In July 2023, H5N1 Highly Pathogenic Avian Influenza (HPAI) infection was confirmed in cats at two private animal shelters in Seoul, Korea. All infected or deceased cats had consumed raw duck-based pet food, and HPAI virus was detected in the product. Genetic sequencing showed a 99.9–100% match between the virus in the pet food and that in infected cats, supporting foodborne transmission. The manufacturing plant had suspended sterilization in May 2023, raising concerns about inadequate safety protocols. Emergency measures included a product recall, surveillance of 286 pet cats, and monitoring of 102 shelter animals, all of which tested negative. No human infections; even so, authorities emphasized personal hygiene and wildlife monitoring. This case highlights the need for stricter safety controls in pet food production and the importance of a One Health approach in managing zoonotic risks. Given the close contact between companion animals and humans, preparedness for potential cross-species transmission should be reinforced.

• Highly Pathogenic Avian Influenza (HPAI)
• Cat
• Animal Shelter
• Pet Food
• One Health

Kim H, Lee E, Yoon H (2025) Infection Routes and Emergency Countermeasures for H5N1 HPAI in Cats at Private Animal Shelters in Korea. Clin Res Infect Dis 9(1): 1071.

HPAI: Highly Pathogenic Avian Influenza; MAFRA: Ministry of Agriculture, Food and Rural Affairs; APQA: Animal and Plant Quarantine Agency; M gene: Matrix gene

Highly Pathogenic Avian Influenza (HPAI) is a viral infection that primarily affects birds, but cases have also been reported in mammals, including humans, pigs, and cats [1]. Genetic mutations, particularly in the PB2 gene, enhance the virus’s ability to bind to mammalian receptors, facilitating cross-species transmission [2,3]. In addition, environmental conditions and interspecies contact play roles in transmission among mammals. H5N1 HPAI infections have been documented in cats in Thailand [4], Germany [5], North America, and Poland [6,7], as well as in cats and dogs in Italy [8]. These spillover events have raised growing concerns about the zoonotic potential of HPAI viruses.

HPAI has repeatedly affected poultry and wild birds in Korea since the 2003/2004 winter season. These outbreaks have involved various H5 clades and genotypes, including H5N1, H5N6, and H5N8 [9]. The 2022/2023 epidemic was caused by H5N1 and concluded with the last confirmed case at a meat duck farm on April 14, 2023. However, just a few months later in July 2023, H5N1 HPAI was confirmed in cats at two private animal shelters in Seoul [10], marking the country’s second feline HPAI virus infection following a H5N6 case in a stray cat in 2016 [11]. This study investigates the potential infection routes and describes the emergency responses and coordinated countermeasures implemented to contain the outbreak in private cat shelters in Seoul in 2023.

In Korea, the notification of suspected cases, diagnosis, and response to HPAI outbreaks should be carried out in accordance with the Guidelines for Avian Influenza Prevention [12]. Suspected clinical samples from cats presented at veterinary clinics were first tested by a private diagnostic laboratory, then referred to a university laboratory, where H5 antigen was detected. The Animal and Plant Quarantine Agency (APQA) subsequently confirmed the infection as H5N1 HPAI [13]. Following confirmation, the Ministry of Agriculture, Food and Rural Affairs (MAFRA) coordinated emergency response efforts and facilitated collaboration with relevant government agencies. This study draws on the epidemiological investigation conducted by APQA [14], as well as official press releases from MAFRA [10,15-19], and the Seoul Metropolitan Government [20-23].

Epidemiology of HPAI in Cats

In July 2023, H5N1 HPAI was confirmed in nine cats from two private animal shelters in Seoul, located about 5.5 km apart. The affected cats were Korean Shorthairs, aged 2–4 years in the Yongsan shelter and 13 years or older in the Gwanak shelter, with an approximately equal male-to-female ratio. All were rescued strays kept indoors in multiple connected rooms without individual cages, allowing free movement and contact among cats.

On July 25, two cats at the Yongsan shelter showed symptoms such as fever and respiratory distress and soon died. Initial testing by a private lab confirmed Influenza A, later identified as H5N1 HPAI via rRT-PCR by Seoul National University and APQA [13]. Three more cats at the shelter tested positive on July 28. Of the 40 cats housed there, 38 died between June 25 and July 22 [19]. The two survivors tested negative for avian influenza virus but positive for H5 antibodies [14,20]. Elsewhere, on July 29, two cats being treated for similar symptoms at the Gwanak shelter also died and were confirmed to have H5N1 HPAI. Between July 23 and 29, five of the 11 cats at this shelter died [11,18]. On August 3, two more cats tested positive, bringing the total number of confirmed cases there to four [16,19].

