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

Computed Tomography Finding of Crusty Thrombosed Arteries: An Appearance of Lower Extremity Vascular Pythiosis

Vascular pythiosis is a dreadful vascular infection that presents as a chronic leg ulcer. To distinguish this infectious disease from atherosclerotic occlusion of the lower limb, we investigated the imaging appearance and presence of thick and irregular arterial wall enhancement, named crusty thrombosed arterial sign, on computed tomography images in cases with vascular pythiosis infection of lower extremities. In this study, 13 cases of vascular pythiosis of lower extremities with available images from 2016 to 2022 were reviewed and the presence of crusty thrombosed arterial signs, segments of vascular involvement, and radiological findings of hematologic disease, including hepatosplenomegaly and bone changes were recorded. Crusty arterial sign with long segmental arterial involvement was found in all cases. All cases had hepatomegaly and abnormal spleen, either splenomegaly or splenectomy, found in 12 cases (92.3%). Six cases (46.1%) had thalassemic bone changes. We proposed the pathognomonic radiologic sign of vascular pythiosis: the crusty thrombosed arterial sign, which manifested as diffusely thick and irregular arterial wall enhancement along long arterial thrombosis without skip lesions. Other associated findings included splenomegaly, splenectomy, and thalassemic bone changes. These radiologic findings facilitated the diagnosis of vascular pythiosis, particularly in cases of atypical presentation or unreliable clinical context.

Retrospective Review of Management and Overall Survival Rate of Patients With Vascular Pythiosis of the Lower Extremity: 20 Years Experience

Pythiosis is an infectious disease in humans and animals caused by an aquatic fungus-like micro-organism, Pythium insidiosum. Vascular pythiosis is a difficult condition to treat and can lead to loss of limb in addition to being a potentially life-threatening infection. The condition is furthermore unfamiliar among healthcare workers, which often results in delayed treatment or even misdiagnosis. In this study, we report our findings, which have been gathered over a 20-year period in caring for vascular pythiosis in Maharaj Nakorn Chiang Mai Hospital, Chiang Mai, Thailand. We made a retrospective medical review of 32 patients presented with arterial occlusion who have serum anti-Pythium insidiosum antibodies. All patients underwent computed tomography angiography to confirm the level of arterial occlusion and decided on a treatment plan. Twelve out of 22 patients with infrainguinal disease, femoropopliteal or below-knee vascular occlusion, survived. The mean survival time is 6.58 years. Eight in 10 patients presented with suprainguinal disease died during the follow-up with a mean survival time of 31.6 months. The suprainguinal extension of the disease influenced the outcome, resulting in a higher mortality rate. However, patients presented with chronic limb ischemia had a much greater rate of survival compared to other clinical presentations. Extensive surgical resection combined with antifungal treatment and immunotherapy have proven to be effective in patients with vascular pythiosis in our findings.

Selection of an Appropriate In Vitro Susceptibility Test for Assessing Anti-Pythium insidiosum Activity of Potassium Iodide, Triamcinolone Acetonide, Dimethyl Sulfoxide, and Ethanol

The orphan but highly virulent pathogen Pythium insidiosum causes pythiosis in humans and animals. Surgery is a primary treatment aiming to cure but trading off losing affected organs. Antimicrobial drugs show limited efficacy in treating pythiosis. Alternative drugs effective against the pathogen are needed. In-house drug susceptibility tests (i.e., broth dilution, disc diffusion, and radial growth assays) have been established, some of which adapted the standard protocols (i.e., CLSI M38-A2 and CLSI M51) designed for fungi. Hyphal plug, hyphal suspension, and zoospore are inocula commonly used in the drug susceptibility assessment for P. insidiosum. A side-by-side comparison demonstrated that each method had advantages and limitations. Minimum inhibitory and cidal concentrations of a drug varied depending on the selected method. Material availability, user experience, and organism and drug quantities determined which susceptibility assay should be used. We employed the hyphal plug and a combination of broth dilution and radial growth methods to screen and validate the anti-P. insidiosum activities of several previously reported chemicals, including potassium iodide, triamcinolone acetonide, dimethyl sulfoxide, and ethanol, in which data on their anti-P. insidiosum efficacy are limited. We tested each chemical against 29 genetically diverse isolates of P. insidiosum. These chemicals possessed direct antimicrobial effects on the growth of the pathogen in a dose- and time-dependent manner, suggesting their potential application in pythiosis treatment. Future attempts should focus on standardizing these drug susceptibility methods, such as determining susceptibility/resistant breakpoints, so healthcare workers can confidently interpret a result and select an effective drug against P. insidiosum.

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.

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.

