Antigenic relationship between the animal and human pathogen Pythium insidiosum and nonpathogenic Pythium species

Recent update in diagnosis and treatment of human pythiosis

Human pythiosis is an infectious condition with high morbidity and mortality. The causative agent is the oomycete microorganism Pythium insidiosum. The pathogen inhabits ubiquitously in a wet environment, and direct exposure to the pathogen initiates the infection. Most patients with pythiosis require surgical removal of the affected organ, and many patients die from the disease. Awareness of pythiosis among healthcare personnel is increasing. In this review, we summarized and updated information on the diagnosis and treatment of human pythiosis. Vascular and ocular pythiosis are common clinical manifestations. Recognition of the typical clinical features of pythiosis is essential for early diagnosis. The definitive diagnosis of the disease requires laboratory testing, such as microbiological, serological, molecular, and proteomic assays. In vascular pythiosis, surgical intervention to achieve the organism-free margin of the affected tissue, in combination with the use of antifungal drugs and P. insidiosum immunotherapy, remains the recommended treatment. Ocular pythiosis is a serious condition and earliest therapeutic penetrating keratoplasty with wide surgical margin is the mainstay treatment. Thorough clinical assessment is essential in all patients to evaluate the treatment response and detect an early sign of the disease recurrence. In conclusion, early diagnosis and proper management are the keys to an optimal outcome of the patients with pythiosis.

Pythiosis in sheep from Paraná, southern Brazil

Abstract: This paper reports pythiosis in a sheep from southwestern Paraná, Brazil, confirmed by indirect ELISA (Enzime-Linked Immunosorbent Assay) and immunohistochemistry, as well as it describes the macro and microscopic injuries, in order to understand the pathogenicity. A 4-year-old ewe from a flock of 30 Santa Inês sheep, raised semi-extensively with access to a weir, showed cachexia, bilateral enlargement in nasal region, a serous and bloody secretion with a fetid odor from its nose and swollen submandibular and retropharyngeal lymph nodes. Blood collection was performed trough jugular vein puncture in order to make complete blood cell count (CBC) and to obtain serum for the subsequent serological examination. As the hematological counts were within the normal range for sheep, the animal was euthanized and submitted to necropsy. Indirect ELISA resulted positive for pythiosis. Necropsy revealed necrosis of the hard palate with a diameter of 3.5cm and extending up to the nasal cavity, forming a fistula. Submandibular and retropharyngeal lymph nodes were enlarged and edematous on section. Microscopic findings for submandibular and retropharyngeal lymph nodes consisted in moderate infiltration of eosinophils mainly in the subcapsular sinus, characterizing reactive eosinophilic lymphadenitis. The nasal cavity revealed rhinitis and oral cavity stomatitis with necro-eosinophilic and pronounced multifocal granulomatous infiltration and presence of hyphae. Hyphae found in palate and nasal cavity were positive for Pythium insidiosum by Grocott's method and immunohistochemistry, the last one considered to be confirmatory for the pathogen diagnostic. This report has an important epidemiological aspect, as it is the first case of pythiosis in sheep confirmed by serology in South Brazil and an alert of possible infection by the pathogen in floodplains.

Lagenidium sp. ocular infection mimicking ocular pythiosis

This is a report of a Lagenidium sp. in a Thai patient who was diagnosed with severe keratitis that was unresponsive to antibacterial and antifungal drugs. Examination of a corneal biopsy specimen confirmed the presence of aseptate hyphae. The internal transcribed spacer DNA sequence of the strain isolated showed 97% identity with Lagenidium giganteum and other Lagenidium species.

Immunodetection of fungal and oomycete pathogens: established and emerging threats to human health, animal welfare and global food security

Filamentous fungi (moulds), yeast-like fungi, and oomycetes cause life-threatening infections of humans and animals and are a major constraint to global food security, constituting a significant economic burden to both agriculture and medicine. As well as causing localized or systemic infections, certain species are potent producers of allergens and toxins that exacerbate respiratory diseases or cause cancer and organ damage. We review the pathogenic and toxigenic organisms that are etiologic agents of both animal and plant diseases or that have recently emerged as serious pathogens of immunocompromised individuals. The use of hybridoma and phage display technologies and their success in generating monoclonal antibodies for the detection and control of fungal and oomycete pathogens are explored. Monoclonal antibodies hold enormous potential for the development of rapid and specific tests for the diagnosis of human mycoses, however, unlike plant pathology, their use in medical mycology remains to be fully exploited.

