Pneumocystis carinii infection with severe pneumomediastinum and lymph node involvement in a Whippet mixed-breed dog

Retracing the evolution of Pneumocystis species, with a focus on the human pathogen Pneumocystis jirovecii

SUMMARYEvery human being is presumed to be infected by the fungus Pneumocystis jirovecii at least once in his or her lifetime. This fungus belongs to a large group of species that appear to exclusively infect mammals, with P. jirovecii being the only one known to cause disease in humans. The mystery of P. jirovecii origin and speciation is just beginning to unravel. Here, we provide a review of the major steps of P. jirovecii evolution. The Pneumocystis genus likely originated from soil or plant-associated organisms during the period of Cretaceous ~165 million years ago and successfully shifted to mammals. The transition coincided with a substantial loss of genes, many of which are related to the synthesis of nutrients that can be scavenged from hosts or cell wall components that could be targeted by the mammalian immune system. Following the transition, the Pneumocystis genus cospeciated with mammals. Each species specialized at infecting its own host. Host specialization is presumably built at least partially upon surface glycoproteins, whose protogene was acquired prior to the genus formation. P. jirovecii appeared at ~65 million years ago, overlapping with the emergence of the first primates. P. jirovecii and its sister species P. macacae, which infects macaques nowadays, may have had overlapping host ranges in the distant past. Clues from molecular clocks suggest that P. jirovecii did not cospeciate with humans. Molecular evidence suggests that Pneumocystis speciation involved chromosomal rearrangements and the mounting of genetic barriers that inhibit gene flow among species.

Spontaneous pulmonary interstitial emphysema, pneumomediastinum and cervical subcutaneous emphysema secondary to the Macklin effect in dogs with no clinical signs: 12 cases

Pneumomediastinum denotes the presence of gas within the mediastinum and generally occurs by leakage of air from an aerated viscus that traverses or abuts the mediastinal plane. The Macklin effect has been described in several veterinary studies and describes gas tracking along the perivascular interstitium following alveolar rupture causing interstitial emphysema, pneumomediastinum and subsequently cervical subcutaneous emphysema. This retrospective case series describes incidental spontaneous pulmonary interstitial emphysema, pneumomediastinum and cervical subcutaneous emphysema secondary to the Macklin effect in dogs with no related clinical signs. Twelve dogs were identified from the author's institution, of which 75 % were Sighthounds (Greyhounds, Whippets or Lurchers). Pulmonary interstitial emphysema had a predominantly paravascular distribution, although in some cases a parabronchial distribution was also identified. We conclude that incidental pulmonary interstitial emphysema, pneumomediastinum and secondary cervical subcutaneous emphysema can be incidental, presumed secondary to the Macklin effect and that Sighthound breeds may be overrepresented.

Development of Highly Efficient Universal Pneumocystis Primers and Their Application in Investigating the Prevalence and Genetic Diversity of Pneumocystis in Wild Hares and Rabbits

Despite its ubiquitous infectivity to mammals with strong host specificity, our current knowledge about Pneumocystis has originated from studies of merely 4% of extant mammalian species. Further studies of Pneumocystis epidemiology across a broader range of animal species require the use of assays with high sensitivity and specificity. To this end, we have developed multiple universal Pneumocystis primers targeting different genetic loci with high amplification efficiency. Application of these primers to PCR investigation of Pneumocystis in free-living hares (Lepus townsendii, n = 130) and rabbits (Oryctolagus cuniculus, n = 8) in Canada revealed a prevalence of 81% (105/130) and 25% (2/8), respectively. Genotyping analysis identified five and two variants of Pneumocystis from hares and rabbits, respectively, with significant sequence divergence between the variants from hares. Based on phylogenetic analysis using nearly full-length sequences of the mitochondrial genome, nuclear rRNA operon and dihydropteroate synthase gene for the two most common variants, Pneumocystis in hares and rabbits are more closely related to each other than either are to Pneumocystis in other mammals. Furthermore, Pneumocystis in both hares and rabbits are more closely related to Pneumocystis in primates and dogs than to Pneumocystis in rodents. The high prevalence of Pneumocystis in hares (P. sp. 'townsendii') suggests its widespread transmissibility in the natural environment, similar to P. oryctolagi in rabbits. The presence of multiple distinct Pneumocystis populations in hares contrasts with the lack of apparent intra-species heterogeneity in P. oryctolagi, implying a unique evolution history of P. sp. 'townsendii' in hares.