Pythium insidiosum and Acanthamoeba keratitis in a contact lens user

The oomycete Pythium and the protozoan Acanthamoeba can cause fulminant and recalcitrant keratitis, respectively. These infections are not only sight-threatening but can also threaten the structural integrity of the eye. A high index of suspicion is required to identify Pythium keratitis given its uncommon occurrence. Acanthamoeba keratitis is most commonly associated with contact lens wear. However, its coexistence with Pythium has not been reported. We present the successful management of a case of contact lens-related keratitis, coinfected with Pythium and Acanthamoeba.

Clinicopathological features and outcomes of pythiosis

OBJECTIVES

Vascular pythiosis is a life-threatening infection caused by the oomycete Pythium insidiosum. This article reports the clinical presentation, serodiagnosis, pathology, and outcomes seen at the authors' institution.

METHODS

The cases of patients with proven vascular pythiosis at Ramathibodi Hospital, Mahidol University, Bangkok, Thailand from January 2006 to December 2016 were analyzed retrospectively.

RESULTS

Thirteen patients were analyzed, eight of whom had underlying thalassemias. Of the remaining five patients, one had aplastic anemia, one had myelodysplasia, one had acute leukemia, one had cirrhosis, and one had alcoholism. Neutropenic patients showed a rapid clinical deterioration. Atypical presentations including carotid arteritis, aneurysm, brain abscess, and stroke occurred in the non-thalassemic patients. Serology yielded positive results in all cases, with a rapid turnaround time. Serology has the advantage of providing a presurgical diagnosis, which allows prompt surgery and clinical cure to be achieved. Pathology revealed a neutrophilic response in the acute phase and a later shift to granuloma. Immunotherapy in combination with itraconazole and terbinafine was given. The amputation rate was 77%, and disease-free surgical margins were achieved in five cases (38%). The mortality rate was 31%.

CONCLUSIONS

This study highlights new aspects of pythiosis, such as the unusual host, clinical presentation, serology as a marker for rapid diagnosis, histopathology, and outcomes. Early recognition of the disease with prompt multimodality treatment may improve survival.

Outcomes and factors influencing prognosis in patients with vascular pythiosis

OBJECTIVE

Vascular pythiosis, caused by Pythium insidiosum, is associated with a high mortality rate. We reviewed the outcomes and established the factors predicting prognosis of patients treated in our institution with surgery, antifungal therapy, or immunotherapy.

METHODS

We undertook a retrospective record review of patients with vascular pythiosis treated in Siriraj Hospital, Bangkok, Thailand, between January 2005 and January 2015. Patient characteristics, type of surgery, adjunctive antifungal treatment, adjunctive immunotherapy, and disease status of surgical arterial and surrounding soft tissue margins were recorded. We calculated the mortality rate and established factors predicting prognosis.

RESULTS

The records of 11 patients were reviewed. All patients had thalassemia. Nine patients (81.8%) had a history of contact with contaminated water. The clinical presentations were chronic ulcers (45.5%), toe gangrene (27.3%), pulsatile mass (27.3%), and acute limb ischemia (27.3%). Above-knee amputation was required in 10 patients (90.9%). The mortality rate was 36.4%. Independent variables between survivors and nonsurvivors were lack of an arterial disease-free surgical margin (P = .003), lack of a surrounding soft tissue disease-free surgical margin (P < .05), a suprainguinal lesion (P < .05) and duration of symptoms (P < .05). Adjuvant itraconazole, terbinafine, and Pythium vaccine have a role to play in patients with a disease-free arterial surgical margin but in whom infected surrounding soft tissue could not be completely excised.

CONCLUSIONS

Achieving adequate disease-free surgical margins-especially the arterial margin-at amputation or débridement is the most important prognostic factor in patients with vascular pythiosis. Early detection combined with a multidisciplinary approach to treatment, including surgery, antifungal agents, and immunotherapy, allows the best possible outcome to be obtained.

The elicitin-like glycoprotein, ELI025, is secreted by the pathogenic oomycete Pythium insidiosum and evades host antibody responses

