of small skin and mucous membrane haemorrhages (petechiae) (or platelet count < 100x109/d
- Evidence of kidney failure (edema, reduced urine output) (or creatinine > 150mol/L) AND/OR
- Evidence of bleeding into skin, bleeding from puncture wounds, from mucous membranes or nose, from gastrointestinal tract and unnatural bleeding from vagina AND/OR
- Clinical jaundice (3-fold increase above normal of transaminases)
Late stages of diseases or complications: (2-3 weeks after onset)
- Patients who have experienced, in the preceding month a flu-like illness, with clinical criteria, who additionally develop the following:
- CNS manifestations which resemble meningo-encephalitis AND/OR:
- Unexplained visual loss OR
- Unexplained death following sudden onset of acute flu-like illness with haemorrhage, meningo-ecephalitis, or visual loss during the preceding month.
Confirmed case:
Any patient who, after clinical screening, is positive for anti-RVF IgM ELISA antibodies (typically appear from fourth to sixth day after onset of symptoms) or tests positive on reverse transcriptase polymerase chain reaction (RT-PCR).
Transmission to human is mainly through direct or indirect contact with blood or organs of infected animals. The virus can be transmitted to human through:
- Handling of animal tissue during slaughtering or butchering, assisting with animal births, conducting veterinary procedures
- Inoculation e.g. via wound from infected knife or through contact with broken skin or through inhalation of aerosols produced during the slaughter of an infected animals
- Infected mosquito
Human become viraemic; capable of infecting mosquitoes shortly before onset of fever and for the first 3–5 days of illness. Once infected, mosquitoes remain so for life.
Clinical Diagnostic Criteria
- Acute febrile illness that does not respond to antibiotic or antimalarial therapy
- Exhaustion, backache, muscle pains, headache (often severe)
- Photophobia
- Nausea/vomiting
- Evidence of bleeding into skin, bleeding from puncture wounds, from mucous membranes or nose, from gastrointestinal tract and unnatural bleeding from vagina
- Clinical jaundice (3-fold increase above normal of transaminases)
Clinical diagnosis is difficult, because RVF symptoms can be mild and non-specific, especially early in the course of the disease.
Laboratory InvestigationsDefinitive diagnosis of RVF involves laboratory testing of blood (during illness) or other tissue samples (postmortem tissue).
The virus detection in the blood then virus isolation in cell culture
- Molecular techniques (reverse transcriptase polymerase chain reaction or RT-PCR)
- Antibody testing using Enzyme-Linked ImmunoAssay (ELISA) confirms infection with RVFV
- IgM antibodies reflect a recent infection and IgG antibodies persist for several years (detection of anti-RVF IgM suggests an ongoing transmission of RVFV in humans during inter-epidemic periods)
- FBC
- Low Hb [Hb<8gm/dL - Severe pallor
- Low platelet < 100 x109 /Dl (Thrombocytopenia – small skin and mucous membrane hemorrhages (Petechiae))
- Serum Creatinine
Note: Acute RVF can be diagnosed using several different methods
- Serological tests such as ELISA may confirm the presence of specific IgM antibodies to the virus. The virus itself may be detected in blood during the early phase of illness or in post-mortem tissue using a variety of techniques including antigen detection tests by ELISA, RT-PCR, virus propagation (in cell cultures), immunohistochemistry in formalin-fixed tissues
- ELISA IgG can be used for retrospective diagnostic
Management
Management of RVF in humans is mainly supportive as there is no definitive treatment for RVF. Early detection and management of the disease is important. Human control of RVF is through control of the disease in animals through a sustained vaccination program and limiting human-animal contact. Use of insecticide treated nets and mosquito repellents can also reduce infections in human. In addition to human suffering and death, RVF has far reaching economic implications to the livestock industry. In outbreak settings, the disease manifestation includes non-haemorrhagic febrile syndromes, and laboratory testing should be considered among persons with milder symptoms suggestive of viral illness.
Prevention
People living in or visiting areas with RVF shall be protected from the RVF infection with these steps:
- Protect people from contact with blood, body fluids, or tissues of infected animals (use PPEs like gloves, boots, long sleeves, and a face shield).
- Protect people from unsafe animal products. All animal products (including meat, milk, and blood) should be thoroughly cooked before eating or drinking.
- Protect people from mosquitoes and other bloodsucking insects. Use insect repellents and bed nets, and wear long sleeved shirts and long pants to cover exposed skin.
No vaccines are currently available for vaccination in people at risk of RVF infection.
Public Health Control Measures
- Mobilize the community for early detection and care.
- Conduct community education about the confirmed case, how the disease is transmitted, and how to prevent contact with tissues of infected animals and avoid mosquito bites.
- Provide information about prevention in the home and when to seek care.
- Provide supportive treatment to all cases identified
- Collaborate with the animal health specialists to search and document cases among animals as well.