Immunohistochemical study of Pneumocystis carinii infection in pigs: evaluation of Pneumocystis pneumonia and a retrospective investigation

Meta-Analysis and Systematic Literature Review of the Genus Pneumocystis in Pet, Farm, Zoo, and Wild Mammal Species

A systematic literature search on Pneumocystis in 276 pet, farm, zoo, and wild mammal species resulted in 124 publications originating from 38 countries that were analyzed descriptively and statistically, for which inclusion and exclusion criteria were exactly defined. The range of recorded Pneumocystis prevalence was broad, yet in half of the citations a prevalence of ≤25% was documented. Prevalence was significantly dependent on the method used for Pneumocystis detection, with PCR revealing the highest percentages. Pet animals showed the lowest median Pneumocystis prevalence, followed by farm, wild, and zoo animals. In contrast, pet and farm animals showed higher proportions of high-grade infection levels compared to zoo and wild mammals. Only in individual cases, all of them associated with severe Pneumocystis pneumonia, was an underlying immunosuppression confirmed. Acquired immunosuppression caused by other diseases was frequently discussed, but its significance, especially in highly immunosuppressive cases, needs to be clarified. This meta-analysis supported a potential influence of the social and environmental factors of the host on Pneumocystis transmission in wildlife, which must be further elucidated, as well as the genetic diversity of the fungus.

Pneumocystis spp. in Pigs: A Longitudinal Quantitative Study and Co-Infection Assessment in Austrian Farms

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.

Disseminated Pneumocystosis in a Toy Poodle

A 1-year and 7-months-old neutered male toy poodle was presented with persistent respiratory distress, gradual weight loss and melaena. Thoracic radiography showed an unstructured interstitial lung pattern. Histopathological examination of tissues collected at necropsy examination revealed disseminated infection by Pneumocystis carinii. The organisms were detected in the lungs, lymph nodes, liver, heart, kidneys, spleen, gastrointestinal tract and pancreas. In the lungs, the organisms were present in the alveolar space and interstitial tissue, and calcified foci containing P. carinii were observed. The presence of the organism in non-thoracic lymph nodes provided evidence of lymphogenous spread. A definitive diagnosis of disseminated pneumocystosis was achieved through the use of Grocott methenamine silver staining, immunohistochemistry (IHC) and polymerase chain reaction for P. carinii. Depletion of cells expressing immunoglobulin (Ig)A and IgG was confirmed by IHC of lymphoid tissue, suggesting possible underlying immunodeficiency.

Common variable immune deficiency in a Pomeranian with Pneumocystis carinii pneumonia

A Pomeranian dog, 1 year- and 8 month-old neutered female, was presented with persistent respiratory distress and recurrent generalized demodicosis. Physical examination revealed cyanosis, rough respiratory sounds, multifocal alopecia and dermal erosions on the dorsal side of the forelimbs, perineal area and skin around the eyes. A severe diffuse interstitial lung pattern was observed on thoracic radiographs. The blood examination revealed neutrophilia and hypoglobulinemia. Serum immunoglobulin concentrations of IgG and IgA were low. Histopathological examination revealed severe diffuse interstitial pneumonia with Pneumocystis carinii infection. Severe lymphoid depletion was observed in the spleen and other organs with lymphoid follicles consisted mainly of CD3-positive T cells and few cells of B-cell lineage. B-cell hypoplasia with subsequent antibody deficiency was suspected.

Detection of Pneumocystis infections by in situ hybridization in lung samples of Austrian pigs with interstitial pneumonia

Pneumocystis carinii f. sp. suis is a fungus multiplying in the respiratory tract of pigs which occasionally is associated with interstitial pneumonia. Identification of Pneumocystis in tissue samples is considered difficult and there are only scarce data on its occurrence in European pigs. This investigation presents an in situ hybridization (ISH) procedure for identification of Pneumocystis spp. in paraffin wax embedded tissue samples and its application for labeling the agent in lung samples of pigs with interstitial pneumonia. Thirty-two out of 100 lung samples from pigs on Austrian farms were identified as positive, five of them with multiple, 12 with moderate and 15 with few organisms but Grocott’s methenamine silver staining demonstrated that only 20 cases were unequivocally positive for Pneumocystis carinii. In addition to interstitial pneumonia Pneumocystis-positive pigs were more frequently affected with granulomatous pneumonia than Pneumocystis-negative pigs. Frequently concurrent infections with different viral or bacterial lung pathogens were noted but there was no positive correlation between Pneumocystis- and PCV-2-infections. With other infections, no clear-cut differences between Pneumocystis-positive and Pneumocystis-negative animals were found. This study shows that Pneumocystis infections occur frequently in Austrian pigs with interstitial pneumonia. It remains to be shown which are the factors triggering severe multiplication and whether infection with Pneumocystis alone is able to induce lung disease in pigs.

