Research suggests that shrews may be natural reservoirs of LayV, from which the virus can hop into humans by chance. — Photos: Filepic
Researchers from China, Singapore and Australia reported on Aug 4 (2022) the identification of the Langya henipavirus (LayV) in a throat swab sample from a 53- year-old woman in the town of Langya in Shandong, China.
Their finding was published in a letter in the New England Journal of Medicine.
The genome of the LayV is most closely related to the Mojiang henipavirus, which was first isolated from rats in an abandoned Yunnan mine in south China.
Henipaviruses belong to the Paramyxoviridae family of viruses, which includes measles, mumps and many respiratory viruses that infect humans.
Several other henipaviruses have been discovered in bats, rats and shrews, from Australia to South Korea and China, but only the Hendra, Nipah, and now LayV, viruses are known to infect people.
Langya virus
The researchers that identified LayV had been monitoring patients with fever at three hospitals in Shandong and Henan between April 2018 and August 2021.
Sunday Star reported the official naming of the then unknown virus behind the mysterious outbreak infecting both pigs and humans on April 11, 1999.
They identified 35 patients – mostly farmers – with acute LayV, of whom 26 were infected with only LayV (and no other pathogens).
These 26 patients had:
- Fever (100% of the patients)
- Fatigue (54%)
- Cough (50%)
- Anorexia, or loss of appetite (50%)
- Myalgia, or muscle pain (46%)
- Nausea (38%)
- Headache (35%), and
- Vomiting (35%).
These symptoms were accompanied by:
- Thrombocytopenia, or low platelets (35%)
- Leukopenia, or low white blood cells (54%),
- Impaired liver function (35%), and
- Impaired kidney function (8%).
The symptoms ranged from severe pneumonia to a cough.
Most stated in a questionnaire that they had been exposed to an animal within a month of their symptoms appearing.
According to the researchers, findings from the patients with acute LayV infection suggest that it was the cause of febrile illness based on the following factors:
- LayV was the only potential pathogen detected in 26 of the 35 patients (74%).
- In paired serum samples that were obtained from 14 patients during the acute and convalescent phases of infection, the IgG (immunoglobulin G, a type of antibody) titres in 86% of the convalescent phase samples were four times as high as those in the acute phase samples.
- Viraemia (presence of viruses in the bloodstream) was associated with acute LayV infection.
- Patients with pneumonia had higher viral loads than those without pneumonia.
The researchers did not find strong evidence of LayV spreading between people as there was no obvious association between the cases either in location or time.
There was also no close contact or common exposure history among the patients, which suggests that the infection in the human population may be sporadic.
But retrospective contact-tracing was only done on 15 family members of nine patients.
The researchers said that it “revealed no close-contact LayV transmission, but the sample size was too small to determine the status of human-to-human transmission for LayV”.
To determine the potential animal origin of LayV, tests were done on goats, pigs and cattle in the villages of the infected patients.
Antibodies against LayV were found in goats (three out of 168, or 2%) and dogs (four out of 79, or 5%).
Tissue and urine samples were taken from 25 species of small wild animals to ascertain the presence of LayV RNA (ribonucleic acid).
LayV RNA was predominantly detected in shrews (71 out of 262, or 27%), a finding that suggests the shrew may be a natural reservoir of LayV, infecting themselves and infecting people by chance.
It was unclear how people were infected in the first place, whether directly from shrews or an intermediate animal.
The researchers conclude that a lot of work is needed to ascertain how LayV is spreading in shrews and how people get infected.
They stressed the need for a global surveillance system to detect viral spread from animals to humans, and rapid communication to avoid more pandemics like Covid-19.
Hendra and Nipah viruses
An electron microscopy picture of HenV (A and B) attacking a Vero cell. — Universiti Malaya
The Hendra virus (HeV) was first isolated in 1994, during an outbreak of respiratory and neurologic disease in horses and humans in the Brisbane suburb of Hendra, Australia.
The outbreak involved 21 stabled racehorses and two humans who died.
To date, seven humans have contracted HeV following exposure to the body fluids, tissues or excretions of infected horses, with four dying – a death rate of 57%.
HeV has not been reported outside of northeast Australia.
A commercial HeV vaccine for horses has recently been licensed in Australia.
Malaysia was the first country in the world to encounter the Nipah virus (NiV), which sparked an outbreak here in 1998-1999.
It resulted in the near decimation of the local pig-rearing industry, which was then the largest in Asean, with about a million pigs culled.
Many of the humans who survived the infection have been left with residual complications.
The initial NiV cases were reported near Ipoh in September 1998.
Four of these 28 cases tested positive for IgM (immunoglobulin M) antibodies against Japanese Encephalitis (JE) and a JE outbreak was declared by the Health Ministry.
The pigs were sold and transferred out of Perak.
By the end of 1998, more cases were reported in Bukit Pelandok in Port Dickson, Negri Sembilan.
In March 1999, Dr Chua Kaw Bing, then attached to Universiti Malaya’s Department of Medical Microbiology, isolated NiV from a patient being treated at the university’s hospital, who was from Sungai Nipah village.
The outbreak eventually caused 283 cases and 109 deaths with a death rate of 38.5%.
An NiV outbreak (11 cases, one death) was also reported in Singapore among slaughterhouse workers in March 1999.
Since then, there have been annual outbreaks in Bangladesh starting from 2001, as well as outbreaks in eastern India.
The death rate of NIV ranges from about 40% to 75% depending on the local clinical management capability.
Most human NiV infections in Malaysia resulted from unprotected exposure to secretions of sick pigs or their contaminated tissues.
Subsequent outbreaks in Bangladesh and India, however, were most likely due to consumption of fruits or fruit products that had contact with infected fruit bats.
These bats, which are the natural reservoir of NiV, have been found in Indonesia, Philippines, Thailand, Cambodia, Ghana and Madagascar.
Human-to-human NiV transmission have been reported among family and caregivers of the infected through close contact with their secretions and excretions.
Similarly, healthcare workers in Bangladesh and India have been reported to be infected due to providing care.
NiV outbreaks have also been reported in domestic animals like pigs, horses, goats, sheep, cats and dogs.
An infected pig can be asymptomatic (have no symptoms), but some develop fever, difficulty breathing and neurological symptoms like trembling, twitching and muscle spasms.
The death rate in pigs is usually low, except in young piglets.
There is no treatment or vaccine available for NiV in either humans or animals.
A need for surveillance
Only three henipaviruses – HeV, NiV, and now LayV – are known to infect humans.
Although there has been no NiV outbreak in Malaysia since about two decades ago, only the very brave can vouch that it will not recur.
Could LayV occur in Malaysia?
Only time will tell.
As such, it is very important for the Health and Agriculture ministries to provide the public updated information about its surveillance of both NiV and LayV in humans and animals.
Dr Milton Lum is a past president of the Federation of Private Medical Practitioners Associations and the Malaysian Medical Association. For more information, email starhealth@thestar.com.my. The views expressed do not represent that of organisations that the writer is associated with. The information provided is for educational and communication purposes only, and it should not be construed as personal medical advice. Information published in this article is not intended to replace, supplant or augment a consultation with a health professional regarding the reader’s own medical care. The Star disclaims all responsibility for any losses, damage to property or personal injury suffered directly or indirectly from reliance on such information.