Air leak syndrome in animals: definition and pathogenesis

Air leak syndrome (ALS) is described in human medicine as a constellation of clinical disorders including pneumomediastinum, pneumopericardium, pulmonary interstitial emphysema, pneumothorax, pneumoperitoneum, pneumoretroperitoneum and subcutaneous emphysema. The pathogenesis of ALS depends on the anatomy of the mediastinum and its associations with thoracic, abdominal and cervical connective tissues, as well as a physical phenomenon referred to as the Macklin effect. Various animal species develop diverse combinations of these lesions, although ALS has not been recognized in animals. However, this term aids pathologists in addressing this disease compilation. The aim of this retrospective study is to illustrate examples of ALS in animals by arbitrarily selecting 13 cases in dogs, cats, pinnipeds, sea otters and harbour porpoises. ALS can be classified into three groups based on aetiology: iatrogenic, secondary or spontaneous. Iatrogenic ALS was diagnosed in two cats with tracheal laceration following endotracheal intubation. Secondary ALS was identified in two dogs, one with acute respiratory distress syndrome and the other due to grass awn migration. Secondary ALS in pinnipeds was diagnosed following severe pulmonary parasitism, uraemic pneumonia and oesophageal perforation. The other marine mammals developed ALS following trauma. Spontaneous ALS was also diagnosed in one cat and one dog without any apparent predisposing causes.

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.

Oculosystemic pneumocystosis in 2 sibling Chihuahuas

Sibling female and male Chihuahuas were evaluated for a 9-month history of tachypnea that failed to respond to fenbendazole, doxycycline, amoxicillin-clavulanate, and prednisone. Physical examination identified tachypnea, hyperpnea, and harsh bronchovesicular lung sounds. Fundic examination disclosed diffuse chorioretinitis, manifested as multifocal chorioretinal granulomas in the female dog and occasional chorioretinal scars in the male dog. Thoracic radiographs indicated moderate to severe interstitial to broncho-interstitial infiltrates in both dogs. Serum and urine antigen and antibody testing in the female dog failed to identify infectious agents, but cytologic assessment of hepatic lymph node, liver, and splenic aspirates identified Pneumocystis trophozoites. Infection was confirmed in both dogs by 28S rRNA PCR sequencing from multiple tissue samples. The female dog responded well to trimethoprim-sulfamethoxazole, but the male dog was euthanized because of liver failure, presumably related to antimicrobial treatment.

Detection of Pneumocystis and Morphological Description of Fungal Distribution and Severity of Infection in Thirty-Six Mammal Species

Pneumocystis spp. are thought to adapt to the lungs of potentially all mammals. However, the full host range, fungal burden and severity of infection are unknown for many species. In this study, lung tissue samples originating from 845 animals of 31 different families of eight mammal orders were screened by in situ hybridization (ISH) using a universal 18S rRNA probe for Pneumocystis, followed by hematoxylin and eosin (H&E) staining for determining histopathological lesions. A total of 216 (26%) samples were positive for Pneumocystis spp., encompassing 36 of 98 investigated mammal species, with 17 of them being described for the first time for the presence of Pneumocystis spp. The prevalence of Pneumocystis spp. as assessed by ISH varied greatly among different mammal species while the organism load was overall low, suggesting a status of colonization or subclinical infection. Severe Pneumocystis pneumonia seemed to be very rare. For most of the Pneumocystis-positive samples, comparative microscopic examination of H&E- and ISH-stained serial sections revealed an association of the fungus with minor lesions, consistent with an interstitial pneumonia. Colonization or subclinical infection of Pneumocystis in the lung might be important in many mammal species because the animals may serve as a reservoir.

