Turkeys Found to be Resistant to Human H1N1 Virus

Researchers in Italy have found that turkeys are resistant to the human influenza A H1N1 virus under experimental conditions.

21 October 2009

6 minute read

Terregino and colleagues at the Istituto Zooprofilattico Sperimentale delle Venezie (IZSVe), Legnaro, Italy investigated the resistance of turkeys to experimental infection with an early 2009 Italian human influenza A(H1N1) virus isolate. Their paper has been published in the latest issue of Eurosurveillance.

They concluded that the pandemic H1N1 influenza virus is not likely to be transmitted to meat turkeys and does therefore not represent an animal health or food safety issue for this species.

The experiment highlights the difficulties of carrying out this type of research with rapidly changing viruses, as only this week, the H1N1 has been found in a turkey flock in Ontario, Canada. So far, details have not emerged over the severity of the disease in the Canadian birds. It is also possible that either the virus has mutated in a way to become more pathogenic to turkeys and/or that the Canadian turkeys were less resistant to the virus than those in Italy.

Introduction

In their report, Terregino and colleagues explain that following the emergence of the human pandemic influenza A(H1N1)v virus in spring 2009, questions about the circulation of this virus in an animal reservoir were raised by international organisations. In particular, three aspects appeared to be of relevance, namely implications on animal health, aspects of food safety, and epidemiological aspects related to animals being infected with a human virus and perpetuating a parallel channel of infection in the animal reservoir.

Turkeys (Meleagris gallopavo) are highly susceptible to type A influenza virus infection and have been infected in the past with viruses of swine origin, according to the report. In August 2009, infection of two turkey flocks in Chile with the human influenza A(H1N1)v virus was reported. The genetic profile of the virus appeared to be closely related (similarity ranging between 99.7 per cent and 100 per cent) to the strain that was circulating in the human population in Chile at the time.

The aim of the IZSVe experiment was to establish the susceptibility of turkeys of different ages to infection with the human virus and to assess whether it would be detectable in the blood or in tissues of meat birds following administration of a high viral dose.

Materials and Methods

Commercially available turkeys were used in this study. The birds originated from a flock that was serologically negative for all avian influenza subtypes, including influenza A(H1N1)v, by agar gel immunodiffusion test (AGID) and enzyme-linked immunosorbent assay (ELISA) and negative for influenza A virus by real-time reverse transcription-PCR (RRT-PCR) on cloacal and tracheal swabs.

Challenge of turkeys was carried out with the influenza A virus isolate A/Italy/2810/2009(H1N1). The virus was isolated from a human case detected in Verona, Italy, in specific pathogen-free (SPF) embryonated hens' eggs via the amniotic cavity and was characterised according to chapter on swine influenza in the World Organisation for Animal Health (OIE) Manual of Diagnostics Tests and Vaccines for Terrestrial Animals.

The aim of experiment 1 was to evaluate the presence of virus in blood, meat and viscera. A group of 10 70-day-old turkeys were oro-nasally infected with 100µl of the challenge virus containing 107 EID50. On days 1, 2, 3, 4 and 5 post infection, blood was collected from each bird from the wing vein, mixed with anticoagulant, and the establishment of viraemia was evaluated by RRT-PCR. If blood samples yielded positive results, up to two birds presenting viraemia were killed humanely on the day of testing. When blood samples yielded negative results and no animals showed clinical signs, two turkeys were killed humanely on a random basis. In case of any death, lungs, intestine, superficial and deep pectoral muscles and thigh muscles were collected on the day of death.

In experiment 2, clinical signs, tracheal and cloacal shedding and seroconversion following experimental infection were investigated. A group of 12 21-day-old turkeys were used in this experiment. All animals were experimentally infected oro-nasally with 100µl of challenge virus containing 107 EID50. Twice a day, clinical signs were recorded. On days 2, 4, 6, 10 and 15 post infection, tracheal and cloacal swabs were collected from each bird. On day 14 and 21 post infection, blood samples were collected to evaluate seroconversion.

Results

Mild, non-specific clinical signs were observed in the 21-day-old birds a few days following administration of the challenge virus. These signs were considered to be non-specific because the birds did not exhibit the conjunctivitis, sinusitis or nasal discharge typical of low pathogenicity avian influenza infection.

In both experimental groups, the virological and molecular results from all collected samples were negative. Seroconversion was detected in 41.6 per cent, 8.3 per cent and 33.3 per cent of birds belonging to the younger age group by ELISA, AGID and HI tests (only with the homologous antigen), respectively.

Discussion

The data reported here indicate that both 21- and 70-day-old turkeys are resistant to infection with early strains of the human influenza A(H1N1)v virus, according to the report. Despite the high infectious dose and the mutation in the HA gene, it was not possible to achieve infection or to detect virus in blood, respiratory and enteric organs or in muscles of experimentally infected birds.

Terregino and co-authors were surprised at the evidence of seroconversion in a proportion of the infected poults. Since active infection was not achieved, they say it is likely that the seroconversion is related to the high viral dose administered. In any case, antibodies were detectable only with the homologous virus, thus indicating that intra-subtypic cross-reactivity was below HI detection limits.

The researchers conclude that, unless the human influenza A(H1N1)v virus undergoes substantial changes, the risk that meat turkeys become infected with the virus is negligible. They see no reason to be concerned about the animal health or food safety implications of this infection in this species.

Reference

Terregino C., De Nardi R., Nisi R., Cilloni F., Salviato A., Fasolato M. and Capua I. 2009. Resistance of turkeys to experimental infection with an early 2009 Italian human influenza A(H1N1)v virus isolate. Euro Surveill. 2009;14(41):pii=19360.