Information AboutNipah Virus |
| CATEGORIES ABOUT HENIPAVIRUS | |
| mononegavirales | |
| viral diseases | |
| zoonoses | |
| SHOPPER'S DELIGHT | |
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'' Hendravirus '' '' Nipahvirus '' ''Henipavirus'' is a genus of the family '' Paramyxoviridae '', order '' Mononegavirales '' containing two members, '' Hendravirus '' (originally ''Equine Morbillivirus '', EMV) and '' Nipahvirus '' (the word ‘henipavirus’ is a concatenation of the two virus names). The henipaviruses are characterised by their large size (18.2 kilobases; Wang et al., 2001), their natural occurrence in Pteropid Fruit Bat s (flying foxes), and their recent emergence as Zoonotic pathogens capable of causing illness and death in Domestic Animal s and Human s. HENDRA VIRUS Emergence Hendra virus was discovered in September 1994 when it caused the deaths of thirteen Horse s, and a trainer at a training complex in Hendra, a suburb of Brisbane in Queensland , Australia . The index case, a mare, was housed with 23 other horses after falling ill and died two days later. Subsequently, 19 of the remaining horses succumbed with 12 dying. Both the trainer and a stable hand were involved in nursing the index case and both fell ill within one week of the horse’s death with an influenza-like illness. The stable hand recovered while the trainer died of respiratory and renal failure. The source of virus was most likely frothy nasal discharge from the index case. A second Outbreak occurred in August 1994 (chronologically preceding the first outbreak) in Mackay 1000km north of Brisbane resulting in the deaths of two horses and their owner (Field et al., 2001). The owner assisted in necropsies of the horses and within three weeks was admitted to hospital suffering from meningitis. He recovered, but 14 months later developed neurologic signs and died. This outbreak was diagnosed retrospectively by the presence of Hendra virus in the brain of the patient. A serosurvey of wildlife in the outbreak areas was conducted and identified pteropid fruit bats as the most likely source of Hendra virus with a seroprevalence of 47%. None of the other 46 species sampled were positive. Virus isolations from the reproductive tract and urine of wild bats indicated that transmission to horses may have occurred via exposure to bat urine or birthing fluids (Halpin et al, 2000). Outbreaks Three more incidents, in Cairns in January 1999 and October 2004, and in Townsville in December 2004, each resulted in the death of one horse. A vet involved in autopsy of the horse from the 2004 Townsville incident developed a Hendra-related illness soon after and recovered. The distribution of black and spectacled flying foxes covers Townsville and Cairns, and the timing of incidents indicates a seasonal pattern of outbreaks possibly related to the seasonality of fruit bat birthing. As there is no evidence of transmission to humans directly from bats, it is thought that human infection only occurs via an intermediate host. Pathology Flying foxes are unaffected by Hendra virus infection. Symptoms of Hendra virus infection of humans may be respiratory, including Haemorrhage and Oedema of the lungs, or Encephalitic resulting in Meningitis . In horses, infection usually causes pulmonary oedema and congestion. NIPAH VIRUS Emergence Nipah virus was identified in 1999 when it caused an outbreak of neurological and respiratory disease on pig farms in peninsular Malaysia , resulting in 105 human deaths and the culling of one million pigs (Field et al., 2001). In Singapore , 11 cases including one death occurred in abattoir workers exposed to pigs imported from the affected Malaysian farms. Symptoms of infection from the Malaysian outbreak were primarily encephalitic in humans and respiratory in pigs. Later outbreaks have caused respiratory illness in humans, increasing the likelihood of human-to-human transmission and indicating the existence of more dangerous strains of the virus. Outbreaks Six more outbreaks of Nipah virus have occurred since 1998 , one in India and five in Bangladesh . All outbreak sites lie within the range of Pteropus species (Pteropus giganteus). As with Hendra virus, the timing of the outbreaks indicates a seasonal effect.
Eleven isolated cases of Nipah virus encephalitis have also been documented in Bangladesh since 2001. Nipah virus has been isolated from Lyle's flying fox (Pteropus lylei) in Cambodia (Reynes et al, 2005) and viral RNA found in urine and saliva from P. lylei and Horsfield's roundleaf bat (Hipposideros larvartus) from Thailand (Wacharapluesadee, et al, 2005). The Cambodian strain shows 98% identity with the virus causing the 1998 outbreak. No infection of humans or other species have been observed in Cambodia or Thailand. Pathology In humans, the infection presents as fever, headache and drowsiness. Cough, abdominal pain, nausea, vomiting, weakness, problems with swallowing and blurred vision are relatively common. About a quarter of the patients have seizures and about 60% become comatose and might need mechanical ventilation. In patients with severe disease, their conscious state may deteriorate and they may develop severe hypertension, fast heart rate, and very high temperature. Nipah virus is also known to cause relapse encephalitis. In the initial Malaysian outbreak, a patient presented with relapse encephalitis some 53 months after his initial infection. There is no definitive treatment for Nipah encephalitis, apart from supportive measures, such as mechanical ventilation and prevention of secondary infection. Ribavirin , an antiviral drug, was tested in the Malaysian outbreak and the results were encouraging, though further studies are still needed. In animals, espicially in pigs, the virus causes porcine respiratory and neurologic syndrome also known as barking pig syndrome or one mile cough . CAUSES OF EMERGENCE The emergence of henipaviruses parallels the emergence of other zoonotic viruses in recent decades. SARS Coronavirus , Australian Bat Lyssavirus , Menangle Virus and probably Ebola Virus are also harboured by bats and are capable of infecting a variety of other species. The emergence of each of these viruses has been linked to an increase in contact between bats and humans, sometimes involving an intermediate domestic animal host. The increased contact is driven both by human encroachment into the bats’ territory (in the case of Nipah, specifically pigpens in said territory) and by movement of bats towards human populations due to changes in food distribution and loss of habitat. There is evidence of habitat loss for flying foxes both in South Asia and Australia (particularly along the east coast) as well as encroachment of human dwellings and agriculture into the remaining habitats, creating greater overlap of human and flying fox distributions. REFERENCES
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