Identification of Pythium insidiosum by nested PCR in cutaneous lesions of Brazilian horses and rabbits

Pythium insidiosum is a fungus-like organism present in subtropical and tropical areas, such as Brazil, known to infect humans and various animal species. P. insidiosum is the etiological agent of pythiosis, an emerging and granulomatous disease characterized mainly by cutaneous and subcutaneous lesions in horses, the principal species affected. Accurate diagnosis of pythiosis and identification of its causal agent by microbiological and serological tests can be often difficult and inconclusive principally for horses and humans. The aim of this study was to evaluate the application of the previously described P. insidiosum-specific nested polymerase chain reaction (PCR) assay to directly detect P. insidiosum DNA in clinical and experimental lesions. Universal fungal primers (ITS1 and ITS4) were used during the first-round of PCR to amplify ITS1, 5.8s, and ITS2. A second-round of PCR was conducted with P. insidiosum-specific primers (PI1 and PI2) to amplify a variable region within this ITS1. In this study, a total of 21 equine clinical samples (kunkers) and 28 specimens from experimentally infected rabbits were analyzed by nested PCR. The first-round of PCR generated 800-base pair products, and the second-round produced 105-base pair amplicons for each P. insidiosum-specific sample; no amplicons were generated in negative control samples. Our results suggest that nested PCR is an important and efficient tool for diagnosis of both endemic (horse samples) and experimental (rabbit samples) pythiosis.

Pythium insidiosum: an overview

Pythium insidiosum is an oomycete pathogenic in mammals. The infection occurs mainly in tropical and subtropical areas, particularly in horses, dogs and humans. Infection is acquired through small wounds via contact with water that contains motile zoospores or other propagules (zoospores or hyphae). The disease, though described as emerging has in fact already been described since 1884. Depending on the site of entry, infection can lead to different forms of pythiosis i.e. a cutaneous, vascular, ocular, gastrointestinal and a systemic form, which is rarely seen. The infection is not contagious; no animal-animal or animal-human transmission has been reported so far. Therapy includes radical surgery, antifungal drugs, immunotherapy or a combination of these therapies. The prevention to contract the disease in endemic areas is difficult. Avoiding stagnant waters could be of help, although the presence of P. insidiosum on grass and soil in enzootic areas renders this practice useless.

Antibodies in the sera of host species with pythiosis recognize a variety of unique immunogens in geographically divergent Pythium insidiosum strains

Studies by Western blot analyses have shown that antibodies in the sera of host species infected by Pythium insidiosum recognized several prominent proteins expressed by this fungus-like pathogen. Although these studies have utilized sera from infected patients and relevant local strains of P. insidiosum, the results are difficult to compare because of the lack of method standardization. In an effort to resolve this issue, we have utilized standardized methodologies to evaluate six P. insidiosum strains from Asia and the Americas and 15 serum samples from cattle, cats, dogs, horses, and humans with pythiosis from the same geographical regions. Our data show that the antibodies present in these sera recognize a wide variety of unique P. insidiosum immunogenic proteins. Although some of the prominent proteins in this study have been previously reported, several others have yet to be described. For instance, a approximately 28-kDa-molecular-mass antigen was detected by the antibodies in all serum samples evaluated. However, this antigen was strongly expressed by only one of the strains evaluated. A diffuse approximately 51-kDa protein was not detected by the antibodies in the human sera; but it was recognized by the antibodies in the sera of cattle, cats, dogs, and horses. This antigen was expressed by only two of the strains investigated. Several other similar examples were also observed. The variation of the P. insidiosum protein profile identified by the antibodies in the sera evaluated indicates that some geographically diverged P. insidosum strains expressed some unique immunogens in vitro and that during natural infection (in vivo) P. insidiosum might express a broader number of antigens variably detected by individuals within the same species but especially across species.

Emerging diseases in tropical dermatology

All dermatologists worldwide should have at least passing familiarity with various tropical maladies that generate cutaneous manifestions. In addition to the standard infectious ailments associated with tropical environs, the authors have described herein five "emerging" illnesses that are gaining increasing attention for their capacity to cause human disease in those immigrating from, or traveling to, the tropical and subtropical world.

Isolation and identification of the human pathogenPythium insidiosumfrom environmental samples collected in Thai agricultural areas

We describe the ecological niche of the human and animal pathogen Pythium insidiosum within endemic agricultural areas of Thailand. Samples were collected from irrigation water, including rice paddy fields, irrigation channels and reservoirs. Zoospores of P. insidiosum were captured from water by the use of a sterile human hair baiting technique. Pythium isolates were identified based on phenotypic characteristics and by using a specific PCR assay for P. insidiosum. In addition, internal transcribed spacer (ITS) regions of P. insidiosum rDNA were sequenced and used in the phylogenetic analysis of 20 other known P. insidiosum DNA sequences available in the database and 11 related DNA sequences of other Pythium species including Lagenidium giganteum. The sequences of 59 environmental isolates of Pythium spp. recovered from Thailand confirmed 99% identity to P. insidiosum. Three well supported phylogenetic groups within P. insidiosum were found. The protein profiles of P. insidiosum environmental strains were determined and compared with reference strains. A typical 45-30 kDa band was consistently found in all isolates of P. insidiosum but not in closely related Pythium species. This study provides the first evidence for the natural occurrence of P. insidiosum in endemic aquatic environments. The highest recovery rate of this hydrophilic pathogen was found to be from water reservoirs and our data show that irrigation water may be an important source of P. insidiosum infection for individuals working in endemic agricultural areas.

