Abstract
While Pneumocystis has been recognized as both a ubiquitous commensal fungus in immunocompetent mammalian hosts and a major opportunistic pathogen in humans responsible for severe pneumonias in immunocompromised patients, in pigs its epidemiology and association with pulmonary diseases have been rarely reported. Nevertheless, the fungus can be quite abundant in porcine populations with up to 51% of prevalence reported so far. The current study was undertaken to longitudinally quantify Pneumocystis carinii f. sp. suis and other pulmonary pathogens in a cohort of 50 pigs from five Austrian farms (i.e., 10 pigs per farm) with a history of respiratory disease at five time points between the first week and the fourth month of life. The fungus was present as early as the suckling period (16% and 26% of the animals in the first and the third week, respectively), yet not in a high amount. Over time, both the organism load (highest 4.4 × 105 copies/mL) and prevalence (up to 88% of positive animals in the third month) increased in each farm. The relative prevalence of various coinfection patterns was significantly different over time. The current study unravelled a complex co-infection history involving Pneumocystis and other pulmonary pathogens in pigs, suggesting a relevant role of the fungus in the respiratory disease scenario of this host.
Highlights
The genus Pneumocystis comprises fungal species of opportunistic respiratory pathogens that are responsible for severe and potentially lethal pneumonia in immunocompromised humans and other mammals
With regard to respiratory diseases, the pig typically presents a poly-microbial and multifactorial scenario, which is commonly described with the term Porcine Respiratory Disease Complex (PRDC)
Despite a significant decrease in the P. suis infection rate in fattening pigs at the fourth month of life, the P. suis organism load remained comparable to that at the earlier stages. These results appear to be in line with a previous study, which reported the highest prevalence of P. suis in the post-weaning phase [26] or the highest organism load in two-month-old piglets as determined by qPCR [29]
Summary
The genus Pneumocystis comprises fungal species of opportunistic respiratory pathogens that are responsible for severe and potentially lethal pneumonia in immunocompromised humans and other mammals. This variation was observed in our annual routine diagnostics data (Blasi, unpublished data) It is currently not completely clear whether the fungus causes a subclinical infection or is rather a true pulmonary pathogen in pigs, as a P. suis single-infection has been rarely reported, especially in relation to specific clinical symptoms. Diagnostic studies in P. suis-positive specimens consistently revealed co-infections with other pulmonary pathogens including Porcine Circovirus type 2 (PCV2), PRRSV, Pasteurella multocida, Streptococcus suis, and Mycoplasma hyopneumoniae [14,26]. We sampled bronchoalveolar lavage fluid (BALF) and serum of pigs from five different farms at five time points and quantified P. suis and other pulmonary pathogens including PCV2, PRRSV, Swine Influenza Virus (SIV), Actinobacillus pleuropneumoniae (A.p.), Bordetella bronchiseptica (B.b.), Bordetella pertussis (B.pe.), Bordetella parapertussis (B.pa.), Mycoplasma hyopneumoniae (M.hp.), Mycoplasma hyorhinis (M.hr.), Mycoplasma flocculare (M.fl), Pasteurella multocida (P.m.), Glaesserella parasuis (G.p.), and Streptococcus suis (S.s.). Clinical symptoms of each pig were documented at every time point and analyzed for any correlations with the types and quantities of pulmonary pathogens detected
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