Last Updated: 25 July, 2010
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INTERIM REPORT ON THE RIFT VALLEY FEVER (RVF) OUTBREAK IN SOUTH AFRICA

Data and information last updated: 25 July 2010

Report issued by: The Outbreak Response Unit, Special Pathogens Unit, and South African Field Epidemiology and Laboratory Training Programme (SAFELTP), National Institute for Communicable Diseases (NICD) of the National Health Laboratory Service (NHLS). In collaboration with the South African Department of Health and Department of Agriculture, Forestry and Fisheries.

Case summary:

Investigations to obtain a detailed history on all confirmed cases are ongoing, and all data presented here is thus preliminary and subject to change. We are able to provide the following information based on data collected to date. As of 21 July 2010, we have confirmed a total of 229 human cases and 26 deaths (Table 1). Cases range in age from 1 – 86 years (median 43 years), and the majority (86%, 196/229) are male.

Table 1: Number of laboratory-confirmed RVF cases and deaths by province, South Africa
Province (place exposed)
Cases
Deaths
Eastern Cape
17
1
Free State
123
11
Gauteng
0
0
KwaZulu-Natal
0
0
Limpopo
0
0
Mpumalanga
0
0
Northern Cape
75
11
North West
9
2
Western Cape
4
1
Unknown
1
-
South Africa Total
229
26


Occupation and exposure

Of the 229 confirmed cases, data on occupation is available for 214 cases (93%). Of these, the majority (81%, 174/214) work within occupations where direct contact with animals frequently occurs (Table 2).

Table 2: Number of laboratory-confirmed RVF cases by occupation group, South Africa

Occupation

No. (%)

Farmer or farm worker

130 (61)

Animal health worker †

16 (7)

Abattoir worker, meat inspector or hunter

28 (13)

Farm resident (non farm-worker)

3 (1)

Non-animal related occupation

37 (17)

Total with known occupation

213 (100)

† Includes veterinarians, veterinary assistants/nurses, animal health technicians.



Further history regarding exposure has been obtained for 87% (199/229) of the total cases to date. Amongst these cases, 94% (187/199) report a history of direct contact with RVF-infected ruminants prior to onset of symptoms, 3.5% (7/199) report exposure to mosquitoes in the absence of direct animal/animal tissue or unpasteurised milk exposure, and 2.5% (5/199) re¬port drinking unpasteurised milk but no direct con¬tact with infected animals.

Progress of the outbreak

There has been one additional laboratory confirmed RVF case (positive serology) since our last update. The patient is a farm worker from Northern Cape Province who handled and slaughtered sheep. On 6 July 2010, he developed an illness in keeping with acute RVF infection. This is the most recent human case confirmed to date and highlights the possibility of continued transmission in limited areas. Historically, the onset of cold weather in RVF-affected areas results in die-off of the mosquito vectors and often heralds the end of RVF outbreaks in animals and humans. There remains a need for continued vigilance amongst all healthcare workers. Clinicians should continue to suspect RVF in patients meeting the case definition and submit specimens to the NICD for laboratory testing. Additionally, clinicians should bear in mind that certain RVF-complications often manifest a few weeks after the acute infection; meningoencephalitis may present up to 4 weeks later, and ocular complications (notably retinitis) may present weeks to months later. In such cases, the acute infection may have been extremely mild and not have been diagnosed initially.

(A)
(B)
Figure 1: Epidemic curve illustrating the number of laboratory-confirmed RVF cases by epidemiological week of illness onset, by (A) laboratory tests and (B) province, South Africa, updated 21 July 2010 (N=298 cases, of which date of onset is available for 87% (n=200), and an additional 3% (n=7) of cases were asymptomatic).


HEALTH WORKERS GUIDELINES
ON
RIFT VALLEY FEVER (RVF)


Download the Guidelines here in pdf format (use right-click, Save as...).
Download the RVF Poster here in pdf format (use right-click, Save as...).

Content


  1. What is Rift Valley Fever?
  2. Has South Africa been affected in the past?
  3. How is it transmitted to humans?
  4. When should RVF be suspected? Case definition and criteria for laboratory testing
  5. What are the clinical features in humans?
  6. How is it diagnosed in the laboratory?
  7. Procedure following detection of a suspect case
    • Step 1: Notify the case
    • Step 2: Collect specimens for laboratory diagnosis
  8. How is it treated? Is there a vaccine?
  9. Infection control in healthcare settings
  10. How can RVF be prevented?
  11. How are outbreaks controlled?
  12. Where can I get more information?


Introduction


There is currently an ongoing outbreak of RVF affecting sheep, goat and cattle farms within Free State (FSP), Northern Cape (NCP), Eastern Cape (ECP), Western Cape (WCP), North West (NWP), Gauteng (GP) and North West (NWP) Provinces.