First Molecular Detection of Pneumocystis spp. in the Golden Jackal (Canis aureus)

Forty-six golden jackals (Canis aureus) were collected between November 2020 and February 2021 in five counties of Serbia. Lung samples were screened for the presence of Pneumocystis DNA by pan-Pneumocystis PCR on the mtLSU rRNA gene obtaining PCR products of 370 bp in length. Pneumocystis DNA was detected in the lungs from 6/46 (13.04%) golden jackals. Four were females and two were males; four were classified as adults and two as subadults. Positive samples were confirmed in 4/5 investigated counties. No gross pathologic lung lesions were observed in this study. The sequences of Pneumocystis spp. from golden jackals were identical to one another and showed the highest similarity with Pneumocystis spp. sequences of dogs (98% nucleotide identity). The genetic variation was comparable to Pneumocystis spp. of raccoon dogs (95-97% nucleotide identity), red foxes (91-95% nucleotide identity), ferrets (86% nucleotide identity), and another Pneumocystis type in dogs (P. canis Ck2, 81% nucleotide identity) was higher. Golden jackals may be carriers and may play a nonnegligible role in the spread of Pneumocystis spp. Although this finding cannot be directly related to any clinical manifestation or pathologic lesions, a possible role in the exacerbation of different pulmonary disorders should be considered.

Pneumocystosis in a lurcher puppy

A 10-month-old lurcher with history of recurrent skin problems, presented with tachypnoea which had progressively become severe. Investigations included haematology, serum biochemistry, blood coagulation profile, diagnostic imaging, bronchoscopy and bronchoalveolar lavage (BAL). Cytological evaluation of the BAL revealed the presence of Pneumocystis cysts. The patient was euthanased on humane grounds prior to treatment against Pneumocystosis. To the best of our knowledge this is the first case of Pneumocystosis in a lurcher puppy.

Humans Are Selectively Exposed to Pneumocystis jirovecii

Environmental exposure has a significant impact on human health. While some airborne fungi can cause life-threatening infections, the impact of environment on fungal spore dispersal and transmission is poorly understood. The democratization of shotgun metagenomics allows us to explore important questions about fungal propagation. We focus on Pneumocystis, a genus of host-specific fungi that infect mammals via airborne particles. In humans, Pneumocystis jirovecii causes lethal infections in immunocompromised patients if untreated, although its environmental reservoir and transmission route remain unclear.

Environmental exposure has a significant impact on human health. While some airborne fungi can cause life-threatening infections, the impact of environment on fungal spore dispersal and transmission is poorly understood. The democratization of shotgun metagenomics allows us to explore important questions about fungal propagation. We focus on Pneumocystis, a genus of host-specific fungi that infect mammals via airborne particles. In humans, Pneumocystis jirovecii causes lethal infections in immunocompromised patients if untreated, although its environmental reservoir and transmission route remain unclear. Here, we attempt to clarify, by analyzing human exposome metagenomic data sets, whether humans are exposed to different Pneumocystis species present in the air but only P. jirovecii cells are able to replicate or whether they are selectively exposed to P. jirovecii. Our analysis supports the latter hypothesis, which is consistent with a local transmission model. These data also suggest that healthy carriers are a major driver for the transmission.

Diversity and Complexity of the Large Surface Protein Family in the Compacted Genomes of Multiple Pneumocystis Species

Pneumocystis, a major opportunistic pathogen in patients with a broad range of immunodeficiencies, contains abundant surface proteins encoded by a multicopy gene family, termed the major surface glycoprotein (Msg) gene superfamily. This superfamily has been identified in all Pneumocystis species characterized to date, highlighting its important role in Pneumocystis biology. In this report, through a comprehensive and in-depth characterization of 459 msg genes from 7 Pneumocystis species, we demonstrate, for the first time, the phylogeny and evolution of conserved domains in Msg proteins and provide a detailed description of the classification, unique characteristics, and phylogenetic relatedness of five Msg families. We further describe, for the first time, the relative expression levels of individual msg families in two rodent Pneumocystis species, the substantial variability of the msg repertoires in P. carinii from laboratory and wild rats, and the distinct features of the expression site for the classic msg genes in Pneumocystis from 8 mammalian host species. Our analysis suggests multiple functions for this superfamily rather than just conferring antigenic variation to allow immune evasion as previously believed. This study provides a rich source of information that lays the foundation for the continued experimental exploration of the functions of the Msg superfamily in Pneumocystis biology.IMPORTANCEPneumocystis continues to be a major cause of disease in humans with immunodeficiency, especially those with HIV/AIDS and organ transplants, and is being seen with increasing frequency worldwide in patients treated with immunodepleting monoclonal antibodies. Annual health care associated with Pneumocystis pneumonia costs ∼$475 million dollars in the United States alone. In addition to causing overt disease in immunodeficient individuals, Pneumocystis can cause subclinical infection or colonization in healthy individuals, which may play an important role in species preservation and disease transmission. Our work sheds new light on the diversity and complexity of the msg superfamily and strongly suggests that the versatility of this superfamily reflects multiple functions, including antigenic variation to allow immune evasion and optimal adaptation to host environmental conditions to promote efficient infection and transmission. These findings are essential to consider in developing new diagnostic and therapeutic strategies.

