Henipaviruses are a group of emerging zoonotic RNA viruses belonging to the Paramyxoviridae family. They pose a public health concern due to their ability to cause severe illness and death in both humans and animals.
Types of Henipaviruses and Natural Hosts
The genus Henipavirus includes several notable members, with Hendra virus (HeV) and Nipah virus (NiV) being the most well-known. Hendra virus was first identified in September 1994 in Hendra, a suburb of Brisbane, Queensland, Australia, following an outbreak of severe respiratory disease in horses. Nipah virus was discovered in 1998 during an outbreak in Sungai Nipah, a village in Malaysia, where it initially affected pigs and humans.
More recently, Langya henipavirus (LayV) was identified in eastern China in late 2018, primarily in Shandong and Henan provinces. Fruit bats of the Pteropodidae family, commonly known as flying foxes, serve as the primary natural reservoir for most henipaviruses.
A natural reservoir is an animal population that harbors a virus without showing signs of disease, but can transmit it to other species. These bats can carry henipaviruses asymptomatically, shedding the virus through their urine, feces, and saliva. This allows the virus to persist in the environment, creating opportunities for spillover events to other animals and humans.
Transmission to Humans
Henipaviruses primarily transmit to humans through a process known as zoonotic spillover, where a pathogen moves from an animal population to a human one. This can occur through several pathways. Direct contact with the bodily fluids of infected fruit bats, such as urine or saliva, is one route. For instance, consuming fruit or raw date palm sap contaminated by bat secretions has been identified as a source of infection in some regions.
The virus can also be transmitted to humans through intermediate animal hosts. Hendra virus, for example, spreads from fruit bats to horses, which then transmit the virus to humans through close contact with their bodily fluids, such as respiratory secretions or blood. Similarly, Nipah virus has been transmitted to humans via pigs, particularly in occupational settings like pig farms, where close contact with infected swine occurred.
Human-to-human transmission has also been documented, particularly for Nipah virus. This occurs through close contact with an infected person’s respiratory secretions or other bodily fluids. Such transmission has been observed in household and healthcare settings.
Symptoms and Disease Progression
The incubation period for henipavirus infections ranges from 4 to 14 days, though some cases have reported an incubation period as long as 45 days. Initial symptoms are often non-specific and can include fever, headache, muscle pain, vomiting, and sore throat. These early signs can make diagnosis challenging as they resemble common illnesses.
The disease can progress severely, leading to two primary clinical syndromes. Acute respiratory illness may develop, with symptoms ranging from moderate breathing difficulties to severe acute respiratory distress syndrome (ARDS). Patients may experience a harsh cough and rapid breathing.
A more severe manifestation is fatal encephalitis, which involves inflammation of the brain. Symptoms include dizziness, drowsiness, altered consciousness, and neurological signs that can quickly progress to seizures, coma, and ultimately death within 24 to 48 hours. The case fatality rate for Nipah and Hendra virus infections is high, estimated to range from 40% to 75%, varying by outbreak and local healthcare capabilities. Some individuals who survive acute encephalitis may experience long-term neurological complications such as persistent seizures, personality changes, or other residual neurological conditions.
Prevention and Medical Management
Preventing henipavirus infection involves a combination of public health measures and personal safety practices. Avoiding exposure to sick animals, particularly pigs and horses in affected regions, is a primary recommendation. This includes practicing enhanced biosecurity on farms to minimize contact between livestock and bats. Additionally, avoid consuming raw date palm sap or fruits that may have been contaminated by bat urine or saliva.
For healthcare workers caring for infected patients, the use of appropriate personal protective equipment, such as gowns, gloves, eye protection, and N95 respirators, is important to prevent human-to-human transmission. Currently, there are no specific antiviral treatments or licensed vaccines available for henipavirus infections in humans. Medical care for infected individuals is primarily supportive, focusing on managing symptoms and providing necessary interventions like respiratory support and addressing neurological complications.
While a human vaccine is still under trial, a vaccine for horses against Hendra virus has been available in Australia since 2012. This veterinary vaccine helps prevent the disease in horses, thereby reducing the risk of transmission to humans.