Pythium insidiosum is a unique oomycete that can infect humans and animals. Patients with a P. insidiosum infection (pythiosis) have high rates of morbidity and mortality. The pathogen resists conventional antifungal drugs. Information on the biology and pathogenesis of P. insidiosum is limited. Many pathogens secrete proteins, known as effectors, which can affect the host response and promote the infection process. Elicitins are secretory proteins and are found only in the oomycetes, primarily in Phytophthora and Pythium species. In plant-pathogenic oomycetes, elicitins function as pathogen-associated molecular pattern molecules, sterol carriers, and plant defense stimulators. Recently, we reported a number of elicitin-encoding genes from the P. insidiosum transcriptome. The function of elicitins during human infections is unknown. One of the P. insidiosum elicitin-encoding genes, ELI025, is highly expressed and up-regulated at body temperature. This study aims to characterize the biochemical, immunological, and genetic properties of the elicitin protein, ELI025. A 12.4-kDa recombinant ELI025 protein (rELI025) was expressed in Escherichia coli. Rabbit anti-rELI025 antibodies reacted strongly with the native ELI025 in P. insidiosum’s culture medium. The detected ELI025 had two isoforms: glycosylated and non-glycosylated. ELI025 was not immunoreactive with sera from pythiosis patients. The region near the transcriptional start site of ELI025 contained conserved oomycete core promoter elements. In conclusion, ELI025 is a small, abundant, secreted glycoprotein that evades host antibody responses. ELI025 is a promising candidate for development of diagnostic and therapeutic targets for pythiosis.

Molecular detection of Pythium insidiosum from soil in Thai agricultural areas

Pythium insidiosum is an aquatic fungus-like organism in the kingdom Stramenopila that causes pythiosis in both humans and animals. Human pythiosis occurs in ocular, localized granulomatous subcutaneous and systemic or vascular forms. Individuals whose occupations involve exposure to aquatic habitats have an elevated risk of contracting pythiosis. Previously, we reported the first successful isolation of Pythium insidiosum from aquatic environmental samples by culture including confirmation using molecular methods. In this study, we show that P. insidiosum inhabitats moist soil environments in agricultural areas. A total of 303 soil samples were collected from 25 irrigation sources in the areas nearby the recorded home addresses of pythiosis patients residing in northern provinces of Thailand. P. insidiosum DNA was identified directly from each soil extract by using a nested PCR assay and subsequent phylogenetic analysis of the ribosomal intragenic spacer region. P. insidiosum DNA could be detected from 16 of the 25 soil sources (64%). Conventional culture methods were also performed, however all samples exhibited negative culture results. We conclude that both irrigation water and soil are the natural reservoirs of P. insidiosum. In endemic areas, the exposure to these environmental reservoirs should be considered a risk factor for hosts susceptible to pythiosis.

Outbreak of Pythium keratitis during rainy season: a case series

PURPOSE

To describe typical clinical and laboratory characteristics of severe fungal keratitis caused by Pythium insidiosum during the rainy season in Northeast Thailand and to report the efficacy of P. insidiosum vaccine in the treatment of Pythium keratitis.

METHODS

A series of hospital-based consecutive cases of Pythium keratitis were diagnosed and treated at Srinagarind Hospital (Khon Kaen University, Khon Kaen, Thailand). The clinical presentations, diagnostic tests, and management are described.

RESULTS

Severe fungal keratitis caused by P. insidiosum was diagnosed in 5 eyes of 4 patients between May 2009 and July 2009. All cases had a history of fungal keratitis after being exposed to contaminated water. Upon slit-lamp examination, subepithelial and superficial stromal opacities were observed in a reticular pattern in all cases. Pythium insidiosum was identified and confirmed by both microbiological culture and polymerase chain reaction. Clinical worsening was detected after conventional treatment with antifungal agents. Therapeutic penetrating keratoplasty with either donor cornea or scleral graft was performed together with topical antifungal administration and P. insidiosum vaccination. Subsequent evisceration was performed in 1 eye.

CONCLUSIONS

An outbreak of Pythium keratitis in Northeast Thailand was reported. Distinctive clinical features are a suggestive clue for early diagnosis. Combination treatment including topical antifungal agents, radical surgery, and P. insidiosum vaccine may be considered for the management of Pythium keratitis.

Diagnosis and treatment of truncal cutaneous pythiosis in a dog

CASE DESCRIPTION

A 4-year-old spayed female Boxer was evaluated for a cutaneous mass located on the dorsum. The mass had been present for 6 weeks and was increasing in size.

CLINICAL FINDINGS

A mass of approximately 10 cm in diameter was detected on the dorsum cranial to the right ilial wing. Histologic examination of a tissue sample from the mass led to the diagnosis of cutaneous pythiosis. Computed tomography of the abdomen and the mass were performed and revealed a contrast-enhancing soft tissue mass of the dorsum and enlarged intra-abdominal lymph nodes.

TREATMENT AND OUTCOME

The dog underwent surgical excision of the cutaneous mass, including 5-cm skin margins and deep margins of 2 fascial planes. The mass was completely excised on the basis of results of histologic examination of surgical margins. The dog received itraconazole and terbinafine by mouth for 3 months following surgery. Recheck examination at 20 months postoperatively showed no signs of recurrence of pythiosis at the surgical site.

