Influenza A Pandemic (H1N1) 2009 Virus Infection in Domestic Cat

Influenza A pandemic (H1N1) 2009 virus continues to rapidly spread worldwide. In 2009, pandemic (H1N1) 2009 infection in a domestic cat from Iowa was diagnosed by a novel PCR assay that distinguishes between Eurasian and North American pandemic (H1N1) 2009 virus matrix genes. Human-to-cat transmission is presumed.

Infl uenza viruses are typically host specifi c; aquatic birds are considered the primary reservoir. However, interspecies transmission does occur (1)(2)(3)(4)(5)(6)(7)(8)(9) and occasionally leads to novel host-adapted strains. Interspecies transmission of infl uenza virus has been a public health concern because of the possibility that, through reassortment, a novel strain with zoonotic potential could emerge. The recent infection of dogs with equine infl uenza virus (H3N8) (2) and of swine with human infl uenza virus (H1N2) (4) are particularly intriguing because the former resulted in infl uenza becoming endemic in dogs and the latter resulted in a documented reassortment event between human and swine infl uenza viruses. Such concern has escalated with the recent emergence of the novel quadruple-reassorted infl uenza virus (H1N1) [pandemic (H1N1) 2009] in humans (10). Although infection and transmission of the virus have occurred primarily among humans, occasional transmission from infected persons to susceptible animals (e.g., swine, turkeys, ferrets) has been documented (11). The likelihood of pandemic (H1N1) 2009 infection of domestic pets has been considered less likely (www.cdc.gov/h1n1fl u/ qa.htm, www.avma.org/public_health/infl uenza/new_virus/default.asp, www.usda.gov/wps/portal/?navid=USDA_ H1N1); however, we report a confi rmed case of pandemic (H1N1) 2009 virus infection in a domestic cat that had been in contact with persons who had recently experienced infl uenza-like illness.

The Case
A 13-year-old, castrated male, domestic cat that lived indoors in a single-cat household was brought to the Iowa State University Lloyd Veterinary Medical Center because of depression, inappetance, and respiratory signs of 4 days' duration. The cat was gregarious and interacted closely with family members in the household. The family members noted that the cat was reluctant to lie in lateral recumbency and instead rested in sternal recumbency with neck extended, which was indicative of dyspnea. The cat's vaccination status was up to date. Before the onset of clinical signs in the cat, 2 of the 3 family members had experienced an undiagnosed infl uenza-like illness-an upper respiratory tract infection characterized by fever, coughing, and myalgia-that lasted 3 days. Onset of the cat's clinical signs was noted 6 and 4 days after onset of illness for the fi rst and second family members, respectively.
At the time of examination, the cat had bilateral adventitial lung sounds (wheezes), was afebrile, and was clinically dehydrated. Radiographs of the thorax showed a bilateral caudodorsal alveolar pattern (Figure). Cytologic and microbiologic examination of bronchoalveolar lavage (BAL) fl uid showed foamy macrophages (65%), nondegenerate neutrophils (25%), and small lymphocytes (10%). Clinicopathologic fi ndings suggested a moderate, predominantly macrophagic, mixed infl ammatory process. Standard microbial culture of BAL aliquots yielded no substantial growth of aerobic or anaerobic bacteria. Radiographic and cytologic fi ndings were inconsistent with bacterial or parasitic pneumonia and not supportive of allergic airway disease. A viral cause was considered most likely; however, the cat was given amoxicillin with clavulanate (125 mg orally 2×/day) to reduce the possibility of secondary bacterial pneumonia. Notable fi ndings from laboratory testing (complete blood count, serum biochemistry, urinalysis, and total thyroxine measurement) were moderate leukopenia characterized by a moderate lymphopenia, modest hemoconcentration, and a slightly elevated thyroxine level. Lymphopenia was consistent with acute viral infection.
PCR testing (Feline URD Panel; Idexx Laboratories, Westbrook, ME, USA) of a BAL sample showed negative results for Chlamydophila felis, feline calicivirus, feline herpesvirus-1, Bordetella bronchiseptica, and Mycoplasma felis. Results of feline immunodefi ciency virus (antibody) and feline leukopenia virus (antigen) testing (Idexx SNAP FIV/FeLV Combo Test; Idexx Laboratories) were also negative, ruling out the potential that viral-induced immunosuppression was a concurrent factor. For the following reasons we included pandemic (H1N1) 2009 on our list of The cat was discharged from the medical center after diagnostic testing and correction of dehydration. A veterinarian (B.A.S.) visited the home to monitor the cat's clinical status and administer subcutaneous fl uids (120-160 mL) until the cat's appetite improved; adventitial lung sounds resolved within 3 days. Reassessment 1 week later showed

Conclusions
Because the cat was from a single-animal household and remained indoors, he was presumably infected through contact with the family members. Attempts to retrospectively confi rm pandemic (H1N1) 2009 infection in the family members have been unsuccessful, but additional testing of archived biologic samples is being conducted. Although more surveillance and studies are needed to determine susceptibility of companion animals to the pandemic (H1N1) 2009 virus, possible reverse zoonotic transmission (humans to animals) remains a concern. Indeed, cases in a domestic dog and other felids have been confi rmed (11) (www.cdc.gov/h1n1fl u/qa.htm, www. avma.org/public_health/infl uenza/new_virus/default.asp, www.usda.gov/wps/portal/?navid=USDA_H1N1). Implications of pandemic (H1N1) 2009 virus infection in companion animals are 1) apparent human-to-animal transmission; 2) broader host range for the virus; 3) potential endemic establishment of infl uenza in companion animals; 4) possible transmission of infl uenza from compan-ion animals to other species, including humans; and 5) the need to reevaluate companion animals as potential reservoirs or intermediate hosts for reassortment of infl uenza virus. This case emphasizes the need for close monitoring for interspecies transmission of infl uenza virus and reinforces the need for collaboration among many disciplines, a cornerstone of the One Health Initiative (www. onehealthinitiative.com).