Disseminated pythiosis in three horses

Nucleic Acid-Based Detection of Pythium insidiosum: A Systematic Review

Pythiosis, a life-threatening infectious condition caused by Pythium insidiosum, has been increasingly reported in humans and animals worldwide. Antifungal drugs usually fail to control the pathogen. The surgical removal of an infected organ is the treatment of choice. Many affected patients die due to advanced infection. A timely and accurate diagnosis could lead to a better prognosis in pythiosis patients and save their lives. Although a standard culture method is available in microbiological laboratories, it is time-consuming, laborious, and insensitive for P. insidiosum identification. Immunological assays have been developed to improve the diagnosis of pythiosis. However, immunological methods are commercially unavailable and primarily detect anti-P. insidiosum antibodies, which constitute indirect evidence of pythiosis, making it challenging to differentiate a past from a recent infection. Moreover, such immunological tests cannot diagnose patients with a local infection, such as in the eye. Nucleic acid-based tests (NATs) are efficient for the direct and rapid detection of P. insidiosum DNA in trace-amount or culture-negative specimens. The reagents and equipment required for NATs are usually available in molecular diagnostic laboratories. Herein, we provide a systematic review to comprehensively present the principal and clinical usages, advantages, and limitations of such NATs in the detection of P. insidiosum. Various NATs have been established to detect P. insidiosum, which can be classified into amplification-based (i.e., PCR assays, isothermal tests, and next-generation sequencing methods) and non-amplification-based (i.e., DNA hybridization) techniques. This concise review on NATs constitutes an up-to-date reference with which healthcare professionals can learn about and decide upon which detection method is suitable for their respective laboratory environments.

Nested PCR Detection of Pythium sp. from Formalin-Fixed, Paraffin-Embedded Canine Tissue Sections

Simple Summary

Pythium insidiosum is a waterborne fungus-like organism commonly present in tropical and subtropical areas that causes a disease named pythiosis in dogs and other animals. This disease can cause inflammatory lesions on the skin and gastrointestinal tract and, if left untreated, may be fatal. Because this mold lacks the distinctive features of true fungi, it requires specific treatment. Diagnosis of pythiosis is commonly achieved by microscope visualization after staining the tissue sections (histopathology). Although some stains highlight hyphae, these techniques are challenging to distinguish P. insidiosum from other fungi. Our study aimed to develop a molecular technique (nested PCR) to specifically detect P. insidiosum DNA in biopsy specimens to aid in diagnosing this organism. Archived biopsies from 26 dogs suspected of pythiosis were examined by histopathology with special stains and tested by the novel nested PCR. Agreement between histopathology and nested PCR occurred in 18/26 cases. The microscopic examination identified hyphae consistent with Pythium sp. in 57.7% of the samples, whereas the nested PCR detected P. insidiosum DNA in 76.9% of samples, aiding in the sensitivity of the diagnosis of pythiosis in dogs. Using this combination of techniques, we report 20 canine cases of pythiosis over 18 years in Indiana and Kentucky, an unexpectedly high incidence for temperate climatic regions. Thus, we recommend using our nested PCR test in addition to the microscopic examination to increase the sensitivity of the diagnosis.

Abstract

Pythium insidiosum is an infectious oomycete affecting dogs that develop the cutaneous or gastrointestinal form of pythiosis with a poor prognosis. If left untreated, pythiosis may be fatal. This organism is not a true fungus because its cell wall and cell membrane lack chitin and ergosterol, respectively, requiring specific treatment. Identifying the organism is challenging, as a hematoxylin and eosin (H&E) stain poorly stain the P. insidiosum hyphae and cannot be differentiated conclusively from other fungal or fungal-like organisms (such as Lagenidium sp.) morphologically. Our study aimed to develop a nested PCR to detect P. insidiosum and compare it with the traditional histopathologic detection of hyphae. Formalin-fixed, paraffin-embedded (FFPE) tissue scrolls from 26 dogs with lesions suggesting the P. insidiosum infection were assessed histologically, and DNA was extracted from the FFPE tissue sections for nested PCR. Agreement between the histologic stains, (H&E), periodic acid–Schiff (PAS), and/or Grocott methenamine silver (GMS) and the nested PCR occurred in 18/26 cases. Hyphae consistent with Pythium sp. were identified via histopathology in 57.7% of the samples, whereas the nested PCR detected P. insidiosum in 76.9% of samples, aiding in the sensitivity of the diagnosis of pythiosis in dogs. Using this combination of techniques, we report 20 canine cases of pythiosis over 18 years in Indiana and Kentucky, an unexpectedly high incidence for temperate climatic regions. Using a combination of histopathology evaluation and nested PCR is recommended to aid in the accurate diagnosis of pythiosis.

