Pneumonia in a Paso-Fino mare

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.

Molecular diagnosis of Pneumocystis pneumonia in dogs

Pneumocystis pneumonia (PCP) is a life-threatening fungal disease that can occur in dogs. The aim of this study was to provide a preliminary genetic characterisation of Pneumocystis carinii f.sp.'canis' (P. canis) in dogs and thereby develop a reliable molecular protocol to definitively diagnose canine PCP. We investigated P. canis in a variety of lung specimens from dogs with confirmed or strongly suspected PCP (Group 1, n = 16), dogs with non-PCP lower respiratory tract problems (Group 2, n = 65) and dogs not suspected of having PCP or other lower respiratory diseases (Group 3, n = 11). Presence of Pneumocystis DNA was determined by nested PCR of the large and small mitochondrial subunit rRNA loci and by a real-time quantitative polymerase chain reaction (qPCR) assay developed using a new set of primers. Molecular results were correlated with the presence of Pneumocystis morphotypes detected in cytological/histological preparations. Pneumocystis DNA was amplified from 13/16 PCP-suspected dogs (Group 1) and from 4/76 dogs of control Groups 2 and 3 (combined). The latter four dogs were thought to have been colonized by P. canis. Comparison of CT values in 'infected' versus 'colonized' dogs was consistent with this notion, with a distinct difference in molecular burden between groups (CT ≤ 26 versus CT range (26 <CT < 35), respectively). Phylogenetic analyses showed that P. canis is specifically 'canine' associated, being separated from other mammalian Pneumocystis species, thereby confirming the accuracy of qPCR amplicon for Pneumocystis in dogs. Using qPCR, Pneumocystis DNA can be detected in specimens from the respiratory tract and a CT value can be interpreted to distinguish infection versus colonization.

Update on fungal respiratory disease in horses

Fungal respiratory disease is a rare occurrence in horses. Fungal organisms are ubiquitous in the equine environment; however, there is a geographic predisposition for disease development, with fungal respiratory infections seen more commonly by practitioners working in tropical or subtropical environments. Diagnosis and treatment of fungal respiratory infections pose a challenge for the equine practitioner, and the prognosis for complete resolution of infection is often guarded; however, new antifungal medications are likely to improve treatment success. This article summarizes the available literature regarding the cause, diagnosis, and treatment of equine fungal respiratory disease.

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.