Mapping of Pythium insidiosum hyphal antigens and ultrastructural features using TEM

Pythium insidiosum, the aetiological agent of pythiosis, has been reported to cause disease in mammals. Although several aspects of this pathogen have been extensively investigated, its ultra-structural features and the location and characterization of the antigens expressed during infection have yet to be examined. During this study the ultrastructural characteristics and the mapping of P. insidiosum hyphal antigens from in vitro cultures were investigated. The ultrastructural study showed similarities between the hyphal features of this mammalian pathogen and other Pythium spp. Using immuno-electron microscopy and protein-A colloidal gold (PACG)-labelling, anti-P. insidiosum antibodies from the sera of infected hosts (bovine, canine, equine, feline, and human), were found to bind specifically to several cytoplasmic and cell wall antigens within the hyphae of P. insidiosum. The anti-P. insidiosum antibodies present in the sera from an infected feline showed only 85% gold binding, whereas the PACG particles failed to bind to the canine antibodies. The mapping of the hyphal antigens of P. insidiosum could be of importance for the specific selection of these antigens and their future molecular characterization. In addition, the antigens of P. insidiosum detected by sera from infected hosts could be used as purified antigens in the diagnosis and the immunotherapy of pythiosis.

Teste de ELISA indireto para o diagnóstico sorológico de pitiose

A pitiose, doença granulomatosa de eqüinos causada pelo oomiceto Pythium insidiosum, tem como característica a evolução rápida seguida de morte dos animais. Estas mortes muitas vezes são causadas por diagnósticos errôneos ou demorados quando os doentes já não respondem ao tratamento. Este trabalho teve por objetivo a padronização do ensaio imunoenzimático indireto (ELISA) para diagnóstico sorológico de pitiose em eqüinos e coelhos, visando a diminuição de erros e de tempo necessário para o diagnóstico. Para o desenvolvimento e validação do teste foram utilizadas 72 amostras de soro de eqüinos saudáveis e 44 soros de eqüinos com pitiose confirmada. Os resultados da validação do ELISA para eqüinos foram: sensibilidade 97,72%, especificidade 90,27%, valor preditivo positivo 86%, valor preditivo negativo 98,4% e eficiência de 93,1%. Para coelhos, o teste foi padronizado com 48 amostras de soro de animais saudáveis e 24 amostras de coelhos imunizados com antígenos de P. insidiosum. Os resultados foram: sensibilidade 91,66%, especificidade 95,83%, valor preditivo positivo 91,66%, valor preditivo negativo 95,83% e eficiência de 94,44%. Os resultados deste trabalho demonstram que o ensaio imunoenzimático indireto é um método seguro e eficaz para o diagnóstico sorológico da pitiose.

Immunology and immunotherapy of the infections caused by Pythium insidiosum

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.

Epizootic cutaneous pythiosis in beef calves

Enzootic bovine granulomatosis (EBG) is a disease that affects beef calves in the flooded Savanna regions of Venezuela. Although Pythium insidiosum was originally the suspected etiologic agent, nothing was done to demonstrate its presence in the infected animals. The objective of this study was to investigate the etiologic agent causing cutaneous lesions in a group of 63 calves diagnosed with EBG. The collected samples were analyzed by histopathology, immunohistochemistry, serology, and mycological techniques. The clinical manifestations of BEG included ulcerated and swollen granulomatous lesions on the limbs of young calves. Histopathological studies revealed an eosinophilic inflammatory reaction with neutrophils, giant cells and branching hyphae with the Splendore-Hoeppli phenomenon. Immunofluorescence analysis identified the branching hyphae as elements of the fungal-like organism P. insidiosum. Wet mounts in 10% KOH revealed hyaline slender branching hyaline coenocytic hyphae, but cultures from those samples were negative. Anti-P. insidiosum immunoglobulins were also demonstrated in the collected sera of the affected bovines using latex agglutination, immunodiffusion, ELISA, and Western Blot. The histopathological, immunohistochemical, and serological tests showed for the first time that P. insidiosum could be involved in epizootic bovine pythiosis.

Intestinal canine pythiosis in Venezuela confirmed by serological and sequencing analysis

An 11-months-old mixed Terrier male originally from Venezuela, was referred to a Veterinary Hospital with signs of depression, anorexia, vomiting and diarrhea. The illness had begun 1 month earlier. Despite antibiotic chemotherapy and vitamins, the disease progressed. Radiological exams showed involvement of the small intestine. Histopathological studies of tissue samples taken during surgical intervention revealed eosinophilic areas in the center of which, abundant eosinophils, histiocytes and giant cells were observed. Silver stained cross-sections of the small intestine showed slender sparsely septate hyphae within the necrotic areas. Attempts to isolate the etiologic agent in pure culture were fruitless. The dog died without a definitive diagnosis. Fixed tissue samples of the small intestine were later investigated using specific fluorescent antibodies for pythiosis and molecular tools. These exams indicated that the hyphae in the infected tissues belong to the straminipilan pathogen Pythium insidiosum. This is the first confirmed case of dog pythiosis in Venezuela.

