Fungus a possible precursor of severe respiratory diseases in pigs

The fungus Pneumocystis carinii causes progressive pneumonia in pigs and is a possible “door opener” for secondary bacterial infections. (Photo: Michael Bernkopf/Vetmeduni Vienna)

Piglet  1

The fungus Pneumocystis carinii causes mild forms of progressive pneumonia in pigs. It has therefore not been considered to be of high diagnostic relevance. A team from Vetmeduni Vienna has now shown this pathogen to be very prevalent among Austrian pigs, indicating that its role has so far been underestimated. Pneumocystis appears to be a sort of “door opener” for secondary bacterial infections. The results were published in two studies in the journals The Veterinary Journal and Journal of Veterinary Diagnostic Investigation.

Respiratory diseases in pigs typically involve multiple infections from different pathogens. Some pathogens 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, as it probably requires other underlying conditions to sufficiently weaken the immune defence of the animals first.

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

Pneumocystis 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,” explains Christiane Weissenbacher-Lang of the Institute for Pathology and Forensic Veterinary Medicine, describing the possible progression of the infection.  

Fungus detectable in living pigs only with lung lavage

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. The team around Weissenbacher-Lang therefore 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.

Read the press release "Fungus a possible precursor of severe respiratory diseases in pigs" for further information. 2

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