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Nipah virus ? Facts Sheet (WHO, October 7 2011, edited)

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  • Nipah virus ? Facts Sheet (WHO, October 7 2011, edited)

    [Source: World Health Organization, Weekly Epidemiological Record, full PDF document: (LINK). Edited.]

    Nipah virus ? Facts Sheet (1)


    The Nipah virus is an emerging zoonotic virus (that is, a virus transmitted to humans from animals). In infected people, the Nipah virus causes a severe illness characterized by inflammation of the brain (encephalitis) or respiratory diseases. It can also cause severe disease in animals, such as pigs, resulting in significant economic losses for farmers.

    The Nipah virus is closely related to Hendra virus. Both are members of the genus Henipavirus, a new class of virus in the Paramyxoviridae family.

    Although the Nipah virus has caused only a few outbreaks, it infects a wide range of animals and causes severe disease and death in people, making it a public health concern.



    Outbreaks

    The Nipah virus was first recognized in 1999 during an outbreak among pig farmers in Malaysia. Since then, there have been 12 additional outbreaks, all in South Asia.



    Transmission

    During the initial outbreaks in Malaysia and Singapore, most human infections resulted from direct contact with sick pigs or their contaminated tissues. Transmission is thought to have occurred via respiratory droplets or through contact with the tissue of a sick animal.

    During 2001?2008 in outbreaks in Bangladesh and India, consumption of fruit or fruit products (such as raw date-palm juice) contaminated with urine or saliva from infected fruit bats was the most likely source of infection.

    During later outbreaks (2005?2008) in Bangladesh and India, Nipah virus was spread directly from human to human when uninfected people came into close contact with secretions and excretions from infected people, such as saliva, urine, vomitus or diarrhoea. In Siliguri, India, in 2001 transmission of the virus was reported to have occurred within a health-care setting where 75% of cases in the outbreak occurred among hospital staff or visitors. From 2001 to 2008, around half of all reported cases in Bangladesh were caused by human-to-human transmission.



    Signs and symptoms

    Human infections range from asymptomatic infection to fatal encephalitis. Infected people initially develop influenza-like symptoms of fever, headaches, myalgia (muscle pain), vomiting and sore throat. This may be followed by dizziness, drowsiness, altered consciousness, and neurological signs that indicate acute encephalitis.

    Some people may also experience atypical pneumonia and severe respiratory problems, including acute respiratory distress. Encephalitis and seizures occur in severe cases, and patients may progress to coma within 24 hours to 48 hours.

    The incubation period (that is, the interval from the time of infection to the onset of symptoms) varies from 4 days to 45 days.

    Most people who survive acute encephalitis make a full recovery but around 20% are left with residual neurological consequences, such as persistent convulsions and personality changes. A small number of people who recover subsequently relapse or develop delayed-onset encephalitis.

    In the long term, persistent neurological dysfunction is observed in >15% of people.

    The case-fatality rate is estimated to be 40?75%; however, this rate varies by outbreak depending on local capabilities for surveillance.



    Diagnosis

    Infection with the Nipah virus can be diagnosed by a number of different tests:
    • serum neutralization;
    • enzyme-linked immunosorbent assay (ELISA);
    • polymerase chain reaction (PCR) assay;
    • immunofluorescence assay;
    • virus isolation by cell culture.

    Treatment

    There are no medicines or vaccines available to treat infection with the Nipah virus. Intensive supportive care that treats symptoms is the main approach to managing the infection in people.



    Natural host: fruit bats

    Fruit bats of the Pteropodidae family ? particularly species belonging to the Pteropus genus ? are the natural hosts for the Nipah virus. There is no apparent disease in fruit bats.

    It is assumed that the geographical distribution (Map 1) of Henipaviruses overlaps with that of Pteropus. This hypothesis was reinforced by evidence of Henipavirus infection in Pteropus bats found in Australia, Bangladesh, Cambodia, China, India, Indonesia, Madagascar, Malaysia, Papua New Guinea, Thailand and Timor-Leste.

    In 2008, African fruit bats of the Eidolon genus, of the Pteropodidae family, were found to have antibodies against the Nipah virus and the Hendra virus, indicating that these viruses might be present within the geographical distribution of Pteropodidae bats in Africa.



    Nipah virus in domestic animals

    Outbreaks of infection with the Nipah virus in pigs and other domesticated animals (horses, goats, sheep, cats and dogs) were first reported during the initial Malaysian outbreak in 1999. Many pigs had no symptoms but others developed acute feverish illness, laboured breathing, and neurological symptoms, such as trembling, twitching and muscle spasms. Generally, mortality was low except in young piglets.

    These symptoms are not dramatically different from other respiratory and neurological illnesses that occur in pigs. Infection with the Nipah virus should be suspected if pigs also have an unusual barking cough or if human cases of encephalitis are present.

    The virus is highly contagious in pigs. Pigs are infectious during the incubation period, which lasts from 4 days to 14 days.



    Prevention

    Controlling the virus in domestic animals

    There is no vaccine to protect against infection with the Nipah virus. Routine cleaning and disinfection of pig farms (with sodium hypochlorite or other detergents) is expected to be effective in preventing infection.

    If an outbreak is suspected, the area where animals are kept should be quarantined immediately. The culling of infected animals ? with close supervision of burial or the incineration of carcasses ? may be necessary to reduce the risk of transmission to people. Restricting or banning the movement of animals from infected farms to other areas can reduce the spread of the disease.

    Because outbreaks of infection in domestic animals have preceded human cases, establishing an animal health surveillance system to detect new cases is essential to provide early warning for veterinary and human public-health authorities.



    Reducing the risk of infection in people

    Because there is no vaccine, the only way to reduce infection in people is by raising awareness of the risk factors, and educating people about the measures they can take to reduce their exposure to the virus.

    Educational public-health messages should focus on:
    • reducing the risk of bat-to-human transmission.
      • Efforts to prevent transmission should focus first on decreasing bats? access to date-palm sap. Freshly collected date-palm juice should be boiled, and fruit should be thoroughly washed and peeled before consumption;
    • reducing the risk of human-to-human transmission.
      • Close physical contact with people infected with the Nipah virus should be avoided. Gloves and protective equipment should be worn when taking care of ill people. Regular hand-washing should be carried out after caring for or visiting sick people;
    • reducing the risk of animal-to-human transmission.
      • Gloves and other protective clothing should be worn while handling sick animals or their tissues, and during slaughter and culling procedures.

    Controlling infection in health-care settings

    Health-care workers caring for patients with suspected or confirmed Nipah-virus infection, or handling specimens from them, should implement standard infection control precautions.

    Samples taken from people and animals suspected to be infected with the Nipah virus should be handled by trained staff working in suitably equipped laboratories

    (1) This WHO fact sheet was last updated in July 2009.


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