Through environmental sample testing, the matrix (M) gene was detected at both shelters, indicating widespread contamination. In Yongsan, it was found on surfaces such as floors, doors, walls, and refrigerators. The detection of the virus in cat feces and the shared use of litter boxes in Gwanak suggest that direct transmission among cats was plausible. Indirect transmission via humans and equipment cannot be ruled out, as the M gene was found on the shelter staff’s clothing and shoes in Yongsan, and in a vacuum cleaner in Gwanak.

The on-site investigation found that all infected or deceased cats had consumed raw duck-based pet food. At the Gwanak shelter, two pet food products (one chicken- based and one duck-based) were identified. H5N1 HPAI was detected only in the duck-based product [14,18]. In Yongsan, no pet food remained for testing, but the two surviving, antibody-positive cats had also consumed the same brand. Genetic sequencing showed a 99.9–100% match between the virus found in infected cats and the contaminated pet food, classified as clade 2.3.4.4b, the same lineage responsible for the epidemic from November 2022 to April 2023 in Korea [14].

Back-tracing of the pet food manufacturer revealed that electronic beam sterilization was suspended on May 25, 2023, as a cost-saving measure. Products were only frozen at -25? for 48 hours before delivered to consumers. The contaminated products were manufactured between late May and July 2023, using duck meat processed in February during the HPAI outbreak. It cannot be ruled out that the food was produced using latently infected ducks. However, as no virus was detected in farm samples collected before slaughter, the exact route of contamination remains unclear.

Similar cases of HPAI detection in pet food was reported in Poland, the virus was detected in chicken- based pet food consumed by cats, though it was unclear whether contamination occurred before or after packaging [7]. HPAI virus detection have been reported in imported frozen poultry meat in Korea (2001), Japan (2003), and Germany (2007), as well as in experimental studies where the virus was isolated in chicken meat [24].

The possibility of virus introduction via infected cats or mechanical transmission by a shelter staff cannot be excluded. As infections occurred only in cats that consumed the same brand, cat-to-cat transmission is considered unlikely. And the timeline makes both scenarios less likely. Both shelters admitted their most recent cats before March 2023, over three months prior to symptom onset in July. And the last detection of avian influenza in wild birds in Seoul reported in February, leaving a gap of over four months before symptoms appeared. In other countries, cases have been reported where companion animals were infected through direct contact with wild birds. April 2023, a dog in Ontario, Canada, tested positive after contact with a wild goose [6]. In Italy, one cat and five dogs on an HPAI- affected farm were infected after free access to indoor and outdoor areas [8].

Emergency Response and Countermeasures

A recall was issued for all raw pet food produced between May 25 and August 1, 2023 (date of detection), by the manufacturer of the H5N1-positive product. Consumers were notified through delivery tracking and public announcements. A total of 13,200 units (1,980 kg) were recalled and destroyed. MAFRA and Seoul authorities also conducted emergency surveillance on 286 pet cats; none showed HPAI symptoms during a 14- day observation [13,14]. MAFRA inspected 13 other raw pet food manufacturers. HPAI was not detected in any of the 110 samples, but one company violated sterilization protocols [17,19,23].

Korea Disease Control and Prevention Agency (KDCA) monitored for 10 days shelter staff and veterinarians who had contact with infected cats. Neither developedsymptoms or tested positive for the virus [19]. KDCA advised that although transmission cat-to-human transmission is extremely rare, strict personal hygiene should still be maintained [10,15]. Shelter animal surveillance covered all 25 Seoul districts. All 102 tested animals (57 dogs, 45 cats) were negative [21,23]. Additionally, surveillance in 430 aviary facilities, including zoos, bird farms, and animal cafés, found no positive cases [17,23]. Wild bird monitoring was strengthened, with monthly testing increasing from 35 to 90 birds and over 100 fecal samples. The Ministry of environment stressed the public to report any wildlife deaths observed near migratory bird habitats as part of enhanced surveillance efforts [17].

The three weeks control period ended on August 21, 2023, with no further outbreaks following the last confirmed case on August 3 [19]. The outbreak was most likely caused by contaminated raw duck-based pet food, as infections were confirmed only in cats that consumed the same brand, indicating no direct or indirect cat-to-cat transmission. Although the exact route of contamination remains unknown, the case demonstrated effective multi- agency coordination and a successful One Health response. It also underscores the need for systematic management of companion animals and strengthened surveillance and prevention in high-risk settings such as shelters and zoos [26,27]. Furthermore, given the close contact between infected cats and humans, preparedness for potential zoonotic transmission should not be overlooked.

This study was supported by the Animal and Plant Quarantine Agency under research project number N-1543068-2025-29-01.

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