Characterizing Pneumocystis in the lungs of bats: understanding Pneumocystis evolution and the spread of Pneumocystis organisms in mammal populations

Bats belong to a wide variety of species and occupy diversified habitats, from cities to the countryside. Their different diets (i.e., nectarivore, frugivore, insectivore, hematophage) lead Chiroptera to colonize a range of ecological niches. These flying mammals exert an undisputable impact on both ecosystems and circulation of pathogens that they harbor. Pneumocystis species are recognized as major opportunistic fungal pathogens which cause life-threatening pneumonia in severely immunocompromised or weakened mammals. Pneumocystis consists of a heterogeneous group of highly adapted host-specific fungal parasites that colonize a wide range of mammalian hosts. In the present study, 216 lungs of 19 bat species, sampled from diverse biotopes in the New and Old Worlds, were examined. Each bat species may be harboring a specific Pneumocystis species. We report 32.9% of Pneumocystis carriage in wild bats (41.9% in Microchiroptera). Ecological and behavioral factors (elevation, crowding, migration) seemed to influence the Pneumocystis carriage. This study suggests that Pneumocystis-host association may yield much information on Pneumocystis transmission, phylogeny, and biology in mammals. Moreover, the link between genetic variability of Pneumocystis isolated from populations of the same bat species and their geographic area could be exploited in terms of phylogeography.

Study of the epidemiology of Pneumocystis carinii f. sp. suis in abattoir swine in Portugal

Pneumocystis has been identified in various mammalian species, including domestic, wild and zoo animals. This study's main objectives were: (1) to estimate the prevalence of the Pneumocystis carinii f. sp. suis infection in slaughtered pigs in Portugal, (2) assess the prevalence differences within distinct age groups of animals, (3) determine the possible associations between pulmonary lesions and the infection, and (4) genetically characterize the P. carinii f. sp. suis isolates recovered from infected animals using PCR with DNA sequencing. An epidemiological cross-sectional study was conducted using 215 pig lung tissue samples which demonstrated a global prevalence of 7% (14 positive samples). This value was later validated by statistical analysis as being representative of the national population prevalence. Regarding the assessment of relations between the different variables investigated during the study (age, gender, geographical region, type of farming, weight and pulmonary lesion) and the P. carinii f. sp. suis infection, no significant statistical differences were found, and apparently, no predisposing factors could be defined. Nevertheless, infection by Pneumocystis in pigs is ubiquitous and it can be detected in healthy animals. Thus, the colonization of P. carinii f. sp. suis among healthy individuals suggests that asymptomatic carriers can be an effective reservoir for susceptible animals and participate in the transmission of infection. The present data confirmed that porcine Pneumocystis is genetically distinct from Pneumocystis DNA detected in other mammalian hosts.

Epidemiological characteristics of pulmonary pneumocystosis and concurrent infections in pigs in Jeju Island, Korea

Epidemiological characteristics of swine pulmonary Pneumocystis (P.) carinii and concurrent infections were surveyed on Jeju Island, Korea, within a designated period in 172 pigs submitted from 54 farms to the Department of Veterinary Medicine, Jeju National University. The submitted cases were evaluated by histopathology, immunohistochemistry, PCR/RT-PCR, and bacteriology. P. carinii infection was confirmed in 39 (22.7%) of the 172 pigs. Histopathologically, the lungs had moderate to severe lymphohistioctyic interstitial pneumonia with variable numbers of fungal organisms within lesions. Furthermore, porcine reproductive and respiratory syndrome virus (PRRSV) and porcine circovirus type 2 (PCV-2) co-infection was a common phenomenon (12.8%, 20.5%, and 48.7% were positive for PRRS, PCV-2, or both, respectively, as determined by PCR/RT-PCR). Infection was much more concentrated during winter (December to March) and 53.8% of the infected pigs were 7- to 8-weeks old. In addition, three pigs showed co-infection with bacteria such as Pasteurella multocida and Streptococcus suis. The results of the present study suggest that the secondary P. carinii infection is common following primary viral infection in swine in Korea. They further suggest that co-infection of P. carinii might be enhanced by the virulence of primary pathogens or might have synergistic effects in the pigs with chronic wasting diseases.

Immunohistochemical and ultra-structural detection of Pneumocystis in wild boars (Sus scrofa) co-infected with porcine circovirus type 2 (PCV2) in Southern Brazil

Pneumocystis spp. are fungi that are able to infect a variety of host species and, occasionally, lead to severe pneumonia. Porcine circovirus type 2 (PCV2) is an important viral pathogen which affects both swine and wild boar herds worldwide. Co-infection between PCV2 and other pathogens has been reported, and the secondary immunodeficiency caused by the virus may predispose to these co-infections. In the present study, postmortem tissue samples obtained from wild boar herds in Southern Brazil were analyzed by histopathology, ultra-structural observation, and immunohistochemistry. Forty-seven out of seventy-eight (60%) wild boars showed clinical signs, gross, and histopathological lesions characteristic of infection by PCV2. Pneumocystis was detected by immunohistochemistry in 39 (50%) lungs and viral antigens of PCV2 were found in 29 (37.2%) samples. Concomitant presence of Pneumocystis and PCV2 were observed in 16 (20.5%) of the wild boars. Cystic and trophic forms of Pneumocystis were similar to previously described ultra-structural observations in other mammals.

