Nearly 18 months ago (Dec 15th, 2016) the New York City Health Department issued an unusual Statement On Avian H7N2 In Cats at a Manhattan animal shelter.
While cats are known to be susceptible to some novel flu strains (see Catch As Cats Can) this outbreak was remarkable due to its size (initially involving 45 cats), its location (NYC), and the virus involved - a relatively uncommon avian LPAI H7N2 virus not reported in the United States in over a decade.Over the holidays the story continued to escalate when the NYC DOH released a statement announcing a mild Human H7N2 Infection in a veterinarian who was treating sick cats. Additionally, more than 400 cats - across multiple facilities - were said to have been infected.
Although the risk to human health was believed low, the Health Department offered guidance to those who have had contact with cats in these shelters, and urged people to avoid `nuzzling and close facial contact' with sick cats.Human infection with LPAI H7N2 has only rarely been reported, with only a couple of cases on record in the United States (in 2002 and 2003), and 4 people who were presumed to have been infected in the UK in 2007 following local outbreaks in poultry.
In all cases, illness was described as mild and self limiting.While only one human infection was reported, and the incident was declared over by late January, this was a bit of a wake up call on the potential spread of a zoonotic avian flu virus by a companion animal.
At the time, the CDC wrote:
Why is CDC concerned about H7N2?
As part of CDC’s mission to protect the public from emerging health threats, CDC monitors changes in flu viruses found in human and animal populations. Finding a bird flu virus in an unexpected animal, like a cat, is always concerning, because it means the virus has changed in a way that may pose a new health threat. Animal viruses that gain the ability to infect humans are especially concerning because most people will not have existing immune protection against such viruses.
Also, there is potential for a pandemic (a global outbreak of disease) to occur when a new animal virus gains the ability to infect humans and also has the ability to spread efficiently from person to person. For these reasons, these incidents must be carefully investigated and appropriate actions taken to ensure that there is no ongoing spread of the novel virus among people.Since then, we've learned a good deal more about the H7N2 virus, including:
- Last May, in J. Virology: Virulence Of A Novel H7N2 Virus Isolated From Cats In NYC - Dec 2016, we saw a follow up report on the NYC outbreak, which found the H7N2 virus will require additional adaptation before it poses a substantial human health threat.
- Last November, in EID Journal: Avian H7N2 Virus in Human Exposed to Sick Cats,we saw another study that found the human H7N2 virus bound to both α2,6-linked (mammalian) and α2,3-linked (avian) sialic acids, an important trait for any species jumping avian flu virus to acquire, although virulence remained low.
- Followed by EID Journal: Characterization Of A Feline Influenza A(H7N2) Virus last December, which found:
All of which serves as prelude to a new study, published last week in the journal Influenza & Other Respiratory Viruses, which documents both the airborne and fomite detection of the avian H7N2 virus at the quarantine facility where roughly 500 infected cats were housed.Direct contact transmission of feline H7N2 subtype viruses was detected in ferrets and cats; in cats, exposed animals were also infected via respiratory droplet transmission. These results suggest that the feline H7N2 subtype viruses could spread among cats and also infect humans. Outbreaks of the feline H7N2 viruses could, therefore, pose a risk to public health.
You'll want to read the full (open access) PDF, but I've excerpted the abstract below. When you return, I'll have a postscript.
Detection of an Avian Lineage Influenza A(H7N2) Virus in Air and Surface Samples at a New York City Feline Quarantine Facility
Francoise M. Blachere,William G. Lindsley, Angela M. Weber,Donald H. Beezhold,Robert E. Thewlis,Kenneth R. Mead,John D. Noti
First published: 16 May 2018
In December 2016, an outbreak of low pathogenicity avian influenza (LPAI) A(H7N2) occurred in cats at a New York City animal shelter and quickly spread to other shelters in New York and Pennsylvania. The A(H7N2) virus also spread to an attending veterinarian. In response, 500 cats were transferred from these shelters to a temporary quarantine facility for continued monitoring and treatment.
The objectives of this study was to assess the occupational risk of A(H7N2) exposure among emergency response workers at the feline quarantine facility.
Aerosol and surface samples were collected from inside and outside the isolation zones of the quarantine facility. Samples were screened for A(H7N2) by quantitative RT‐PCR and analyzed in embryonated chicken eggs for infectious virus.
H7N2 virus was detected by RT‐PCR in 28 of 29 aerosol samples collected in the high‐risk isolation (hot) zone with 70.9% on particles with aerodynamic diameters > 4 μm, 27.7% in 1‐4 μm, and 1.4% in < 1 μm. Seventeen of 22 surface samples from the high‐risk isolation zone were also H7N2‐positive with an average M1 copy number of 1.3 x 103. Passage of aerosol and surface samples in eggs confirmed that infectious virus was present throughout the high‐risk zones in the quarantine facility.
By measuring particle size, distribution, and infectivity, our study suggests that the A(H7N2) virus had the potential to spread by airborne transmission and/or direct contact with viral‐laden fomites. These results warranted continued A(H7N2) surveillance and transmission‐based precautions during the treatment and care of infected cats.While the avian H7N2 virus - at least as a human health threat - doesn't appear particularly robust, this study found concentrations of airborne virus in the quarantine facility's `hot zone' roughly equivalent to what has been previously documented in several health care facilities during an H1N1 influenza season.
And roughly 25% were `respirable'; light enough to remain airborne for a extended period of time and small enough to be easily drawn deeply into the lungs when inhaled.The authors wrote:
Thus, our results support both airborne and fomite-mediated A(H7N2) transmission as potential transmission routes amongst cats. Because the deposition site of any respiratory pathogen within the airway ultimately affects disease kinetics and pathogenesis, transmission-based precautions were pivotal to protecting quarantine staff and volunteers.For more on the potential for companion animals to serve as an intermediate host for influenza viruses with pandemic potential, you may wish to revisit:
Emerg. Microbes & Infect.: Virulence, Transmissibility & Evolution of Canine H3N2 Influenza Viruses
PLoS One: Evidence of Subtype H3N8 Influenza Virus Infection among Pet Dogs in China