Global Distribution and Clinical Features of Pythiosis in Humans and Animals

Pythiosis is a difficult-to-treat infectious disease caused by Pythium insidiosum. The condition is unfamiliar among healthcare workers. Manifestation of pythiosis is similar to other fungal infections, leading to misdiagnosis and delayed treatment. The geographical extent of pythiosis at a global scale is unclear. This study aimed to analyze the clinical information recorded in the scientific literature to comprehensively project epidemiological characteristics, clinical features, and future trends of pythiosis. From 1980 to 2021, 4203 cases of pythiosis in humans (n = 771; 18.3%) and animals (primarily horse, dog, and cow; n = 3432; 81.7%), with an average of 103 cases/year, were recruited. Pythiosis case reports significantly increased in the last decade. Pythiosis spanned 23 tropical, subtropical, and temperate countries worldwide. Some patients acquired pythiosis from a trip to an endemic country. Strikingly, 94.3% of human cases were in India and Thailand, while 79.2% of affected animals were in the U.S.A. and Brazil. Clinical features of pythiosis varied. Vascular and ocular pythiosis were only observed in humans, whereas cutaneous/subcutaneous and gastrointestinal infections were predominant in animals. Mortality depended on host species and clinical forms: for example, none in patients with ocular pythiosis, 0.7% in cows with a cutaneous lesion, 26.8% in humans with vascular disease, 86.4% in dogs with gastrointestinal pathology, and 100% in several animals with disseminated infection. In summary, this study reports up-to-date epidemiological and clinical features of pythiosis in humans and animals. It increases awareness of this life-threatening disease, as the illness or outbreak can exist in any country, not limited to the endemic areas.

Pythiosis in Equidae in Northeastern Brazil: 1985-2020

The epidemiologic, clinical, pathologic, microbiological and immunohistochemical findings of pythiosis in equidae in northeastern Brazil are described. From January 1985 to December 2020 the Laboratory of Animal Pathology of the Federal University of Campina Grande received 1,331 tissue samples of equidae, 202 (15.17%) of which were diagnosed as pythiosis. Equidae of both sexes with ages varying from 4 months to 25 years were affected. Most animals were mixed breed (79.7%) and reared in an extensive system (73.26%). The disease occurred throughout the year but the highest incidence (70.29%) was noted after the rainy season. The clinical course was always chronic. The lesions were preferentially located on the limbs and ventral thoracoabdominal wall and characterized by nodules or tumor-like masses with ulcerations and serosanguineous discharge. The cut surface showed fistulous tracts containing kunkers. The direct examination of the kunkers and microbiological culture revealed sparsely septate and branched hyaline hyphae. Histopathology revealed a marked inflammatory infiltrate of eosinophils with multifocal well-defined areas of eosinophil necrosis and collagenolysis and intralesional negatively-stained hyphal profiles; in the donkey, a pyogranulomatous inflammatory infiltrate was noted surrounding these areas. Immunohistochemistry for Pythium insidiosum revealed strong immunolabelling of the hyphae. Pythiosis occurs endemically in equidae in northeastern Brazil, with seasonal variation in the incidence. The intralesional kunkers establishes an accurate presumptive diagnosis, but confirmation should preferably be performed through histopathology associated with immunohistochemistry, culture-based or molecular methods.

History and Perspective of Immunotherapy for Pythiosis

The fungus-like microorganism Pythium insidiosum causes pythiosis, a life-threatening infectious disease increasingly reported worldwide. Antimicrobial drugs are ineffective. Radical surgery is an essential treatment. Pythiosis can resume post-surgically. Immunotherapy using P. insidiosum antigens (PIA) has emerged as an alternative treatment. This review aims at providing up-to-date information of the immunotherapeutic PIA, with the focus on its history, preparation, clinical application, outcome, mechanism, and recent advances, in order to promote the proper use and future development of this treatment modality. P. insidiosum crude extract is the primary source of immunotherapeutic antigens. Based on 967 documented human and animal (mainly horses) pythiosis cases, PIA immunotherapy reduced disease morbidity and mortality. Concerning clinical outcomes, 19.4% of PIA-immunized human patients succumbed to vascular pythiosis instead of 41.0% in unimmunized cases. PIA immunotherapy may not provide an advantage in a local P. insidiosum infection of the eye. Both PIA-immunized and unimmunized horses with pythiosis showed a similar survival rate of ~70%; however, demands for surgical intervention were much lesser in the immunized cases (22.8% vs. 75.2%). The proposed PIA action involves switching the non-protective T-helper-2 to protective T-helper-1 mediated immunity. By exploring the available P. insidiosum genome data, synthetic peptides, recombinant proteins, and nucleic acids are potential sources of the immunotherapeutic antigens worth investigating. The PIA therapeutic property needs improvement for a better prognosis of pythiosis patients.