Identification of emerging human-pathogenic Pythium insidiosum by serological and molecular assay-based methods

Pythium insidiosum is a pathogen that causes disease in both animals and humans. Human infection is rare; however, when it does occur, most patients, especially those having underlying hemoglobinopathy syndromes, such as thalassemia, exhibit a severe form. We identified four isolates of P. insidiosum. Two were recovered from tissue biopsy specimens from thalassemic and leukemic patients, one was derived from brain tissue from a thalassemic patient, and another was isolated from a corneal ulcer from a fourth patient. Western blotting and an enzyme-linked immunosorbent assay (ELISA) were performed with a serum sample derived from one thalassemic patient. The methods used to identify the P. insidiosum isolates were based on morphology, nucleic acid sequencing, and a PCR assay. To confirm the identification, portions of the 18S rRNA genes of these four isolates were sequenced. The sequences were shown to be homologous to previously described P. insidiosum DNA sequences. In addition, PCR amplification of the internal transcribed spacer region specific for P. insidiosum was positive for all four isolates. The ELISA with the serum sample from the thalassemic patient gave a positive result from a serum dilution of 1:800. Finally, Western immunoblotting with this serum sample showed positive immunoglobulin G recognition for proteins of 110, 73, 56, 42 to 35, 30 to 28, 26, and 23 kDa. The results of this study show that both molecularly based diagnostic and serodiagnostic techniques are useful for the rapid identification of human pythiosis. The predominant antigens recognized by Western blotting may be useful in the development of a more sensitive and specific diagnostic tool for this disease.

Pythium attrantheridium sp. nov.: taxonomy and comparison with related species

Pythium attrantheridium sp. nov. is a new species isolated from cavity spot lesions of carrots as well as apple and cherry seedlings from various locations widely distributed in Canada and the USA. This fungus is closely related to the heterothallic P. intermedium, but is distinguished by: (1) unique molecular characteristics; (2) unique morphological characteristics; and (3) mating incompatibility with P. intermedium. The ITS region of the nuclear rDNA of all strains of P. attrantheridium studied is different from that of all other known Pythium spp. The oogonia attract a large number of antheridia when compatible mating types contact each other. The positive mating type produces zoospores unlike those of P. intermedium. Thus, biological, morphological and molecular data support the recognition of a new species.

Development of a species-specific probe for Pythium insidiosum and the diagnosis of pythiosis

Pythium insidiosum, the only species in the genus that infects mammals, is the etiological agent of pythiosis, a granulomatous disease characterized by cutaneous and subcutaneous lesions and vascular diseases. Accurate diagnosis of pythiosis and identification of its causal agent are often inconsistent with current immunological diagnostic methods. A species-specific DNA probe was constructed by using a 530-bp HinfI fragment from the ribosomal DNA intergenic spacer of P. insidiosum. When the probe was incubated with dot blots of genomic DNA from 104 Pythium species, it hybridized only to the DNA of P. insidiosum and P. destruens-two species that have been considered conspecific. The probe also hybridized to DNA from 22 P. insidiosum isolates in this study, regardless of their geographic origin or animal host. When tested against genomic DNA from other pathogenic organisms (Aspergillus fumigatus, Basidiobolus ranarum, Conidiobolus coronatus, Lagenidium giganteum, Paracoccidioides brasiliensis, and Prototheca wickerhamii), no cross-hybridization of the probe was detected. The specificity of the probe to hybridize to genomic DNA from all isolates of P. insidiosum and not cross-react with DNA from other Pythium species or pathogens that cause symptoms similar to pythiosis in their hosts makes it a powerful tool for the accurate diagnosis of pythiosis. In addition, the probe has the potential for pathological and environmental diagnostic applications.

Disseminated pythiosis in three horses

Three cases of equine subcutaneous pythiosis with dissemination to the internal organs were investigated. The subcutaneous lesions were observed on the mammary gland, nostrils and limbs of the infected horses. Histopathological analysis of the infected tissues revealed a strong eosinophilic reaction, with macrophages, mast cells and giant cells. Sparsely septated hyphal filaments of 4-6 microm diameter were identified in the center of the eosinophilic areas. Specific fluorescent antibody against Pythium insidiosum confirmed the hyphae in the infected tissues in three examined horses. In one of the three cases, the DNA sequences amplified from the infected subcutaneous tissues and internal organs, revealed that P. insidiosum's 18S SSU rDNA amplicons shared 100% identity with those sequences deposit in GenBank. This is the first report confirming by immunochemical and genetic techniques that P. insidiosum can disseminated from superficial to deep structures.

