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An initial analysis today from Poland's National Veterinary Institute of nine viruses from cats infected with H5N1 avian influenza suggests they are related to viruses found in the country's poultry and wild birds, according to a statement translated and posted by Avian Flu Diary, an infectious disease news blog. The sicknesses and deaths in cats have been reported from a wide geographic area, with some noted in indoor cats, making the source of the virus unclear.

The report said the viruses belong to the same genotype and are most closely related to a sample collected in June from a white stork. The genotype was seen during the peak of the 2022-23 season and was detected mainly in poultry in Wielkopolska province and in wild birds in multiple parts of Poland.

The report didn't note any mutations that may make the virus more adapted to mammals. Scientists noted that the feline H5N1 viruses they have examined so far came from a single unidentified source and that more detailed genetic analysis is under way to better gauge the zoonotic potential.

CDC updates H5N1 technical report In other avian flu developments, the US Centers for Disease Control and Prevention (CDC) recently updated its technical information on H5N1, which covers the latest sporadic infections in humans and outbreaks in wild birds, poultry, and other animals. (The document, dated June 30, doesn't include information on the H5N1 detections in Polish cats.)

The CDC said the H5N1 viruses currently circulating in wild birds and poultry don't have the ability to easily bind to human upper-airway tract receptors. Though outbreaks in US poultry flocks have declined substantially over spring and summer, the H5N1 strain continues to circulate in wild birds, posing an ongoing transmission threat that requires close monitoring.

Regarding H5N1 in mammals, the CDC said data suggest the virus may evolve to replicate more efficiently in the respiratory tract, but so far the changes haven't been linked to increased transmissibility in humans.

Infections with Avian Influenza A(H5N1) virus in cats in Poland

OFFLU is closely monitoring information from Poland regarding unusual deaths in domestic cats in multiple households throughout the country. These cases have been reported widely in the press during the past week.

Felidae, both wild and domestic, are known to be susceptible to Influenza A(H5N1) viruses with most cases appearing to be the result of ingestion of infected carcasses of wild birds (Chen et al 2016, Frymus et al 2021).

A report from the Polish Chief Veterinary Officer issued on 26 June indicated that nine of 11 affected cats subjected to testing were found to be infected with Influenza A(H5N1) virus. The severe and rapid course of the infection is also consistent with reports of this disease in Felidae. Felidae infected with Influenza A(H5N1) viruses can show a range of clinical signs including listlessness, loss of appetite, severe depression, fever, neurological disease, respiratory and enteric signs, jaundice, and death. Clinical signs would be expected to develop within a few days of exposure to the virus. Other fatal cases of infection in cats with Influenza A(H5N1) have been reported from Europe and North America during the current clade 2.3.4.4b panzootic including a fatal case of Influenza A(H5N1) reported from a cat in France with dyspnea and nervous signs (Briand et al 2023). Exposure to infected wild birds or poultry were considered the most likely modes of infection.

It has been shown that Influenza A(H5N1) viruses in the goose/Guangdong/1/96-lineage can invade the body via the intestine in experimentally infected cats and cause extensive damage to endothelial cells lining blood vessels throughout the body. This resulted in damage to multiple organs including the intestine, liver, lung, kidney and brain with multifocal necrosis detected in some organs (Reperent et al 2012).

Investigations are required to better understand this cluster of cases to assess links between suspected cases and possible routes of exposure, additional testing of sick and dead cats to establish that the virus is present in other cats and the cause of the disease being seen, and rapid genotypic and phenotypic characterisation of detected viruses for evidence of changes likely to indicate capacity to spread between mammals. Investigations are being undertaken at present by Polish authorities.

Early reports indicated that not all suspect cases had outdoor access suggesting that a direct role from infected wild birds is unlikely as a common source. The wide geographical distribution of suspected cases suggests that the primary mode of spread in these cases is not cat-to-cat transmission. It is likely that infected cats would shed virus via the gut and respiratory tract so any suspected cases should be isolated from other pets, and those handling them should wear appropriate personal protective equipment (PPE). Earlier scientific advice from Europe on preventing influenza A(H5N1) in cats should be considered (Thiry et al 2009).

OFFLU will continue to monitor this outbreak and provide updated information when available.

(Additional note by me: info is very slow so far, but a little more came out this morning https://twitter.com/k_pyrc/status/1675777629822017538?s=46&t=cHNB1hq6Rvo76m9WMTo1tA)