Prospecting Biomarkers for Diagnostic and Therapeutic Approaches in Pythiosis

Pythiosis, whose etiological agent is the oomycete Pythium insidiosum, is a life-threatening disease that occurs mainly in tropical and subtropical countries, affecting several animal species. It is frequently found in horses in Brazil and humans in Thailand. The disease is difficult to diagnose because the pathogen's hyphae are often misdiagnosed as mucoromycete fungi in histological sections. Additionally, there is no specific antigen to use for rapid diagnosis, the availability of which could improve the prognosis in different animal species. In this scenario, we investigated which P. insidiosum antigens are recognized by circulating antibodies in horses and humans with pythiosis from Brazil and Thailand, respectively, using 2D immunoblotting followed by mass spectrometry for the identification of antigens. We identified 23 protein spots, 14 recognized by pooled serum from horses and humans. Seven antigens were commonly recognized by both species, such as the heat-shock cognate 70 KDa protein, the heat-shock 70 KDa protein, glucan 1,3-beta-glucosidase, fructose-bisphosphate aldolase, serine/threonine-protein phosphatase, aconitate hydratase, and 14-3-3 protein epsilon. These results demonstrate that there are common antigens recognized by the immune responses of horses and humans, and these antigens may be studied as biomarkers for improving diagnosis and treatment.

Diseases caused by Pythium insidiosum in sheep and goats: a review

Pythiosis is characterized most commonly by ulcerative dermatitis, mainly in the limbs of sheep and occasionally of goats. In sheep, Pythium insidiosum is also responsible for necrotizing rhinitis characterized by marked enlargement and deformity of the nasal region, severe respiratory difficulty, and bloody nasal discharge. A third form of pythiosis in sheep affects the digestive tract, involving ulceration of the esophagus, forestomachs, and abomasum. Pythiosis in sheep and goats has been reported only in Brazil where it occurs mainly in the semiarid region of the country, when animals congregate and stay for longer periods of time within or around water reservoirs. However, it has been reported as well in areas of humid environments, such as the Pantanal of Mato Grosso and in the Brazilian Cerrado. The diagnosis of the different presentations of pythiosis is based on gross and microscopic findings, coupled with detection of the agent by immunohistochemical, molecular, and/or culture-based methods.

Review of methods and antimicrobial agents for susceptibility testing against Pythium insidiosum

Pythiosis is a life-threatening infectious disease of humans and animals caused by the oomycete microorganism Pythium insidiosum. The disease has been increasingly diagnosed worldwide. P. insidiosum inhabits freshwater and presents in two forms: mycelium and zoospore. Clinical manifestations of pythiosis include an infection of the artery, eye, skin, or gastrointestinal tract. The management of pythiosis is problematic due to the lack of effective treatment. Many patients die from an uncontrolled infection. The drug susceptibility testing provides clinically-useful information that could lead to proper drug selection against P. insidiosum. Currently, no standard CLSI protocol for the drug susceptibility of P. insidiosum is available. This review aims at describing methods and antimicrobial agents for susceptibility testing against P. insidiosum. Several in-house in vitro susceptibility methods (i.e., broth microdilution method, radial growth method, and agar diffusion method) have been established for P. insidiosum. Either mycelium or zoospore can be an inoculum. Rabbit is the commonly-used model of pythiosis for in vivo drug susceptibility testing. Based on the susceptibility results (i.e., minimal inhibitory concentration and inhibition zone), several antibacterial and antifungal drugs, alone or combination, exhibited an in vitro or in vivo effect against P. insidiosum. Some distinct compounds, antiseptic agents, essential oils, and plant extracts, also show anti-P. insidiosum activities. Successfully medical treatment, guided by the drug susceptibility data, has been reported in some pythiosis patients. Future studies should emphasize finding a novel and effective anti-P. insidiosum drug, standardizing in vitro susceptibility method and correlating drug susceptibility data and clinical outcome of pythiosis patients for a better interpretation of the susceptibility results.

