Pythium insidiosum: an overview.

Pythiosis, lagenidiosis, and zygomycosis are devastating and often fatal infectious diseases that affect animals living in temperate, tropical, and sub- tropical climates throughout the world. The oomycete Pythium insidiosum and the zygomycetes Conidiobolus species and Basidiobolus species have been recognized as animal and human pathogens for many years. Members of the genus Lagenidium (a group of oomycetes closely related to the genus Pythium), however, have been identified as a cause of oomycosis in dogs only recently (1). Although they are caused by a phylogenetically diverse group of pathogens, pythiosis, lagenidiosis, and zygomycosis share similar clinical and histologic characteristics (all cause lesions characterized by pyogranuloma- tous and eosinophilic inflammation associated with broad, irregularly branching, sparsely septate hyphae), making them difficult to distinguish from one another. Because of these similarities, many veterinary pathologists and clinicians continue to use the inclusive but out-dated term ''phycomy- cosis'' when describing histologic or clinical findings that could be caused by any of these pathogens. Although this term is a convenient label for cases in which a definitive culture-based diagnosis has not been made, it is no longer an appropriate taxonomic designation, and it should be replaced with the more specific terms ''pythiosis,'' ''lagenidiosis,'' and ''zygomycosis.'' Clini- cally, distinguishing between these infections is important because of dif- ferences in epidemiology, choice and duration of therapy, and prognosis.

Pythiosis, lagenidiosis, and zygomycosis in small animals

Since its clinical introduction, computed tomography (CT) has revolutionized veterinary medicine and is considered to be one of the most valuable tools for the imaging work-up of neurological, oncological and orthopaedic canine and feline patients. In small animals with acute trauma, particularly those involving complex anatomic areas such as the head, spine or pelvis, CT has been established as a standard imaging method. With the increasing availability of radiation therapy in veterinary medicine, CT has also become the principal tool to stage a tumour, assess response, and guide radiation therapy. The increasing availability of helical CT in veterinary medicine has allowed novel techniques such as spiral CT angiography and high-resolution CT. This review provides a brief overview of the historical and technical development of CT and literature reviews of the major clinical CT applications in small animals such as intracranial and extracranial lesions, the spine, the appendicular skeleton, and abdominal and thoracic diseases.

Computed tomography in small animals--basic principles and state of the art applications.

Although infections caused by the straminipilan pathogen Pythium insidiosum were described in 19th century, it has been only recently that its epidemiology, immunology, treatment and other important traits were extensively studied. These studies were of paramount importance to theorize about the ecological niche for this pathogen, its host-parasite relationships, the antigens used for diagnosis, and the management of the infection using immunotherapy. P. insidiosum triggers in the infected host a T helper 2 [Th2] subset with an inflammatory reaction composed mainly of eosinophils and mast cells. These cells degranulate around the hyphal elements of P. insidiosum where a Splendore-Hoeppli-like reaction develops. In horses this reaction is so intensive that firm concretions called 'kunkers' develop. These data indicated that this pathogen might have developed an evolutionary strategy to conceal important antigens from the host immune system. Immunotherapy, a treatment approach that relies on the injection of antigens of P. insidiosum from in vitro cultures, has been successfully used in humans and horses to manage this disease. A switch from a Th2 to Th1 response is postulated as the most likely explanation of the curative properties of this approach. This review provides details on the serological, immunological, and immunotherapeutic methodologies used to diagnose and treat the infections caused by this pathogen.

Immunology and immunotherapy of the infections caused by Pythium insidiosum

Pythium insidiosum is an important cause of cutaneous and gastrointestinal disease in horses and dogs in the southeastern United States. Culture-based diagnosis of pythiosis is rarely definitive because production and identification of reproductive structures is difficult. The purpose of this study was to develop a polymerase chain reaction (PCR)-based assay for the identification of P insidiosum. Genomic DNA was extracted from 3 clinical isolates of P insidiosum and 1 isolate each of Pythium graminicola and Pythium arrhenomanes. The ITS 1 region of the ribosomal RNA gene of each isolate was amplified and sequenced, and the resultant sequences were aligned with published sequences for Pythium aphanidermatum, P acanthicum, and P myriotylum. A pair of P insidiosum— specific primers (PI-1 and PI-2) were designed from variable regions within the ITS1 region. A nested PCR assay was developed in which the 1st round amplified the ITS 1 region by use of universal fungal primers. Second-round amplification utilized the internal P insidiosum-specific primers PI-1 and PI-2. Specificity of the assay was tested with DNA extracted from cultures of the following: 10 clinical isolates of P insidiosum and 1 isolate each of P graminicola, P irregulare, P arrhenomanes, P myriotylum, P deliense, Basidiobolus ranarum, Conidiobolus coronatus, Aspergillus terreus, Lagenidium giganteum, and a canine-pathogenic Lagenidium species. Nested PCR produced a single 105-base pair amplicon for each of the P insidiosum isolates, but did not produce amplicons for any of the other isolates. Results of this study suggest that PCR is a useful tool for the identification of P insidiosum.

Development of a nested polymerase chain reaction assay for the detection and identification of Pythium insidiosum.

Nasal and retrobulbar infection caused by the Oomycete Pythium insidiosum is described in a cat. The diagnosis was established on three criteria. The staining of broad, sparsely septate hyphal elements in biopsy tissue using a fluorescein-labelled antiglobulin specific for P. insidiosum, detection of antibodies to P. insidiosum by an immunodiffusion test, and isolation of the aetiological agent in pure culture from the biopsy tissue. Treatment with ketoconazole for 6 weeks resulted in clinical improvement, but proptosis of the left eye slowly appeared after the discontinuation of treatment. This case represents a new host for P. insidiosum, namely, a domestic, shorthaired cat, from North Carolina, U.S.A.

Nasal and retrobulbar mass in a cat caused by Pythium insidiosum.

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Nasal and retrobulbar mass in a cat caused by Pythium insidiosum.