RIFT VALLEY FEVER
RIFT VALLEY FEVER
Rift Valley Fever (RVF) is a viral zoonosis that primarily affects animals but also has the capacity to infect humans. Infection can cause severe disease in both animals and humans, leading to high rates of disease and death. The disease also results in significant economic losses due to death and abortion among RVF-infected livestock.
RVF virus is a member of the Phlebovirus genus, one of the five genera in the family Bunyaviridae. The virus was first identified in 1931 during an investigation into an epidemic among sheep on a farm in the Rift Valley of Kenya. Since then, outbreaks have been reported in sub-Saharan and North Africa. In 1997-98, a major outbreak occurred in Kenya, Somalia and Tanzania and in September 2000, RVF cases were confirmed in Saudi Arabia and Yemen, marking the first reported occurrence of the disease outside the African continent and raising concerns that it could extend to other parts of Asia and Europe.
TRANSMISSION TO HUMANS
* The vast majority of human infections result from direct or indirect contact with the blood or organs of infected animals. The virus can be transmitted to humans through the handling of animal tissue during slaughtering or butchering, assisting with animal births, conducting veterinary procedures, or from the disposal of carcasses or fetuses. Certain occupational groups such as herders, farmers, slaughterhouse workers and veterinarians are therefore at higher risk of infection. The virus infects humans through inoculation, for example via a wound from an infected knife or through contact with broken skin, or through inhalation of aerosols produced during the slaughter of infected animals. The aerosol mode of transmission has also led to infection in laboratory workers.
* There is some evidence that humans may also become infected with RVF by ingesting the unpasteurized or uncooked milk of infected animals.
* Human infections have also resulted from the bites of infected mosquitoes, most commonly the Aedes mosquito.
* Transmission of RVF virus by hematophagous (blood-feeding) flies is also possible.
* To date, no human-to-human transmission of RVF has been documented, and no transmission of RVF to health care workers has been reported when standard infection control precautions have been put in place.
* There has been no evidence of outbreaks of RVF in urban areas.
CLINICAL FEATURES IN HUMANS
Mild form of RVF in humans
* The incubation period (interval from infection to onset of symptoms) for RVF varies from two to six days.
* Those infected either experience no detectable symptoms or develop a mild form of the disease characterized by a feverish syndrome with sudden onset of flu-like fever, muscle pain, joint pain and headache.
* Some patients develop neck stiffness, sensitivity to light, loss of appetite and vomiting; in these patients the disease, in its early stages, may be mistaken for meningitis.
* The 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 form of RVF in humans
* While most human cases are relatively mild, a small percentage of patients develop a much more severe form of the disease. This usually appears as one or more of three distinct syndromes: ocular (eye) disease (0.5-2% of patients), meningoencephalitis (less than 1%) or haemorrhagic fever (less than 1%).
o Ocular form: In this form of the disease, the usual symptoms associated with the mild form of the disease are accompanied by retinal lesions. The onset of the lesions in the eyes is usually one to three weeks after appearance of the first symptoms. Patients usually report blurred or decreased vision. The disease may resolve itself with no lasting effects within 10 to 12 weeks. However, when the 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.
o Meningoencephalitis form: The onset of the meningoencephalitis form of the disease usually occurs one to four weeks after the first symptoms of RVF appear. Clinical features include intense headache, loss of memory, hallucinations, confusion, disorientation, vertigo, convulsions, lethargy and coma. Neurological complications can appear later (> 60 days). The death rate in patients who experience only this form of the disease is low, although residual neurological deficit, which may be severe, is common.
o Haemorrhagic fever form: The symptoms of this form of the disease appear two to four days after the onset of illness, and begin with evidence of severe liver impairment, such as jaundice. Subsequently signs of haemorrhage then appear such as vomiting blood, passing blood in the faeces, a purpuric rash or ecchymoses (caused by bleeding in the skin), bleeding from the nose or gums, menorrhagia and bleeding from venepuncture sites. The case-fatality ratio for patients developing the haemorrhagic form of the disease is high at approximately 50%. Death usually occurs three to six days after the onset of symptoms. The virus may be detectable in the blood for up to 10 days, in patients with the hemorrhagic icterus form of RVF.
