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Henipavirus infection in humans is caused either by the Nipah virus or Hendra henipavirus species. For both these species, flying foxes, also called pteropid fruit bats, act as reservoir hosts.
- A reservoir host means an animal in which the virus survives and multiplies without causing any symptoms or disease.
- A reservoir is required for the completion of the life cycle of the virus before it infects humans.
Hendra henipavirus infection cannot be transmitted from one human to another. The infection occurs when humans come in contact with infected horses or their body tissues or fluids. The horses get the infection from the urine of infected bats. The infection cannot be transmitted directly from the infected bats to humans.
The other disease-causing species called the Nipah virus gets transmitted to humans when they come in contact with infected pigs or bats. The consumption of date palm sap contaminated with the excretion of infected bats acts as a common means of Nipah virus infection in humans.
Besides the possibility of directly infected bats to human transmission, another difference between Hendra henipavirus and Nipah virus infections is the occurrence of person-to-person transmission of Nipah virus through close contact, including exposure to respiratory droplets, with infected people. This is more likely to occur when someone takes care of a person infected with the Nipah virus.
What are Henipaviruses?
Henipavirus is a genus of single-stranded RNA (viruses that have single-stranded RNA as their genetic material) enveloped viruses that belong to the Paramyxovirus family.
Among the five species of Henipaviruses identified so far, two species, namely, Nipah virus and Hendra henipavirus, can infect and cause serious diseases in humans and animals. The other three species of Henipaviruses (Cedar henipavirus, Ghanaian bat henipavirus, and Mojiang henipavirus) are not known to be pathogenic (causing disease in) to humans.
Although the reservoir hosts for Henipavirus (pteropid bats) are found throughout the tropics and subtropics, Henipavirus outbreaks in humans have only occurred in Northern Australia and Southeast Asia. Of the two pathogenic species, Hendra henipavirus infection has been reported almost every year since 1994 in the eastern states of Australia. Nipah virus outbreaks are reported almost every year in India and Bangladesh and were reported in 1999 in Malaysia and Singapore.
What are the symptoms of Henipavirus infection?
Symptoms generally appear within 5 to 16 days of being infected with the virus. Rarely, the symptoms may take as long as two months to appear.
Both the pathogenic species, Hendra henipavirus, and Nipah virus, generally present as an influenza-like illnesses. Symptoms may include:
As the disease progresses, the virus may cause encephalitis (severe inflammation of the brain). When this occurs, the person may present with:
Severe disease may even cause death due to serious respiratory or brain involvement.
About four out of seven Hendra henipavirus infections may result in the death of the infected individual (case fatality ratio of 57 percent). The case fatality ratios for Nipah virus infection generally range from 40 to 70 percent but have been as high as 100 percent in some human outbreaks.
How is Henipavirus infection diagnosed?
The diagnosis of Henipavirus infection is done by health professionals based on:
- Your medical history includes a history of travel to areas where the infection is common, exposure to certain animals (such as bats, pigs, and horses), and the appearance of signs and symptoms.
- A detailed medical examination includes a chest examination and the presence of any abnormal reflexes that may suggest encephalitis.
- Certain lab tests such as:
- Enzyme-linked immunosorbent assay of serum or cerebrospinal fluid (CSF).
- Reverse transcription–polymerase chain reaction of serum, CSF, or throat swabs.
- Virus isolation from CSF or throat?swabs.
Is Henipavirus infection curable?
There is no definitive cure or treatment for Henipavirus infection. Treatment mainly consists of supportive care and management of complications including encephalitis and pneumonia.
Many people recover without any long-term complications, whereas some may have lingering brain or lung involvement.
The antiviral drug ribavirin has shown effectiveness in test-tube studies although its clinical usefulness is unknown. A type of immunotherapy, called monoclonal serotherapy, has been proposed for the treatment of Hendra henipavirus infection in Australia.
Is there a vaccine for Henipavirus infection?
Presently, there is no clinically approved vaccine to prevent Henipavirus infection. Several studies are underway to develop effective vaccines against the Nipah virus and Hendra henipavirus for human use.
A vaccine for use in horses has been licensed in Australia to prevent Hendra henipavirus infection. Such vaccines have the potential for future use in humans to prevent Henipavirus infection.
How can you prevent Henipavirus infection?
Because there is no effective Henipavirus vaccine for human use, the best way to avoid infection is by avoiding coming in contact with the infected animals (bats, sick horses, pigs, or their excretions) while traveling to endemic areas.
- While visiting such areas, one must avoid consuming raw date palm sap or its products.
- Avoid coming in contact with infected people, particularly in the case of Nipah virus infection that can transmit through person-to-person contact.
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