Pig producers know that the colder months typically herald an increased risk of respiratory disease for their herds, and this is backed up by data from the BPEX Pig Health Scheme (BPHS) that shows a national trend for an increase in the incidence of porcine respiratory disease during the autumn and winter. Alvaro Hidalgo of Elanco Animal Health considers the problem, and strategies to tackle it
Regarded as one of the most serious disease problems in modern pig production, respiratory disease not only affects the health status of a herd, but is also known to cause significant economic losses to the swine industry worldwide. Often the result of a battery of pathogens – some causing disease in their own right and some taking advantage of a weakened immune state – the extent of the disease is often determined by a combination of environmental, management and genetic factors. The common reference to Porcine Respiratory Disease Complex (PRDC) when discussing respiratory disease in pigs reflects this multi-factorial nature.
One of the main pathogens involved in PRDC is Mycoplasma hyopneumoniae, the causative agent of a condition called enzootic pneumonia (EP), a disease that remains a serious concern for the pig industry around the world.
The most common (and often only) clinical sign of EP is coughing due to damage to lung tissue. The cough is often described as ‘barking’ in nature and is more evident when pigs are moved. In severe cases, which are usually complicated with concurrent infections, then high temperatures, lethargy and lack of appetite may also be seen. Yet some infected pigs may not appear ill or cough at all, and this disease has been shown to seriously compromise growth and feed conversion rates.
While EP in itself has implications to health and productivity, the most significant effect that it has is to ‘open the door’ to secondary pathogens. As the mechanisms of the lungs that act to keep airways clear and the immune function are compromised, these opportunistic pathogens are able to colonise the lungs and significantly enhance the severity of disease. This makes controlling M hyopneumoniae infection a key strategy in the control of bacterial pneumonia.
In herds that are endemically infected, M hyopneumoniae is transmitted from pig to pig by direct nose-to-nose contact or in aerosolised droplets generated by coughing and sneezing, making it possible to spread between different barns or units within a herd. With the potential to spread rapidly through a group, transmission can also occur between sows and their offspring. Breeding sows can remain persistently infected and have the potential to spread M hyopneumoniae to their piglets even after six parities. This means piglets may be colonised with M hyopneumoniae even before weaning. In a recent study, M hyopneumoniae was found in three-week-old piglets in nearly 70% of herds tested in different European countries.
Neighbouring farms may be a risk factor as M hyopneumoniae has been shown to be able to spread on the wind. The minimum distance between pig farms to theoretically avoid airborne transmission has been calculated to be at least 3km.
Control strategies
EP can be treated with appropriate antibiotics, but with a wall of evidence indicating that production losses can occur in animals that don’t even appear to be affected, and also that animals can become infected at a very young age, it’s essential to take a proactive approach to the whole herd to prevent production losses.
Dealing with the presence of enzootic pneumonia in a herd usually involves a variety of approaches including treatment, improving house conditions and management of the animals and the use of vaccines. Managing practices should be focused on minimising the risk of transmission between pigs by assuring an optimal environment for the animals (see Table 1).
Vaccination is critical and one of the most widespread methods of disease control. The proper use of M hyopneumoniae vaccines reduces the economic impact of the disease by improving daily weight gain and feed conversion rates, allowing animals to reach slaughter weight quicker. Vaccination also reduces clinical signs by limiting lung damage, which has the knock-on effect of lowering treatment costs. The development of single-dose vaccines, such as Stellamune Once, has made vaccination much easier to include into routine farm management.
Timing of vaccination is important for an optimum control of EP. Ideally, vaccine should be administered before infection occurs. Since M hyopneumoniae is likely to be present in the piglets before the third week of age, implementation of an early vaccination strategy is recommended in order to achieve protective immunity.
In addition, there’s a lower pathogenic burden, which means less interference with the immune response. Vaccination with Stellamune Once induces immunity within two weeks of administration and can be used in piglets from seven days of age. This protection is not short-lived either, lasting until the end of the fattening period.
Porcine respiratory disease is common and costly, affecting pig herds across the globe. While elimination of the most significant pathogens involved is immensely difficult due to their nature of spread, production losses can be minimised and herd health improved through strategic control and early use of vaccination.
Early intervention Stellamune Once at seven days of age means that pigs should already be protected at weaning, making them better able to handle subsequent exposure to the pathogen during the nursery stage.
Increased risk of porcine respiratory disease in colder months
Enzootic pneumonia (EP) caused by the organism Mycoplasma hyopneumoniae results in distinct changes in the lungs of affected pigs, so it’s possible to monitor for disease at slaughter.
BPHS results show that EP-like lesions tend to increase in winter months across the country and that, overall, the trend during the past few years has been a worrying increase. Seasonal trends were investigated in the period 2011-2012, indicating that the EP-like lesions score increased in the winter. Although the general situation improved in spring 2012 for the majority of the regions, it was still worse than at the same time the previous year. In accordance with those findings, a more detailed study on the relationship between M hyopneumoniae infection and climatological conditions also found similar results.
Animals born in autumn that entered finishing units in winter (when lower temperatures were recorded) and reached slaughter in spring had the highest probability of being infected by M hyopneumoniae.