The total case fatality rate has varied widely between different epidemics but, overall, has been less than 1% in those documented. Most fatalities occur in patients who develop the haemorrhagic icterus form.
DIAGNOSIS
* Acute RVF can be diagnosed using several different methods. Serological tests such as enzyme-linked immunoassay (the “ELISA” or “EIA” methods) 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 virus propagation (in cell cultures or inoculated animals), antigen detection tests and RT-PCR.
TREATMENT AND VACCINE
* As most human cases of RVF are relatively mild and of short duration, no specific treatment is required for these patients. For the more severe cases, the predominant treatment is general supportive therapy.
* An inactivated vaccine has been developed for human use. However, this vaccine is not licensed and is not commercially available. It has been used experimentally to protect veterinary and laboratory personnel at high risk of exposure to RVF. Other candidate vaccines are under investigation.
RVF VIRUS IN ANIMAL HOSTS
* RVF is able to infect many species of animals causing severe disease in domesticated animals including cattle, sheep, camels and goats. Sheep appear to be more susceptible than cattle or camels.
* Age has also been shown to be a significant factor in the animal’s susceptibility to the severe form of the disease: over 90% of lambs infected with RVF die, whereas mortality among adult sheep can be as low as 10%.
* The rate of abortion among pregnant infected ewes is almost 100%. An outbreak of RVF in animals frequently manifests itself as a wave of unexplained abortions among livestock and may signal the start of an epidemic.
RVF VECTORS
* Several different species of mosquito are able to act as vectors for transmission of the RVF virus. The dominant vector species varies between different regions and different species can play different roles in sustaining the transmission of the virus.
* Among animals, the RVF virus is spread primarily by the bite of infected mosquitoes, mainly the Aedes species, which can acquire the virus from feeding on infected animals. The female mosquito is also capable of transmitting the virus directly to her offspring via eggs leading to new generations of infected mosquitoes hatching from eggs. This accounts for the continued presence of the RVF virus in enzootic foci and provides the virus with a sustainable mechanism of existence as the eggs of these mosquitoes can survive for several years in dry conditions. During periods of heavy rainfall, larval habitats frequently become flooded enabling the eggs to hatch and the mosquito population to rapidly increase, spreading the virus to the animals on which they feed.
* There is also a potential for epizootics and associated human epidemics to spread to areas that were previously unaffected. This has occurred when infected animals have introduced the virus into areas where vectors were present and is a particular concern. When uninfected Aedes and other species of mosquitoes feed on infected animals, a small outbreak can quickly be amplified through the transmission of the virus to other animals on which they subsequently feed.
PREVENTION AND CONTROL
Controlling RVF in animals
* Outbreaks of RVF in animals can be prevented by a sustained programme of animal vaccination. Both modified live attenuated virus and inactivated virus vaccines have been developed for veterinary use. Only one dose of the live vaccine is required to provide long-term immunity but the vaccine that is currently in use may result in spontaneous abortion if given to pregnant animals. The inactivated virus vaccine does not have this side effect, but multiple doses are required in order to provide protection which may prove problematic in endemic areas.
* Animal immunization must be implemented prior to an outbreak if an epizootic is to be prevented. Once an outbreak has occurred animal vaccination should NOT be implemented because there is a high risk of intensifying the outbreak. During mass animal vaccination campaigns, animal health workers may, inadvertently, transmit the virus through the use of multi-dose vials and the re-use of needles and syringes. If some of the animals in the herd are already infected and viraemic (although not yet displaying obvious signs of illness), the virus will be transmitted among the herd, and the outbreak will be amplified.
* Restricting or banning the movement of livestock may be effective in slowing the expansion of the virus from infected to uninfected areas.
* As outbreaks of RVF in animals precede human cases, the establishment of an active animal health surveillance system to detect new cases is essential in providing early warning for veterinary and human public health authorities.
Public health education and risk reduction
* During an outbreak of RVF, close contact with animals, particularly with their body fluids, either directly or via aerosols, has been identified as the most significant risk factor for RVF virus infection. In the absence of specific treatment and an effective human vaccine, raising awareness of the risk factors of RVF infection as well as the protective measures individuals can take to prevent mosquito bites, is the only way to reduce human infection and deaths.