Lung lesions of slaughtered horses in southern Brazil

ABSTRACT: Respiratory diseases cause significant veterinary costs, reduce performance and require withdrawal of horses. Yet, studies of the causes of pneumonia in horses are scant. This study aimed to describe the pathological and microbiological features of lung lesions in slaughtered horses in southern Brazil. In this study, 84 samples of lungs were examined, and a conclusive diagnosis was obtained in 74 cases. These were composed of bronchopneumonia in 50 cases, followed by granulomatous eosinophilic pneumonia (9/74), recurrent airway obstruction (7/74), lung fibrosis (4/74), lung hemorrhage (3/74) and pulmonary pythiosis (1/74). Bronchopneumonia had grossly firm focally extensive yellow to dark-red areas, which consisted microscopically of multifocal to coalescing infiltrate of degenerate neutrophils. Streptococcus equi subsp. zooepidemicus was identified in 21 of the 50 cases. Granulomatous eosinophilic pneumonia had multifocal pinpoint firm-hard yellow areas, which microscopically were composed of granulomas with a mineralized center surrounded by collagen fibers and severe infiltrate of eosinophils. Recurrent airway obstruction had mild multifocal pinpoint firm white areas that consisted microscopically of large amounts of mucus inside bronchi and bronchiole. Lung fibrosis had two patterns: focally extensive areas of consolidation and firm nodular areas. Microscopically, the first pattern had interstitial to peribronchial fibrosis, while the second had, in addition to the interstitial fibrosis, a severe pneumocyte hyperplasia and an alveolar infiltrate of neutrophils and macrophages with rare intranuclear inclusion bodies (equine herpesvirus 5, EHV-5). Pulmonary pythiosis presented a focal firm nodular area, with multiple kunkers observed in the cut surface, which corresponded microscopically to areas of necrosis surrounded by a mixed inflammatory infiltrate. At the periphery of the necrotic areas, multiple negatively stained hyphae were observed, which were evidenced through Grocott’s stain and immunohistochemistry anti-Pythium insidiosum.

PCR amplification of a putative gene for exo-1,3-β-glucanase to identify the pathogenic oomycete Pythium insidiosum

Background: Pythium insidiosum is the etiologic agent of pythiosis, a life-threatening infectious disease. Diagnosis of pythiosis is difficult and often delayed. Early diagnosis can lead to prompt treatment, and therefore a better prognosis for patients with pythiosis. Molecular diagnostic techniques are useful if microbiological and immunological assays are not available, or in cases of suspected pythiosis that test negative by other methods. So far, PCR identification of P. insidiosum has been largely relied on amplification of the rDNA region.

Objective: To evaluate the diagnostic performance of Dx3 and Dx4 primers specific for a putative gene for exo- 1,3-β-glucanase (PinsEXO1), which encodes a specific immunogen of P. insidiosum, for rapid single-round PCR identification of P. insidiosum, in comparison with the previously-reported rDNA-specific primers, ITSpy1 and ITSpy2.

Materials and Methods: Genomic DNA (gDNA) from 35 P. insidiosum isolates and 48 control organisms were prepared to evaluate the diagnostic performance of the PinsEXO1- and rDNA-specific primers.

Results: When amplifying the control gDNA by using the Dx3/4 and ITSpy1/2 primer sets, no PCR product was observed, indicating that both primer sets had 100% detection specificity. When amplifying the P. insidiosum gDNA, the Dx3/4 primers provided an expected 550-bp amplicon for all 35 isolates, while the ITSpy1/2 primers provided an expected 230-bp amplicon for only 32 isolates. Thus, detection sensitivity of the Dx3/4 and ITSpy1/2 primer sets were 100% and 91%, respectively.

Conclusion: By using the Dx3/4 primers, PinsEXO1 was an alternative, efficient, and novel PCR target for rapid single-round PCR identification of P. insidiosum.

Detection of the oomycete Pythium insidiosum by real-time PCR targeting the gene coding for exo-1,3-β-glucanase

Pythiosis is a life-threatening infectious disease caused by Pythium insidiosum. Early and accurate diagnosis is the key to prompt treatment and an improved prognosis for patients with pythiosis. An alternative to microbiological and immunological approaches for facilitating diagnosis of pythiosis is the PCR-based assay. Until recently, the ribosomal DNA (rDNA) region was the only target available for PCR-based detection of P. insidiosum. Failure to detect P. insidiosum by PCR amplification using the rDNA-specific primers has been reported. PinsEXO1, encoding an exo-1,3-β-glucanase, is an alternative, novel and efficient target for identification of P. insidiosum by conventional PCR. In this study, we aimed to develop a real-time (RT)-PCR approach targeting PinsEXO1 and compare its performance with conventional PCR for the detection of P. insidiosum. Both conventional and RT-PCR assays were positive for all 35 P. insidiosum strains tested, whilst all 58 control fungi were negative. The turnaround time for conventional PCR was 10 h, whilst that for RT-PCR was 7.5 h. The lowest amounts of genomic DNA template required for successful amplification by conventional and RT-PCR were 1 and 1 × 10(-4) ng, respectively. In conclusion, the RT-PCR assay retained 100% sensitivity and 100% specificity for detection of P. insidiosum. It showed a substantially improved analytical sensitivity and turnaround time that could improve diagnosis of pythiosis. The assay could also facilitate quantitative DNA analysis and epidemiological studies of P. insidiosum.

