What Causes Henipavirus?

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.

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:

• Fever
• Headache
• Body ache or muscle ache
• Dizziness
• Running nose
• Cough 
• Fatigue
• Sore throat
• Vomiting 

As the disease progresses, the virus may cause encephalitis (severe inflammation of the brain). When this occurs, the person may present with:

• Confusion
• Seizures or abnormal body movements
• Unconsciousness or altered consciousness
• Coma

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.

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.

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.

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.

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.