Could this family of viruses that you have never heard of cause our next pandemic?

If we were to ask Americans what disease outbreaks the world has experienced in the past 3 years, I suspect almost everyone would be able to identify COVID-19 (caused by the SARS-CoV-2 virus). Probably a large number, but certainly less would also be able to name influenza, likely by using its colloquial name of the “flu.” My guess is that if we pressed for more, a minority of Americans would be also able to identify RSV (respiratory syncytial virus) and possibly monkeypox (recently renamed by the CDC as MPox). I would be impressed if more than a handful of people would be able to recall the health alerts in the U.S. for Candida auris, drug-resistant gonorrhea, increased rates of syphilis, the drug-resistant bacterial infections (Pseudomonas aeruginosa) with artificial tears and eye drops, the outbreaks of norovirus, the hepatitis of unknown etiology in children, or the most recent outbreaks of malaria in Florida and Texas. I suspect that no lay person would realize that we had a larger than usual outbreak of human metapneumovirus infections at the beginning of this year and into the spring, unless they were one of the many infected with this virus.

Of course, there have been many more outbreaks than this that have received relatively little attention in the media and press, including outbreaks that we have had in the U.S., specifically polio in New York and measles in Ohio.

Among the many other outbreaks that occurred in parts of the world such as Marburg virus disease and Lassa fever, there was one that really caught my attention and caused me to do a double-take, and yet, I doubt any one other than infectious disease experts, public health experts or virologists knows anything about this virus.

In August 2022, a novel henipavirus named Langya virus caused an outbreak in China among 35 farmers and local residents that likely contracted the infection from shrews. The virus was isolated from patients with severe pneumonia. We already knew about two other henipaviruses – Nipah virus and Hendra virus. The case fatality rate for henipavirus infections in humans is approximately 70%. Hendra virus was first identified in 1994 in specimens taken mostly from horses, but also some humans with respiratory and neurologic disease in Australia. The source of the virus is flying fox bats (aka fruit bats). Hendra virus is not of significant pandemic concern because the virus primarily infects horses and humans are generally only infected by contact with the secretions or tissues of infected horses. Further, no human-to-human spread has been identified.

Nipah virus is a different story. Nipah (pronounced “Nee-paw”) is also transmitted by fruit bats, but it infects humans and pigs. It can cause inflammation and swelling of the brain, a condition doctors refer to as encephalitis. The illness can range from mild to severe, including death. Outbreaks have historically occurred in India and Bangladesh.

Nipah virus presents more of a potential pandemic threat than Hendra virus because while the earliest outbreaks appear to have resulted from transmission from bats à pigs à humans with little, if any, human-to-human transmission, human-to-human transmission regularly occurs in more recent outbreaks. Close contact with a person with Nipah virus disease can cause transmission through body fluids – nasal secretions, respiratory droplets, blood and urine. Transmission most often occurs within families and within health care settings.

However, Langya virus presents more a of potential pandemic threat in my mind than the other henipaviruses for the following reasons:

• The first known spill-over event was in August of 2022. (In case you don’t understand why that would increase the pandemic threat relative to the other two viruses in its family – Hendra and Nipah viruses – it is because the other two viruses have been circulating in the animal and human population much longer, and therefore, have already had more opportunity to develop more efficient transmission in humans and to have caused a major outbreak by now, but haven’t yet.
• Rats and shrews can serve as intermediate hosts for Langya virus and are distributed globally, which greatly increases the risk of infections in humans, as people living in large metropolitan areas are far more likely to encounter rats than pigs (Nipah virus) or horses (Hendra virus).
• The fruit bat is migratory, which means that it can carry the virus with it to new geographic areas.
• The Langya virus is a novel and antigenically distinct from its cousins, Nipah and Hendra viruses, which means that there is no significant pre-existing immunity, nor is there likely much cross-over protection (in other words, antibodies to Nipah virus are unlikely to be protective against Langya virus.

What this means is that we need to conduct more research into these novel viruses to better understand their pathogenesis, to develop treatments and hopefully develop effective vaccines.