Update on pythiosis immunobiology and immunotherapy

Pythiosis is an invasive, ulcerative, pyogranulomatous disease caused by Pythium insidiosum, a fungus-like oomycete that has been reported to affect humans, horses, dogs, and other mammals mainly in tropical and subtropical areas of the world. The disease is characterized by an eosinophilic granulomatous and a Th2 immune response which in turn helps to protect the fungus from the host cells. Pythiosis can present clinically in subcutaneous, gastrointestinal, and vascular tissues or in a systemically disseminated form depending on the species and site of infection. Changes in iron metabolism and anemia are commonly observed. The diagnosis is accomplished through clinical and pathological features, laboratory characteristics of cultures, serological and molecular tests. Treatment includes radical surgery, antimicrobial drugs, immunotherapy or a combination of these treatments. Immunotherapy is a practical and non-invasive alternative for treating pythiosis which is believed to promote a switch from a Th2 to Th1 immune response, resulting in a favorable clinical response. This therapy has demonstrated cure rates above 70% and 55% in horses and humans but low cure rates in dogs and cats. Despite the curative properties of this type of immunotherapy, the antibodies that are produced do not prevent host reinfection. Thus, development of effective adjuvants and new diagnostic techniques for early disease diagnosis are of utmost importance. The aim of this review was to promote pythiosis awareness and to provide an update about the immunotherapy and immunobiology of this disease.

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.

Complications of equine wound management and dermatologic surgery

Complications of wounds and cosmetic surgery can be accurately managed with a combination of timely surgical and medical intervention to ensure the best possible outcome. The lack of soft tissue protection and a large quantity of susceptible synovial, tendon, ligament, and neurovascular structures make early and meticulous evaluation of limb wounds critical. Skin grafting is usually used following a period of open wound management and after healthy granulation tissue formation. Penetrating wounds of the abdomen or thorax have a guarded prognosis resulting from the ensuing potential for infection and pneumothorax. Gunshot wounds limited to the skeletal muscles have a good prognosis, whereas injuries that involve vital organs decreased survivability.

Cutaneous pythiosis in a nestling white-faced ibis

A nestling white-faced ibis (Plegadis chihi) with multifocal skin ulcerations on the wings, neck, head, and limbs was found in a wetland agricultural region of the central valley in California. Pathologic, microbiologic, and molecular findings were consistent with restricted, cutaneous infection by the oomycete Pythium insidiosum. The microscopic features of the disease, including intense, necrotizing eosinophilic and granulomatous inflammation, are similar to those previously described in mammals. Pythiosis, which is most typical in tropical and subtropical climates, has recently emerged in California as a cause of cutaneous and enteric disease in horses and dogs, respectively. Environmental stability and persistence of a "water-mold" in the arid central valley of California could be associated with agricultural and community watering practices. To the best of the authors' knowledge, this is the first published report of pythiosis in birds.

Pythium insidiosum: relato do primeiro caso de infecção humana no Brasil

A pitiose é causada por microorganismo aquático, fungo-símile, o Pythium insidiosum, patógeno de homens e animais. Observou-se um paciente com úlcera fagedênica no membro inferior, com exame anatomopatológico sugestivo de zigomicose, pouco sensível à terapêutica antifúngica, obtendo-se cura por meio de ampla exérese. A comprovação etiológica resultou de métodos moleculares, com amplificação e seqüenciamento de DNA de organismo isolado em ágar Sabouraud, observando-se 100% de analogia com seqüências de P. insidiosum depositadas no GenBank.

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.

Human pythiosis, Brazil

Pythiosis, caused by Pythium insidiosum, occurs in humans and animals and is acquired from aquatic environments that harbor the emerging pathogen. Diagnosis is difficult because clinical and histopathologic features are not pathognomonic. We report the first human case of pythiosis from Brazil, diagnosed by using culture and rDNA sequencing.

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.

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.