Human pythiosis, a rare cause of arteritis: case report and literature review

OBJECTIVE

To present a case of Pythium insidiosum arteritis and review reported cases of human pythiosis.

METHODS

Search of MEDLINE (PubMed) and the Thai Index Medicus was performed using the words "pythiosis" and "pythium." Search of abstracts from a scientific meeting also was performed. Only reported cases in the English or Thai language, with enough clinical information for analysis, were included.

RESULTS

There were a total of 32 cases of human pythiosis, with 31 identified in the literature. Twenty-five cases were Thai. Twenty of 21 patients with known occupations were farmers. There was ocular infection in 9 cases, subcutaneous infection in 5 cases, arterial infection in 17 cases, and cardiopulmonary infection in 1 case. Thalassemia was a common associated finding. In addition to systemic antifungal therapy, surgery was required in most cases. The highest mortality rate was seen in the arteritic form, particularly in patients with arterial lesions proximal to the superficial femoral artery.

CONCLUSIONS

Human pythiosis is rare. Physicians should be suspicious of pythiosis in individuals, particularly farmers in Thailand, who develop nonhealing cutaneous ulcers or keratitis, which do not respond to conventional treatment. P insidiosum infections should be listed as a rare cause of infectious arteritis.

An improved Pythium insidiosum-vaccine formulation with enhanced immunotherapeutic properties in horses and dogs with pythiosis

The immunotherapeutic properties of a new Pythium insidiosum-vaccine formulation (PIV), was evaluated in 18 horses and 6 dogs with proven pythiosis from different enzootic areas in the United States. All injected horses but one responded with a weak (=29 mm, n=3), a mild (30-90 mm, n=7) or a strong (=100 mm, n=7) inflammatory reactions at the site of injection. Three equines with weak or negative reactions at the injection site were not cured. Seven equines with strong reactions at their injection sites, however, were cured. Six of the eight horses with mild reactions were also cured. The remaining two equines responded at first but both relapsed and finally died of their infections. The PIV cured only two of the six dogs used in this study. The new PIV formulation cured 72% of the equines (P=0.048) and 33% of the dogs with pythiosis. Dogs with chronic disease (greater than two months) did not responded to immunotherapy. The finding of eosinophils, mast cells, IgE and precipitin IgG during pythiosis suggested that a T helper 2 (Th2) subset is in place during this disease. In cured horses, the eosinophilic reaction was substituted by lymphocytes and mononuclear macrophages (Th1). This and previous studies strongly support the hypothesis that an immune-modulation from a Th2 to a Th1 subsets may be in part responsible for the PIV's curative properties.

A molecular phylogeny of Pythium insidiosum

Sequence analysis of the ribosomal DNA internal transcribed spacers (ITS) was used to establish phylogenetic relationships among 23 isolates of Pythium insidiosum, the etiological agent of pythiosis in mammals. The isolates were divided into three distinct clades that exhibited significant geographic isolation. Clade I consisted of isolates from North, Central, and South America, while clade II contained isolates from Asia and Australia. Also present in clade II was an isolate from a patient in the USA, but the origin of the infection may have been in the Middle East. Clade III was comprised of isolates from Thailand and the USA. All 23 P. insidiosum isolates were more closely related to each other than to any other Pythium species in this study. Additionally, all Pythium isolates formed a clade separate from both outgroup species, Phytophthora megasperma and Lagenidium giganteum. The ITS sequence results tend to support the existence of geographic variants or cryptic speciation within P. insidiosum. The sequence information obtained also provides an abundance of data for applications in the diagnosis of pythiosis and identification of P. insidiosum from clinical samples.

Duodenal obstruction caused by infection with Pythium insidiosum in a 12-week-old puppy

Pythium insidiosum is an aquatic fungus-like organism that causes a serious chronic granulomatous disease called pythiosis in animals and humans in tropical and subtropical regions of the world. In North America, pythiosis is most often diagnosed in the Gulf Coast states. Early recognition of the disease is crucial to successful treatment, which includes surgical resection of granulomatous lesions and administration of antifungal agents. Despite increasing availability of diagnostic tests, intestinal pythiosis is insidious and is often not detected until lesions are extensive. Intestinal pythiosis was diagnosed in a 12-week-old puppy from South Carolina examined because of vomiting, diarrhea, and anorexia. Pythiosis was not initially suspected because of the young age of the patient and because pythiosis is uncommon in this area.