* Public health messages for risk reduction should focus on:
o reducing the risk of animal-to-human transmission as a result of unsafe animal husbandry and slaughtering practices. Gloves and other appropriate protective clothing should be worn and care taken when handling sick animals or their tissues or when slaughtering animals.
o reducing the risk of animal-to-human transmission arising from the unsafe consumption of fresh blood, raw milk or animal tissue. In the epizootic regions, all animal products (blood, meat and milk) should be thoroughly cooked before eating.
o the importance of personal and community protection against mosquito bites through the use of impregnated mosquito nets, personal insect repellent if available, by wearing light coloured clothing (long-sleeved shirts and trousers) and by avoiding outdoor activity at peak biting times of the vector species.
Infection control in health care settings
* Although no human-to-human transmission of RVF has been demonstrated, there is still a theoretical risk of transmission of the virus from infected patients to health care workers through contact with infected blood or tissues. Health care workers caring for patients with suspected or confirmed RVF should implement Standard Precautions when handling specimens from patients.
* Standard Precautions define the work practices that are required to ensure a basic level of infection control. Standard Precautions 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.
* Laboratory workers are also at risk. Samples taken from suspected human and animal cases of RVF for diagnosis should be handled by trained staff and processed in suitably equipped laboratories.
Vector control
* The most single factor in controling the vector is to know their life cycle and device best ways of control. Where Immunization is strongly recomended.
* Other ways in which to control 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.
RVF FORESCASTING AND CLIMATIC MODELS
Forecasting can predict climatic conditions that are frequently associated with an increased risk of outbreaks, and may improve disease control. In Africa, Saudi Arabia and Yemen RVF outbreaks are closely associated with periods of above-average rainfall. The response of vegetation to increased levels of rainfall can be easily measured and monitored by Remote Sensing Satellite Imagery. In addition RVF outbreaks in East Africa are closely associated with the heavy rainfall that occurs during the warm phase of the El Niño/Southern Oscillation (ENSO) phenomenon.
These findings have enabled the successful development of forecasting models and early warning systems for RVF using satellite images and weather/climate forecasting data. Early warning systems, such as these, could be used to detect animal cases at an early stage of an outbreak enabling authorities to implement measures to avert impending epidemics.
Within the framework of the new International Health Regulations (2005), the forecasting and early detection of RVF outbreaks, together with a comprehensive assessment of the risk of diffusion to new areas, are essential to enable effective and timely control measures to be implemented.
STANDARD PRECAUTIONS
Epidemic and pandemic aleart and response.
Health policy guidelines:
Promote a safety climate.
� Develop policies which facilitate the implementation
of infection control measures.
Hand hygiene
� Perform hand hygiene by means of hand rubbing
or hand washing (see detailed indications in
Table).
� Perform hand washing with soap and water
if hands are visibly soiled, or exposure to
spore-forming organisms is proven or strongly
suspected, or after using the restroom.
Otherwise, if resources permit, perform hand
rubbing with an alcohol-based preparation.
� Ensure availability of hand-washing facilities with
clean running water.
� Ensure availability of hand hygiene products
(clean water, soap, single use clean towels,
alcohol-based hand rub). Alcohol-based hand
rubs should ideally be available at the point of
care.
Personal protective equipment (PPE)
� ASSESS THE RISK of exposure to body
substances or contaminated surfaces BEFORE
any health-care activity. Make this a routine!
� Select PPE based on the assessment of risk:
� clean non-sterile gloves.
� mask and eye protection or a face shield.
Respiratory hygiene and cough etiquette
� Education of health workers, patients and visitors.
� Covering mouth & nose when coughing or sneezing.
� Hand hygiene after contact with respiratory
secretions.
� Spatial separation of persons with acute febrile
respiratory symptoms.
Background
Standard precautions are meant to reduce the risk
of transmission of blood borne and other pathogens
from both recognized and unrecognized sources.
They are the basic level of infection control precautions
which are to be used, as a minimum, in the care of all
patients.
Hand hygiene is a major component of standard
precautions and one of the most effective methods to
prevent transmission of pathogens associated with health
care. In addition to hand hygiene, the use of personal
protective equipment should be guided by risk assessment
and the extent of contact anticipated with blood and
In addition to practices carried out by health workers
when providing care, all individuals (including patients
and visitors) should comply with infection control
practices in health-care settings. The control of spread
of pathogens from the source is key to avoid transmission.