Immune response to fungal infections

The immune mechanisms of defence against fungal infections are numerous, and range from protective mechanisms that were present early in evolution (innate immunity) to sophisticated adaptive mechanisms that are induced specifically during infection and disease (adaptive immunity). The first-line innate mechanism is the presence of physical barriers in the form of skin and mucous membranes, which is complemented by cell membranes, cellular receptors and humoral factors. There has been a debate about the relative contribution of humoral and cellular immunity to host defence against fungal infections. For a long time it was considered that cell-mediated immunity (CMI) was important, but humoral immunity had little or no role. However, it is accepted now that CMI is the main mechanism of defence, but that certain types of antibody response are protective. In general, Th1-type CMI is required for clearance of a fungal infection, while Th2 immunity usually results in susceptibility to infection. Aspergillosis, which is a disease caused by the fungus Aspergillus, has been the subject of many studies, including details of the immune response. Attempts to relate aspergillosis to some form of immunosuppression in animals, as is the case with humans, have not been successful to date. The defence against Aspergillus is based on recognition of the pathogen, a rapidly deployed and highly effective innate effector phase, and a delayed but robust adaptive effector phase. Candida albicans, part of the normal microbial flora associated with mucous surfaces, can be present as congenital candidiasis or as acquired defects of cell-mediated immunity. Resistance to this yeast is associated with Th1 CMI, whereas Th2 immunity is associated with susceptibility to systemic infection. Dermatophytes produce skin alterations in humans and other animals, and the essential role of the CMI response is to destroy the fungi and produce an immunoprotective status against re-infection. The resolution of the disease is associated with a delayed hypersensitive response. There are many effective veterinary vaccines against dermatophytoses. Malassezia pachydermatis is an opportunistic yeast that needs predisposing factors to cause disease, often related to an atopic status in the animal. Two species can be differentiated within the genus Cryptococcus with immunologic consequences: C. neoformans infects predominantly immunocompromised hosts, and C. gattii infects non-immunocompromised hosts. Pneumocystis is a fungus that infects only immunosupressed individuals, inducing a host defence mechanism similar to that induced by other fungal pathogens, such as Aspergillus.

Detection ofPneumocystisspp. in lung samples from pigs in Brazil

The genus Pneumocystis is composed of opportunistic fungi currently considered as specific pulmonary pathogens in humans and other mammals. In pigs, Pneumocystis pneumonia (PcP) could create significant economical losses due to its detrimental effects on growth, food conversion, and carcass/viscera condemnation. This study revealed that Pneumocystis organisms could be detected by Grocott's staining or immunohistochemistry in 36.9% of 564 slaughtered pigs from two geographic regions of Brazil. The prevalence of positive cases was 39.9% and 33.9% in pigs slaughtered in Rio Grande do Sul (RS) and Mato Grosso (MT) states, respectively. Among the positive cases in RS, Pneumocystis organisms were observed in 41.9% of 33 histologically normal lungs, and in 58.0% of lungs presenting with histological lesions. In contrast, the prevalence in MT in normal and abnormal lungs was 36.3% and 63.5%, respectively. Major histopathological findings in lungs of infected animals were bronchointerstitial pneumonia (47.6%), suggestive of enzootic pneumonia, and interstitial pneumonia (37.9%), compatible with PcP. The results of this survey strengthened the interest of detecting fungal pathogens, in addition to other infectious agents, and evaluating their financial impact on Brazilian pig industry. Preventive and/or therapeutic strategies should be developed in order to minimize the incidence of respiratory fungal infections in pigs and associated economic losses.

Molecular and serological evidence of Pneumocystis circulation in a social organization of healthy macaques (Macaca fascicularis)

Simian populations represent valuable models for understanding the epidemiology of human pneumocystosis. The present study aims to describe the circulation of Pneumocystis organisms within a social organization of healthy crab-eating macaques (Macaca fascicularis) living in a natural setting in France. Animals were followed for up to 2 years. Deep nasal swab and blood samples were collected monthly from each animal under general anaesthesia. Environmental air was sampled for a 1 week period every month in the park where the macaques dwelt. Pneumocystis DNA was detected by nested-PCR of mitochondrial large subunit rRNA (mtLSU) gene in nasal swab and air samples. Anti-Pneumocystis IgG antibodies were detected in serum samples by indirect immuno-fluorescence assay. Pneumocystis DNA was detected in 168 of 500 swab samples examined (33.6 %). The number of macaques with detectable Pneumocystis DNA was highly variable from one month to another. Positive detection of Pneumocystis DNA was not related to the detection of serum anti-Pneumocystis antibody. During the second year of the study, Pneumocystis DNA was amplified more frequently from unweaned macaques than from adults or subadults. The mtLSU sequence showed marked polymorphism with eight Pneumocystis sequence types representing two distinct groups. On the whole, a constant and intensive circulation of Pneumocystis organisms within the community was observed. However, the implication of the various members of the colony was probably different and several levels of colonization by Pneumocystis may occur in immunocompetent macaques.