Development and evaluation of an in-house enzyme-linked immunosorbent assay for early diagnosis and monitoring of human pythiosis

Human pythiosis is an emerging, fatal, infectious disease caused by Pythium insidiosum and occurs in both tropical and subtropical countries. Thalassemic patients, farmers, and aquatic-habitat residents are predisposed to this disease. Delayed treatment due to the long time required for isolation and identification of the causative organism, as well as the difficulty in obtaining internal organ specimens, results in high morbidity and mortality. To facilitate rapid diagnosis, an in-house enzyme-linked immunosorbent assay (ELISA) for the detection of immunoglobulin G antibodies against P. insidiosum was developed and evaluated for the diagnosis and monitoring of human pythiosis. Sixteen sera were collected from seven culture-proven human pythiosis cases. A total of 142 sera from thalassemic patients, from patients with other infectious diseases, and from healthy blood donors served as controls. All sera were tested in duplicate. By choosing a suitable cutoff point to maximize sensitivity and specificity, sera from pythiosis cases were all determined to be positive, whereas sera from control groups were all determined to be negative. ELISA signals from serial samples of sera taken from treated patients showed gradually declining levels of antibodies to P. insidiosum. The ELISA test was highly sensitive (100%) and specific (100%) and was useful for early diagnosis and for monitoring the treatment for pythiosis.

A description of cutaneous-subcutaneous pythiosis in fifteen dogs

Information regarding signalment, duration of clinical signs, history of swimming, results of CBC and serum biochemical analyses, biopsy findings and mycological results, together with treatments and outcome, was retrieved from the medical records of 15 dogs with a diagnosis of pythiosis made between 1985 and 1995 at the Colleges of Veterinary Medicine, North Carolina State University and the University of Florida. Most of the dogs were young (median age 22 months) and represented larger breeds (> 20 kg). Lesions were characteristically chronic, ulcerated, and nodular with multiple draining tracts on the limbs, thoracic wall or perineal regions. The median duration of these lesions was 3 months with a range of 2 weeks-6 months. Seven dogs had a history of swimming. Peripheral eosinophilia was observed in 14 of the dogs. Cytological evaluation of discharge, aspirates, or impression smears made from biopsy specimens revealed hyphae in five of 11 dogs (45%). Histopathological evaluation using the Gomori Methenamine-Silver (GMS) stain was the most useful test for providing presumptive evidence of cutaneous pythiosis. Immunotherapy or antifungal therapy using either amphotericin B, liposomal nystatin, itraconazole, or ketoconazole were all unsuccessful. The only dog to survive underwent amputation of the affected limb; thus, the prognosis for cutaneous pythiosis in the dog is poor.

Serodiagnosis of human and animal pythiosis using an enzyme-linked immunosorbent assay

Conventional serodiagnosis of Pythium insidiosum infections involves the use of the immunodiffusion (ID) test. This test specifically diagnoses human and animal pythiosis. The test, however, has limited sensitivity and does not detect some culturally proven cases of the disease. Because of the increased recognition of pythiosis among humans and animals, we developed and evaluated an enzyme-linked immunosorbent assay (ELISA) using a soluble antigen from broken hyphae of P. insidiosum. Studies were carried out with sera from five humans and eight animals with culturally and/or histologically proven pythiosis. Some of these sera were negative in the ID test for pythiosis. Heterologous case sera from thirteen humans and two horses, plus 5 sera from healthy humans and 17 from healthy animals, were tested. Of the pythiosis case sera tested, the ID test detected only 8 of 13 (61.5%), whereas the ELISA detected all of them (100%). The ID and ELISA tests were entirely specific and gave negative results or low titers respectively, with sera from humans and animals with heterologous fungal infections or with no apparent illness. No correlation was found between the height of the ELISA titers and negative or positive sera in the ID test. Our results indicate that the ELISA is a reliable serodiagnostic test for pythiosis. It is as specific as the ID test but more sensitive.

Pythium insidiosum keratitis

A case of Pythium insidiosum keratitis is described. It is an unusual organism that is difficult to isolate. Cases in animals and humans have been reported from tropical and subtropical parts of the world but this is the first case from a temperate region and was acquired from a hot pool. Although resembling a fungus, it is insensitive to all antifungals and requires wide surgical excision for cure.

Esophagitis due to Pythium insidiosum infection in two dogs

Chronic esophagitis due to Pythium insidiosum infection caused weight loss, dysphagia, and hypersalivation in 2 dogs from rural Tennessee. Although dog 1 presented for evaluation in December 1984 and dog 2 in October 1992, infection likely occurred during the previous summer by drinking fresh pond water containing zoospores. Hematologic testing revealed eosinophilia and hypergammaglobulinemia in one dog. An etiologic diagnosis was not made until postmortem evaluation when hyphae within necrotic and granulomatous cellular infiltrates in the esophageal wall were identified as P insidiosum by immunoperoxidase staining. Failure to culture the organism from the esophageal wall in dog 2 was attributed to refrigeration of the tissues, since refrigeration decreases the survivability of P insidiosum.

Cutaneous pythiosis in the horse

Pythiosis of horses in an invasive, ulcerative, proliferative, pyogranulomatous disease of the skin and subcutis caused by Pythium insidiosum, a fungus-like oomycete in the order Peronosporales of the kingdom Protista. Pythiosis is a form of "phycomycosis," which is a complex of pyogranulomatous diseases that also includes conidiobolomysosis, basidiobolobysosis, and disorders caused by members of the order Mucorales.

