Respiratory diseases in pigs typically involve multiple infections from different pathogens, some of which play a greater role than others in the progression of the disease.

The fungus Pneumocystis carinii is a relatively common cause of pneumonia in Austrian pigs, but its role has so far remained largely unexplored. Pneumocystis is considered to be less dangerous than other pathogens because it likely requires other underlying conditions to sufficiently weaken the immune defense of the animals first.

A research team from Veterinärmedizinische Universität Wien (Vetmeduni) in Vienna, Austria, has now demonstrated the susceptibility of piglets to the fungus as well as its relation to other pathogens in the progression of the disease. The research has shown that the fungus plays a more important role in pneumonia than previously assumed. Detecting pneumocystis in a medical examination requires a lung lavage, which is less stressful to the animals than other sampling methods.

Pneumocystis found in sick piglets of all age groups

The researchers began by testing stored tissue samples of sick piglets for the presence of the fungus and other pathogens. Pneumocystis was detected in piglets of all ages. In suckling piglets, only the fungus was detected in lung tissue. The older the piglets, the more bacteria could be detected. Pneumocystis itself was no longer as prevalent as in the suckling piglets. The fungus, however, appeared to have proliferated before the bacterial pathogens. This suggests that the fungus plays a role as a “door opener” for secondary infections.

“First, the fungus spreads along the alveolar walls. From there, it proliferates and fills the alveolar spaces. As a result, the lung tissue receives insufficient oxygen, and bacteria can reproduce better in the damaged tissue,” Christiane Weissenbacher-Lang of the Institute for Pathology & Forensic Veterinary Medicine at Vetmeduni explained of the possible progression of the infection.

The progress of the infection can be easily demonstrated in the laboratory using lung biopsies. In living pigs, however, this type of sampling is difficult and not suitable for routine testing. Weissenbacher-Lang's team tested whether oral fluid samples and lung lavages from sick pigs could be suitable for a diagnosis. Lung lavages are less stressful and easier to perform than biopsies. They also offer the advantage that material is collected from the entire lung.

The researchers demonstrated that it was possible to clearly diagnose even a weak infection with the material from a lavage. The presence of fungal DNA can be specifically demonstrated using molecular methods such as real-time polymerase chain reaction tests.

The test was designed to detect the strains typically found in pigs. It was determined that oral fluid samples were not suitable for diagnosing mild or moderate infections. Sampling through lung lavages, therefore, appears to be the best method for diagnosing the fungus in routine testing among living pigs.

Weissenbacher-Lang intends to conduct further tests to show that pneumocystis pneumonia can play a role as an additional factor in co-infections with other respiratory pathogens. If this is the case, it will be necessary to respond at some point. The high susceptibility demonstrated among the tested pigs shows that pneumocystis should not be underestimated, even if the fungus itself has so far been categorized as a low risk for pigs.

Lung lavage an option for routine testing

Respiratory diseases in pigs are an economic risk for farms, and the potential loss is great. Keeping the animals in pens requires high quality standards for ventilation alone. If a pathogen still manages to manifest in the pen, veterinary measures must be taken in time to keep the majority of the herd healthy. Lung lavages are a suitable method for regular testing of the herd.

Biopsies require the animals to be anaesthetized, and samples are collected under ultrasound guidance. The procedure is time consuming, stressful for the animal and a potential health risk. Lung lavages are much less stressful and take less time to perform. The pigs are anaesthetized only briefly. The lavage itself takes only a few minutes.

Lavages are a routine method used in human medicine. Veterinarians are also familiar with this procedure, so the method could be applied in the pen without any major adaptations necessary for testing.