As of 9 April 2010, the NICD has confirmed a total of 111 human cases (81 cases from FSP, 22 cases from NCP, 7 cases from ECP and 1 case from NWP), including nine fatalities. The majority of cases report direct contact with RVF-infected livestock through occupational exposure, including: farmers and farm workers, animal health workers, abattoir workers and meat inspectors. Outbreak investigations by the Department of Agriculture, Forestry and Fisheries and Department of Health are ongoing, and are being supported by the South African Field Epidemiology and Training Programme (SA-FELTP) and NICD.

Disclaimer


This material is intended for use by healthcare professionals. While the greatest care has been taken in the development of the document, the National Department of Health and the National Institute for Communicable Diseases do not accept responsibility for any errors or omissions. All healthcare professionals should exercise their own professional judgement in confirming and interpreting the findings presented in the guidelines.

1. What is Rift Valley Fever?


Rift Valley Fever (RVF) is a viral zoonosis that can cause severe disease in a low proportion of infected humans. The virus is from the family Bunyaviridae (genus Phlebovirus) and causes outbreaks of abortions and deaths of young livestock (predominantly sheep, goats and cattle). Humans become infected from contact with infected tissues of livestock, and less frequently from mosquito bites. The mosquitoes which transmit the virus (Aedes and Culex mosquitoes) are present in South Africa; however, these species generally prefer to feed on livestock outdoors at night. The disease occurs throughout Africa and Middle East Asia when exceptionally heavy rains favour the breeding of the mosquito vectors.

2. Has South Africa been affected in the past?


Yes. The last major outbreak of RVF on the interior plateau of South Africa occurred in 1974-76 during prolonged heavy rains, causing 10,000 to 20,000 human cases. Since then, sporadic outbreaks and human infections have been documented within KwaZulu-Natal, the Kruger National Park, Limpopo, Gauteng, North West, and Northern Cape Provinces.

3. How is it transmitted to humans?
  • Direct or indirect contact with the blood or tissues of infected animals, including:
    • handling of animal tissue during slaughtering or butchering,
    • assisting with animal births
    • conducting veterinary procedures
    • disposal of carcasses or foetuses
  • Uncommon modes of transmission include:
    • inoculation, for example via a wound from an infected knife or needle-stick injuries or contact with broken skin
    • inhalation of aerosols produced during the slaughter of infected animals
    • bites of infected mosquitoes (most commonly Aedes)
  • Although very rare, there is evidence that humans may also become infected with RVFV by ingesting unpasteurised or uncooked milk of infected animals.
  • No human-to-human transmission has ever been documented.
Occupational groups such as herders, farmers, slaughterhouse workers and veterinarians are at higher risk of infection.

4. When should RVF be suspected? Case definition and criteria for laboratory testing


Any person reporting recent close contact with livestock in or from suspected RVF-affected areas, presenting with:
  • Influenza-like illness (which may include fever, myalgia, arthralgia or headache), OR
  • Fever and features of: encephalitis, haemorrhage, hepatitis and/or ocular pathology (retinitis).
**Precautions – other causes for these symptoms must be excluded where appropriate, including malaria, Crimean Congo Haemorrhagic Fever (CCHF) and Tick-Bite Fever. Obtaining a thorough history including other signs and symptoms, recent travel, insect (e.g. tick) exposures, contact with livestock, etc. will assist clinicians in narrowing the differential diagnosis.

5. What are the clinical features in humans?


Typically, illness is asymptomatic or mild in the vast majority of infected persons. Severe disease occurs in <1% of infected persons.

Mild illness
  • The incubation period (interval from infection to onset of symptoms) for RVF varies from two to six days.
  • Clinically, it presents as a fever with flu-like symptoms (including myalgia, arthralgia or headache)
  • Some patients may also develop neck stiffness, sensitivity to light (photophobia), pain behind the eyes, loss of appetite and vomiting; in such patients the clinical presentation may be mistaken for meningitis.
  • Symptoms of RVF usually last from four to seven days, after which time the immune response becomes detectable with the appearance of antibodies and the virus gradually disappears from the blood.
Severe illness

A small percentage of patients develop a much more severe form of the disease, but the overall mortality rate is <1%.