Occupational sensitization to Plasmopara viticola

Molds of the class of Oomycetes are of allergologic importance in special cases. However, probes are not commercially available for diagnostic purposes. Our case report is based on the medical history of a greenhouse worker who had atopic syndrome. He handled pure cultures of defined fungi and plants. A sensitization to pseudo mildew growing on grapevine (Plasmopara viticola) was found. Skin prick test and histamine release test results were positive when extract of P. viticola was used. Detection of IgE reactivities against pseudo mildew via binding tests, Western blot analysis, and isoelectric focusing immunoblot confirmed the diagnosis. To our knowledge these results demonstrate for the second time a sensitization to Oomycetes.

Life cycle of the human and animal oomycete pathogen Pythium insidiosum

Pythium insidiosum, the etiologic agent of pythiosis insidiosii, causes life-threatening infections in humans and animals. Previous studies of the epidemiology of this disease hypothesized about the possible life cycle of this oomycete. Details, however, were not provided on the steps required to cause infection. We investigated the life cycle of P. insidiosum by inoculating pieces of equine skin and plant leaves and then studying the ensuing events with a scanning electron microscope. Our observations revealed that zoospores had a strong tropism for skin tissue, horse and human hair, and water lily and grass leaves and a weak attraction to a variety of other leaves. Encysted zoospores were observed on the favored leaves and skin. There they produced germ tubes and later abundant hyphal filaments that penetrated leaf tissues. Young sporangia had compact, thick walls. The sporangial wall was reduced to a fragile membrane when the sporangia had produced well-differentiated biflagellate zoospores. The encysted zoospores secreted an amorphous material that permitted the zoospores to adhere to skin and plant tissues. On the basis of these findings, a model to explain the life cycle of P. insidiosum is proposed.

Human subcutaneous pythiosis

Two cases of subcutaneous infection caused by the primitive aquatic hyphal organism Pythium are described. Pythium is an important pathogen of horses in the U.S.A. and Australia. Cases of human subcutaneous pythiosis have been cited in the literature, but clinical and histopathological features have not been described previously. Both cases occurred in young immunocompetent males in the periorbital region and showed rapid growth, clinically mimicking a tumor and requiring operative biopsy. In both cases there was a history of exposure to either swampy water or horses. The tissue reaction was distinctive, closely resembling that seen in equine pythiosis, comprising well-defined granular eosinophilic islands bordered by macrophages, multinucleate giant cells, fibrosis and numerous eosinophils. Hyphae were well demonstrated with the Grocott stain but only poorly with the PAS method. Identity of the organisms was confirmed with an immunoperoxidase technique employing a polyclonal antiserum to Pythium. Both patients responded well to amphotericin B.

Fatal arteritis due to Pythium insidiosum infection in patients with thalassaemia

Six thalassaemic patients had a distinct clinical syndrome characterized by progressive ischemia of the lower extremities, with ascending arteritis and thrombosis of the main arteries of the lower limbs. With periodic acid Schiff and Gomori's methenamine silver staining a large number of hyphae were revealed in the arterial wall and the outer part of the thrombus. Pythium insidiosum was isolated from 3 patients. The clinical course of the disease was progressive gangrene of the extremities and the patients invariably died when the infectious process reached the bifurcation of the aorta. There is no effective antimicrobial agent for the syndrome and radical amputation was the only method to ensure survival of the patients. P. insidiosum infection should be considered in thalassaemic patients with leg ulcers or arterial occlusion of the lower limbs.

Immunoblot analysis of the humoral immune response to Pythium insidiosum in horses with pythiosis

Reactions to Pythium insidiosum by sera from horses with active pythiosis were investigated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblotting. Five strains of P. insidiosum were grown in nutrient broth and then sonicated. After centrifugation, supernatant antigens were separated by SDS-PAGE. An exoantigen of Conidiobolus coronatus was also tested. Bands with molecular weights between 97,000 and 14,000 were identified by Coomassie blue and silver staining. After being transferred to nitrocellulose, the antigens were reacted against sera from six horses with pythiosis, sera from four horses cured a year earlier by vaccination, and sera from five healthy horses. The sera from horses with pythiosis recognized at least 20 antigens in all strains. Three antigens with molecular weights of 32,000, 30,000, and 28,000 appeared to be immunodominant and specific. Sera from horses cured by immunotherapy showed only five very weak bands, three of them the 32,000-molecular-weight (32K), 30K, and 28K antigens. No bands were observed with sera from healthy horses or sera from horses with a variety of other infections. Sera from horses with pythiosis cross-reacted with the 44K antigen of C. coronatus. The immunodominant antigens described here may be useful for diagnostic purposes and in immunotherapy for this oomycotic infection in horses.