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.

Nested-polymerase chain reaction detection of Pneumocystis carinii f. sp. canis in a suspected immunocompromised Cavalier King Charles spaniel with multiple infections

A 7-month-old Cavalier King Charles Spaniel female was referred due to a chronic cough refractory to antibiotic treatments. Laboratory findings showed leukocytosis, increased serum C-reactive protein, hypogammaglobulinemia, and decreased total serum immunoglobulin G concentration. Thoracic radiographs showed a mild bronchial pattern. Cytology of the bronchoalveolar lavage fluid revealed a septic inflammation. Bordetella bronchiseptica, Mycoplasma spp., and Pneumocystis carinii were identified by polymerase chain reaction testing, and Klebsiella pneumonia was cultured from the bronchoalveolar lavage fluid. Moreover, Escherichia coli was also cultured from urine. Pneumocystis spp. identification was done by sequencing of genetic amplicons. The dog died due to cardiopulmonary arrest secondary to a spontaneous pneumothorax on the day following the procedure. This report documents the detection of Pneumocystis carinii f. sp. canis in a suspected immunocompromised Cavalier King Charles Spaniel with concurrent pulmonary and urinary tract infections involving four different pathogens, and highlights the importance of the use of polymerase chain reaction testing to detect canine Pneumocystis spp. in cases with negative bronchoalveolar lavage cytology.

CT findings in Pneumocystis carinii pneumonia in five dogs

Pneumocystis carinii pneumonia is a rare disease in dogs. It is primarily reported in cavalier King Charles spaniels and miniature dachshunds with suspected underlying immunodeficiency. This case series reports the findings in five dogs (four cavalier King Charles spaniels and one Bedlington terrier) with confirmed P. carinii pneumonia. Thoracic (CT) revealed ground glass opacity of the pulmonary parenchyma with a diffuse or multifocal distribution. The severity of this pattern was variable. Less consistent imaging findings included parenchymal bands, bronchial dilation and signs consistent with pulmonary hypertension. Four dogs recovered well with treatment and there was resolution of CT abnormalities in all dogs with follow-up.

Pneumocystosis in dogs: meta-analysis of 43 published cases including clinical signs, diagnostic procedures, and treatment

We evaluated 43 published cases of dogs with confirmed Pneumocystis infection regarding the value of clinical parameters indicating the presence of the disease as well as tools for the detection of the pathogen. The assessed parameters included clinical signs, laboratory findings, results of thoracic radiography, autopsy, histopathology, methods for the detection of Pneumocystis, as well as medical therapy. Pneumocystosis was diagnosed most often in certain breeds (Cavalier King Charles Spaniel, Miniature Dachshund) with a predisposition for impaired immunity. The median age of the dogs was 1 y. Chronic therapy-resistant respiratory signs, such as tachypnea, dyspnea, and cough, along with leukocytosis, neutrophilia, and hypogammaglobulinemia, were the most frequently described clinical and clinicopathologic abnormalities. Pneumocystosis can be masked by coinfections with other respiratory pathogens, and the successful detection of Pneumocystis organisms is of major relevance. Several detection methods have been used in the past, but only a few provide reliable results. In 2017, the cytologic evaluation of Giemsa-stained bronchoalveolar lavage samples is generally used, even if sensitivity is only moderate. More reliable results can be achieved using special stains or sensitive molecular techniques. Fast and reliable detection of Pneumocystis is the essential basis for appropriate treatment and higher survival chances for dogs.