CSC

BLOG

Microbes and Microbiota: Benefits and Risks

More on H5N1 and Cats: The Case for Worrying

First, a thank you to readers who have requested more information about avian influenza in cats. I also thank risk communication scholar Peter Sandman for suggesting the ‘case for worrying’ format to assist in presenting evidence when people are worried and confused.

Here is my perspective of the case for and against worrying about avian influenza H5N1 and cats, followed by highlights from key references.

Highlights of Evidence from Published Studies

Multi-dose inoculation study by Vahlenkamp and colleagues at Federal Research Institute for Animal Health in Germany and Intervet UK (2008)

o   No disease transmission was observed for cats inoculated (combined oculo-nasopharyngeal route) at the lowest three doses (1, 100, and 10,000 egg infectious dose units (EID50), relative viral counts documented to infect 50% of embryonated chicken eggs).

o   Two of three cats inoculated at the highest dose (a million times the EID50) developed clinical symptoms and fatal outcomes. The third cat inoculated at the highest dose recovered and developed protective antibodies.

o   Cats immunized with low pathogenic H5N6 were fully protected from subsequent challenge at the highest H5N1 dose (a million times the EID50).

Review by Sreenivasan and colleagues from University of Kentucky (2024)

o   Cats exposed to H5N1 can show no signs of clinical infection or signs including conjunctivitis, periocular swelling, depression, lethargy, and oculonasal discharge, as well as severe and fatal signs of respiratory distress and neurological signs (e.g., circling, blindness).

o   Fatal infections were reported in small numbers of cats as sporadic cases or outbreaks in Germany, Poland, South Korea, and the US.

o   A poultry farm outbreak in Italy was not associated with disease transmission to a domestic cat and 5 dogs on the farm.

Systematic review by Coleman and Bemis of University of Maryland  (2024)

o   Of 41 studies on natural infections of avian influenza viruses in felines from 2003 through April of 2024, 27 studies reported on domestic cats in 13 countries (Austria, China, Egypt, France, Germany, Indonesia, Iraq, Italy, Poland, Spain, South Korea, Thailand, US).

o   Of avian influenza subtypes, H5N1 was most frequently reported in cats, followed by H5N6, H7N2, H9N2, and H3N8.

o   Although the authors offered some estimates for mortality rate, few studies reporting fatalities documented the actual number of cats exposed, and serology studies are inconsistent with high fatality rates.

o   Indonesia reported ~100 of 500 domestic cats sampled in 2008 were seropositive for H5N1 antibodies.

o   Some workers in direct contact with low pathogenic avian influenza H7N2-infected cats in shelter outbreaks became seropositive.

o   The authors report that transmission route (direct contact, ocular, oral, respiratory) and delivered viral doses likely impact disease presentation and severity in cats, consistent with general principles of dose-response assessment for humans and other animals.

Seroprevalence study by Cavicchio and colleagues from the Experimental Zooprophylactic Institute of Venice (IZSVe), Italy  (2024)

o   Influenza A viral infections in cats are sporadic and self-limiting even when high morbidity and mortality is reported in areas where outbreaks are reported in wild and domestic avian species.

o   Samples from healthy feral cats living in outdoor feline colonies hosted by companion animal shelters in 7 provinces in northeastern Italy (2021-2022) were negative for influenza A (and H5N1) in all 385 oropharyngeal swabs. Only one of 279 serum samples was H5-positive.

o   Considering recurring outbreaks for domestic (263) and wild birds (24) reported in the area in the same time period of the study, authors conclude transmission of influenza A including H5N1 to cats is rare.

Seroprevalence study by Duijvestijn and colleagues at University of Utrecht, The Netherlands and Stray Cat Foundation Netherlands (2024)

o   Serum was confirmed positive for antibodies to avian influenza H5 in 83 of 701 clinically healthy rural stray cats (65 confirmed) from nature preserves and nearby dairy farms and in none of 871 urban domestic cats sampled from 2020 to 2023 in The Netherlands.

o   Pharyngeal swabs or lung tissues were negative for influenza A virus in 230 cats with acute respiratory or neurologic signs.

o   Higher seroprevelance in stray cats was considered by the authors as evidence for more frequent exposure due to foraging (hunting and eating) wild birds.

o   The study authors recommend that people handling cats with respiratory or neurological signs use appropriate personal protective equipment (e.g., gloves, face shield, mask).

Some additional studies that may be of interest are listed below. If you would like a follow-up blog on additional studies, please submit a comment with your interest.

Margaret Coleman3 Comments