Complications include ocular (retinal) disease (0.5-2% of patients), meningoencephalitis (<1%), hepatitis, or haemorrhagic fever (<1%). The mortality rate of patients developing the haemorrhagic form of the disease is high (50%).
  • Ocular disease (retinitis): Onset of retinitis is usually one to three weeks after appearance of the first symptoms, and usually presents as blurred or decreased vision. It may resolve within 10 – 12 weeks with no sequelae. If lesions occur in the macula, ±50% of patients will experience a permanent loss of vision. Death in patients with only the ocular form of the disease is uncommon.
  • Meningoencephalitis: The onset of meningoencephalitis usually occurs one to four weeks after the first symptoms of RVF appear. Clinical features may include: intense headache, loss of memory, hallucinations, confusion, disorientation, vertigo, convulsions, lethargy and coma. Neurological complications can appear later (> 60 days). Although the mortality rate in patients who experience only this form of the disease is low, residual neurological deficit, which may be severe, is common.
  • Hepatitis: This is characterised by markedly raised transaminase enzymes (ALT and AST), and may occur together with other complications (e.g. haemorrhage or meningoencephalitis).
  • Haemorrhagic fever: Manifestations appear two to four days after the initial onset of illness. Usually, evidence of severe liver impairment (such as jaundice, or elevated liver enzyme levels) is present, followed by haemorrhage. This may present as haematemesis (vomiting blood), melaena (passing blood in the faeces), a petechial /purpuric rash or ecchymoses, bleeding from the nose or gums, menorrhagia, and bleeding from venepuncture sites.

6. How is it diagnosed in the laboratory?


The virus may be detected in blood during the early phase of illness or in post-mortem tissue by RT-PCR or isolation in cell cultures or mice. Enzyme-linked immunoassay (ELISA) may confirm the presence of specific IgM and/or IgG antibodies to the virus. These tests are performed by the Special Pathogens Unit, NICD.

7. Procedure following detection of a suspect case
Step 1: Notify the case
  • RVF is a notifiable medical condition and should be notified to your local Department of Health telephonically.
Step 2: Collect specimens for laboratory diagnosis

  • All suspected cases of RVF should have both a clotted blood (red/yellow top tube) and EDTA blood (purple top tube) specimens taken for viral detection and antibody.
  • The specimens should be packaged in accordance with the guidelines for the transport of dangerous biological goods (triple packaging using absorbent material) and transported directly to:
    The Special Pathogens Unit
    National Institute for Communicable Diseases (NICD)
    No. 1 Modderfontein Rd
    Sandringham, 2131
  • The specimen/s should be accompanied by the RVF specimen submission form or via the NICD website.
  • Samples should be kept cold during transport.
Should you require any clinical advice, or identify a patient with severe illness, please call the NICD Hotline 082-883-9920.

8. How is it treated? Is there a vaccine?
  • No specific treatment is available for RVF; management is aimed at general supportive therapy.
  • Ribavirin is not recommended.
  • Standard infection control precautions should be followed; patients do not require isolation or barrier nursing. Human-to-human transmission has not been demonstrated (see section on infection control).
  • Continual follow-up of patients for a 1 month period after symptoms resolve is necessary to monitor the possible development of retinal lesions.
  • There are no human RVF vaccines registered in South Africa for use by the general public.

9. Infection control in healthcare settings
  • Although no human-to-human transmission of RVF has been demonstrated, there is still a theoretical risk of transmission from infected patients to healthcare workers through contact with infected blood or tissues.
  • Healthcare workers caring for patients with suspected or confirmed RVF should implement “Standard Precautions”.
  • “Standard Precautions” define the work practices that are required to ensure a basic level of infection control, and are recommended in the care and treatment of all patients regardless of their perceived or confirmed infectious status. They cover the handling of blood (including dried blood), all other body fluids, secretions and excretions (excluding sweat), regardless of whether they contain visible blood, and contact with non-intact skin and mucous membranes.

10. How can RVF be prevented?


Public health education and risk reduction plays a vital role in preventing cases. Messages to the community, especially within affected areas should focus on:
  • Avoiding high-risk animal husbandry procedures and slaughtering practices through use of gloves and other protective clothing, especially when handling sick animals.
  • Avoiding the unsafe consumption of fresh blood, raw milk or animal tissue. In epizootic regions, all animal products (blood, meat and milk) should be thoroughly cooked before eating. Slaughtering of animals for consumption should be discouraged during outbreaks.
  • Personal and community protection against mosquito bites through the use of insect repellents (containing 30-50% DEET), insecticide-treated bed nets, and wearing of light-coloured clothing.

11. How are outbreaks controlled?


Prevention of RVF outbreaks primarily relies on the prevention of infection in livestock through vaccination and vector control. Farmers and veterinarians may refer to the Veterinary Control Guidelines. A veterinary (animal) vaccine is available in South Africa. Other ways in which to mitigate the spread of RVF involve control of the vector and protection against their bites. Larviciding measures at mosquito breeding sites are the most effective form of vector control if breeding sites can be clearly identified and are limited in size and extent. During periods of flooding, however, the number and extent of breeding sites is usually too high for larviciding measures to be feasible.

12. Where can I get more information?

Report issued by:
The Outbreak Response Unit, Special Pathogens Unit, and South African Field Epidemiology and Laboratory Training Programme (SAFELTP), National Institute for Communicable Diseases (NICD) of the National Health Laboratory Service (NHLS). In collaboration with the South African Department of Health and Department of Agriculture, Forestry and Fisheries.