Among source control measures, respiratory
hygiene/cough etiquette, developed during the severe
acute respiratory syndrome (SARS) outbreak, is now
considered as part of standard precautions.
Worldwide escalation of the use of standard precautions
would reduce unnecessary risks associated with health
care. Promotion of an institutional safety climate helps
to improve conformity with recommended measures and
thus subsequent risk reduction. Provision of adequate
staff and supplies, together with leadership and education
of health workers, patients, and visitors, are critical
for an enhanced safety climate in health-care settings.
Important advice
� Promotion of a safety climate is a cornerstone of
prevention of transmission of pathogens in health care.
� Standard precautions should be the minimum level of
precautions used when providing care for all patients.
� Risk assessment is critical. Assess all health-care
activities to determine the personal protection that is
indicated.
� Implement source control measures for all persons
with respiratory symptoms through promotion of
respiratory hygiene and cough etiquette.
Standard precautions in health care
1. Hand hygiene
Summary technique:
1. Hand washing (40–60 sec): wet hands and apply
soap; rub all surfaces; rinse hands and dry thoroughly
with a single use towel; use towel to turn off faucet.
� Hand rubbing (20–30 sec): apply enough product to
cover all areas of the hands; rub hands until dry.
Summary indications:
� Before and after any direct patient contact and
between patients, whether or not gloves are worn.
� Immediately after gloves are removed.
� Before handling an invasive device.
tions, non-intact skin, and contaminated items, even if
gloves are worn.
� During patient care, when moving from a contaminated
to a clean body site of the patient.
� After contact with inanimate objects in the immediate
vicinity of the patient.
2. Gloves
excretions, mucous membranes, nonintact skin.
� Change between tasks and procedures on the same
patient after contact with potentially infectious material.
� Remove after use, before touching non-contaminated
items and surfaces, and before going to another patient.
Perform hand hygiene immediately after removal.
3. Facial protection (eyes, nose, and mouth)
� Wear a surgical or procedure mask and eye protection
(face shield, goggles) to protect mucous membranes of
the eyes, nose, and mouth during activities that are likely
secretions, and excretions.
4. Gown
� Wear to protect skin and prevent soiling of clothing
during activities that are likely to generate splashes or
� Remove soiled gown as soon as possible, and perform
hand hygiene.
5. Prevention of needle stick injuries.
Use care when:
� handling needles, scalpels, and other sharp instruments
or devices
� cleaning used instruments
� disposing of used needles.
6. Respiratory hygiene and cough etiquette
Persons with respiratory symptoms should apply
source control measures:
� cover their nose and mouth when coughing/sneezing
with tissue or mask, dispose of used tissues and masks,
and perform hand hygiene after contact with respiratory
secretions.
Health care facilities should:
� place acute febrile respiratory symptomatic patients at
least 1 metre (3 feet) away from others in common waiting
areas, if possible.
� post visual alerts at the entrance to health-care facilities
instructing persons with respiratory symptoms to
practise respiratory hygiene/cough etiquette
� consider making hand hygiene resources, tissues and
masks available in common areas and areas used for
the evaluation of patients with respiratory illnesses.
7. Environmental cleaning
� Use adequate procedures for the routine cleaning
and disinfection of environmental and other frequently
touched surfaces.
8. Linens
Handle, transport, and process used linen in a
manner which:
� prevents skin and mucous membrane exposures and
contamination of clothing
� avoids transfer of pathogens to other patients and or
the environment.
9. Waste disposal
� Ensure safe waste management.
secretions and excretions as clinical waste, in accordance
with local regulations.
� Human tissues and laboratory waste that is directly
associated with specimen processing should also be
treated as clinical waste.
� Discard single use items properly.
10. Patient care equipment
secretions, and excretions in a manner that prevents
skin and mucous membrane exposures, contamination
of clothing, and transfer of pathogens to other patients or
the environment.
� Clean, disinfect, and reprocess reusable equipment
appropriately before use with another patient.
Health-care facility recommendations for standard precautions.
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