Practical On-Farm Solutions to Tackle Swine Influenza

Swine Influenza Virus (SIV) is known to be a primary respiratory pathogen for swine inducing typical lung lesions. In Europe and in Italy subtypes H1N1, H3N2 and H1N2 are almost endemic in many pig producing areas although with different prevalences in different countries in different times. In most of the cases SIV induces an acute infection of the respiratory tract whose consequences are depending on the “intrinsec pathogenicity/virulence” of a specific virus, the pig immune status and the pig’s immune system reactivity. In the field we may observe basically two different forms of Swine Influenza (SI).

The most common is the Epizootic form affecting adult animals of different ages, all at the same time or in a short period of time. It usually has a sudden acute onset with pigs showing clinical signs within the first 12 to 48 hours after being infected. Affected animals show great prostration, fever, anorexia, hard coughing, dyspnoea and nasal discharge. Secondary bacterial infections may contribute to complicate the course of the viral infection. In the Enzootic form are mostly affected young animals in the nursery period. The clinical appearance may be similar to the epizootic form but the final outcome is largely dependent by the dynamic of population immunity. This form is frequently seen in farrow-to-finish farms and when or where the mothers are not regularly vaccinated.

The gross lesions caused by SIV start to develop as soon as 24 hours after infection and are usually limited to apical and cardiac lobes of the lungs. In most severe cases almost all the lungs may be affected. Although Swine Influenza may be suspected every time there is a sudden acute respiratory disease affecting a large proportion of pigs in a herd, to confirm the diagnosis virus isolation or detection using a PCR is required. The best samples to submit are the lung tissue of dead animals or few nasal swabs taken from sick, highfever animals. The hemagglutinins and neuraminidases are then determined using specific inhibition tests. I would not suggest using serology to diagnose influenza because of the interference of both maternal antibodies in young animals and vaccine immunity in vaccinated animals. Of course there is no specific treatement for Swine Influenza. Affected animals only need careful nursing providing a good, warm and nicely ventilated environment. Antipiretics (aspirin or paracetamol) are very useful to treat pigs during the acute phase of the disease.

Antibiotic treatment may only be used to treat concurrent or secondary bacterial infections. Biosecurity measures (All In/All Out management of groups, quarantine period of incoming animals, strict management of accesses to pigs) play a major role in preventing SIV infection. Nevertheless, these measures alone are not enough to efficently prevent infection in densely pig populated areas where airborne spread may contribute to Influenza epidemics over relatively large geographical areas. Vaccination is therefore the most important tool to reduce the incidence of this infection/disease not only in sow herds but also in growing and finishing pigs. In Italy there are only two licensed inactivated vaccines on the market. Both have the H1N1 and H3N2 strains and only one has the new H1N2.

The evaluation of the economic effect of SI vaccination may be contradictory and certainly requires and accurate evaluation of prevalence (hence the need for a monitoring program) and costs (need to evaluate the cost of every single outbreak) in order to be able to evaluate the supposed benefits. In sow herds, besides protecting the mothers themselves, vaccination is aimed at reducing or possibly stopping transmission from the dam to the offsprings, so the supposed economic benefits will also be transferred – if we may say so – to the following production stages. Surveillance and active monitoring of SIVs changes remain a primary requirement.

Understanding where SIVs are coming from and how they enter in pig farms is also crucial. Despite the degree of protection provided by the available vaccines in experimental challenges appears to be more than satisfactory there is still the need to gather more scientific and economic evaluation of their real performances in the field before their acceptance becomes more widespread. Nevertheless, when correctly applied, vaccination is today by far the most efficient tool – available for veterinarians and producers - to prevent and control SI.