Influenza is a viral disease that affects many species of animals.
The world health community continues to monitor the progress of the avian flu virus as it moves through the bird population around the globe. This influenza subtype is an H5N1 isolate. Poultry with this subtype of virus have infected people.
The ability of the virus to infect people from those who carry the virus is being watched very closely. There is currently no immunity to this subtype in the human population.
If this virus subtype adapts so it can be passed from person to person, this strain has the potential to be the next influenza subtype to affect the human population.
Influenza is also a major disease concern in swine. For many years, we only isolated the H1N subtype from the swine population. We now see many strains, with the H1N1 and the H3N2 subtypes being the most common.
The virus that affects swine has the ability to exchange genetic material with other influenza viruses of different species. A poultry/swine/human triangle for genetic material exchange and disease transmission occurs for influenza virus.
The great human influenza pandemic of 1918 that killed 20 million people worldwide was an influenza virus that originated in swine.
There is a concern that the passage of influenza between humans and swine does occur in our swine barns. The flu vaccine that was administered to our staff last fall included subtypes H3N2 and H1N1. It is our recommendation that all workers who come into contact with swine be vaccinated with the human influenza vaccine. This is for the good of workers and pigs.
Case Study No. 1
A 1,500-sow, three-site production farm was experiencing a cough in piglets from 15 days old to weaning. This was a well-managed farm with good production. The entire sow herd was being vaccinated quarterly with a commercial influenza vaccine containing both the H1N1 and H3N2 subtypes of influenza virus.
Blood samples were obtained from sows for serologic examination. This farm had very high antibody levels in the sow herd. The samples had high titer levels, up to 1:640 on 75% of the sows sampled. Laboratory work on piglets yielded an influenza infection by fluorescent antibody testing as well as histological (tissue) examination.
Since this farm was already on a flu vaccination program, we wanted to get an isolate from the farm to use for farm-specific vaccine production. We submitted nasal swabs from farrowing room piglets for virus isolation. An H3N2 subtype of influenza virus was isolated.
A site-specific influenza vaccine was made from this isolate and used in the sow herd. The coughing by piglets in the farrowing crates ceased.
Case Study No. 2
We were called to a 200-sow, farrow-to-finish farm. This single-site operation had a history of respiratory disease problems, including positive titers for porcine reproductive and respiratory syndrome, Actinobacillus pleuropneumonia (APP), Mycoplasmal pneumonia and H1N1 and H3N2 swine influenza virus.
Vaccination for respiratory disease consisted of two doses of a commercial mycoplasma vaccine in the early nursery stage.
The clinical syndrome on this farm was coughing and mortality in the finisher, primarily after 16 weeks of age. Sick pigs were treated with antibiotics, but some mortality occurred due to sudden death in finishing pigs. Respiratory outbreaks occurred from 14 weeks of age through market age.
Typically, multiple finishing rooms would come down with clinical signs at the same time. After these rooms resolved, the syndrome would become quiet again until a new population of naïve pigs filled the rooms, and the process would be repeated.
This farm would endure a respiratory disease outbreak every four months. Diagnostic tests confirmed the presence of mycoplasma and influenza. At times, we would find APP and PRRS.
Since the mycoplasma and influenza organisms were commonly diagnosed, we added a two-strain influenza vaccine to the current mycoplasma vaccination program. We are currently going on two years with only minor respiratory disease problems.
Diagnostic workups are vital to identify the organisms that are key components in any disease complex. In the first case study, we had high antibody levels in the sow herd, but were able to isolate influenza virus from the nasal swabs of coughing piglets. Control of strain variation can be the difference between success and failure in a vaccination program.
The vaccination of workers for the protection of people from pigs, and pigs from people, should be part of the influenza control program.