Evaluation of two vaccines for the treatment of pythiosis insidiosi in horses

Two vaccines to treat phythiosis insidiosi in horses were evaluated in 71 Costa Rican horses between 1982 to 1988. One vaccine used a cell-mass (CMV) as antigen and the other a soluble concentrated antigen (SCAV). Both vaccines cured horses infected with Pythium insidiosum (p value approximately 14%). The age of lesions prior to vaccination was important in the response of the horses to immunotherapy. All horses with lesions 0.5 months or less in duration were cured regardless of the vaccine used. Horses with lesions two or more months old did not respond to either vaccine. The age of the horses did not have any influence on their response to the vaccinations. The CMV produced a prominent inflammatory reaction at the side of injection, while the SCAV gave a low inflammatory reaction. In addition, the CMV lost its effectiveness two to three weeks after its preparation. By contrast, the SCAV maintained its ability to cure horses even after 18 months. Immunotherapy using SCAV can thus be used as the vaccine of choice in early cases of equine cutaneous pythiosis insidiosi.

Immunodiffusion test for diagnosis and monitoring of human pythiosis insidiosi

To facilitate the laboratory diagnosis of human cases of pythiosis insidiosi, an immunological test was evaluated. A soluble antigen was prepared from a human isolate of Pythium insidiosum, an aquatic, thermotolerant oomycete that causes infections in cattle, dogs, horses, and humans. Sera from seven proven cases of disseminated human pythiosis insidiosi were tested in an immunodiffusion test along with appropriate control sera from patients with a variety of actinomycotic, bacterial, and mycotic diseases as well as sera from uninfected individuals. Titers ranged from 1:1 to 1:32 in the seven serum samples from the disseminated cases of pythiosis insidiosi of varying severity. The heterologous sera gave negative reactions. The rapidity and specificity of the immunodiffusion test makes it a useful diagnostic tool for the serodiagnosis of P. insidiosum infections.

Nasal and retrobulbar mass in a cat caused by 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.

Review of animal mycoses in Australia

This review covers the available literature on the mycoses of animals in Australia since the last review published in 1967. Of the cutaneous infections, dermatophytoses have been recorded in a wide range of animals: cattle, horses, goats, pigs, sheep, cats, dogs, mice, guinea-pigs, rabbits, a lion, kangaroos, a camel, koalas and wallabies. These infections were caused by several species and varieties of the genera, Microsporum and Trichophyton. Eight agents of ringworms have been recorded in the horse. Two subcutaneous mycoses, phaeohyphomycosis and sporotrichosis have been reported. Phaeohyphomycosis is becoming more common but sporotrichosis is rare having been recorded only once in a cat. The following systemic mycoses have been recorded: adiaspiromycosis, aspergillosis, candidiasis, cryptococcosis, dactylariosis, fusariomycosis, histoplasmosis, miscellaneous mycoses, mycotic abortion and related conditions, zygomycosis, pythiosis, protothecosis and green algal infections. Cryptococcosis has affected 11 different animal species. Mycotic abortion is a serious disease in Victoria. Pythiosis of horses has been extensively studied in northern Australia.

Induction of zoospore formation in Thai isolates of Pythium insidiosum

Three human isolates of Pythium insidiosum De Cock 1987, the aetiologic agent of pythiosis, were induced for zoosporogenesis. The isolates were grown on Sabouraud glucose agar for 2 days before being inoculated into boiled spikelets of Axonopus compressus (Gramineae) and then into induction medium (IM). Optimum zoospore formation was demonstrated under the light microscope after incubation for 24 h at 37 degrees C in IM.

Canine pythiosis--isolation and identification of Pythium insidiosum

Pythium insidiosum was isolated from the subcutaneous tissue of a 1-year-old tan crossbreed dog and from the intestinal tract of an 18-month-old Samoyed male. Gomori's methenamine silver stain was superior to hematoxylin and eosin in demonstrating the organism in tissue sections. The agent was identified as P. insidiosum by zoospore formation in an aqueous yeast extract solution containing grass blades. Exoantigens produced in culture were shown to be identical to known P. insidiosum antigens by microimmunodiffusion.

Antigenic relationship between Pythium insidiosum de Cock et al. 1987 and its synonym Pythium destruens Shipton 1987

Antigens and rabbit-antisera from holotypes of Pythium insidiosum and P. destruens were prepared to elucidate their antigenic relationship. The antigens and rabbit-antisera of P. insidiosum as well as P. destruens used as a reference system showed that both shared three precipitin bands in common. The antigen and rabbit-antisera of P. destruens and P. insidiosum used as a reference system against other strains isolated from humans and animals with pythiosis, also showed three precipitin bands in common. When we used sera taken from horses with proven pythiosis against antigens of P. insidiosum and P. destruens, six common bands were observed. We concluded that the etiologic agent of pythiosis is a single species P. insidiosum, and could be identified by serologic methods.