CLINICAL RELEVANCE

Aggressive surgical excision in combination with medical treatment resulted in a favorable long-term (> 1 year) outcome in this dog. Thorough workup including diagnostic imaging and lymph node evaluation is recommended. If surgery is to be performed, skin margins of 5 cm and deep margins of 2 fascial planes are recommended.

Pythium insidiosum keratitis in contact lens wear: a case report

PURPOSE

The purpose of this study was to report a case of contact lens-related Pythium insidiosum corneal ulcer.

METHODS

The authors conducted an interventional case report. We report the clinical presentations, histopathologic findings, and treatments of a patient with P. insidiosum keratitis associated with contact lens wear.

RESULTS

A 22-year-old Thai woman presented to our clinic with a nonresponsive, progressive corneal ulcer of the left eye. Slit lamp examination showed a large central ulcer measuring 5.4 x 5.2 mm with underlying dense stromal infiltrates surrounded by subepithelial and superficial stromal opacity in a reticular pattern along with radial perineural-like infiltrates. Histopathologic examination revealed broad, branched, thin-walled nonparallel hyaline hyphae with rare septates consistent with P. insidiosum. The corneal culture confirmed the diagnosis. The infection recurred after multiple therapeutic penetrating keratoplasties. Enucleation was eventually performed to eradicate the infection. No definite report of contact lens-related P. insidiosum keratitis existed in the literature.

CONCLUSION

Pythium keratitis may present with central ulcer and radial keratoneuritis similar to acanthamoeba keratitis. Contact lens wear can be a risk factor for this infection. Increasing awareness, early diagnosis, and intervention may improve the prognosis.

Development of an immunochromatographic test for rapid serodiagnosis of human pythiosis

Human pythiosis is an emerging and life-threatening infectious disease caused by the fungus-like organism Pythium insidiosum. High rates of morbidity and mortality for patients with pythiosis are exacerbated by the lack of early diagnosis and an effective treatment. Here, we developed and evaluated an immunochromatographic test (ICT) for the diagnosis of human pythiosis, in comparison to a standard serological test of immunodiffusion (ID). Culture filtrate antigen of P. insidiosum was used to detect human anti-P. insidiosum antibody. Sheep anti-human immunoglobulin G-colloidal gold conjugate was used to generate an ICT signal. Thirty-three sera from patients with vascular (n = 27), ocular (n = 4), and cutaneous (n = 2) pythiosis and 181 control sera from healthy blood donors (n = 100), as well as patients with a variety of infectious (n = 56) and noninfectious (n = 25) diseases, were included in the test evaluation. The turnaround time for generating a result by the ICT was less than 30 min, while that for ID was approximately 24 h. Based on the results for all sera of pythiosis patients and the control groups, the ICT showed 88% sensitivity and 100% specificity and ID showed 61% sensitivity and 100% specificity. By both tests, false-negative results for sera from all ocular pythiosis patients were obtained. In addition, the ID test yielded false-negative results for sera from eight patients with vascular pythiosis and one patient with cutaneous pythiosis. It was concluded that the ICT is a rapid, user-friendly, and reliable serological test for the early diagnosis of vascular and cutaneous pythiosis.

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.

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.

Clinical and epidemiological analyses of human pythiosis in Thailand

BACKGROUND

Pythiosis is an emerging and life-threatening infectious disease in humans and animals that is caused by the pathogenic oomycete Pythium insidiosum. Human pythiosis is found mostly in Thailand, although disease in animals has been increasingly reported worldwide. Clinical information on human pythiosis is limited, and health care professionals are unfamiliar with the disease, leading to underdiagnosis, delayed treatment, and poor prognosis.

METHODS

To retrospectively study the clinical and epidemiological features of human pythiosis, we analyzed clinical data from patients with pythiosis diagnosed during the period of January 1985 through June 2003 at 9 tertiary care hospitals throughout Thailand.

RESULTS

A total of 102 cases of human pythiosis were documented nationwide. A substantial proportion (40%) of cases occurred in the last 4 years of the 18-year study interval. Clinical presentations fell into 4 groups: cutaneous/subcutaneous cases (5% of cases), vascular cases (59%), ocular cases (33%), and disseminated cases (3%). Almost all patients with cutaneous/subcutaneous, vascular, and disseminated pythiosis (85%) had underlying thalassemia-hemoglobinopathy syndrome. Most ocular cases (84%) were associated with no underlying disease. A majority of the patients were male (71%), were aged 20-60 years (86%), and reported an agricultural occupation (75%). Regarding treatment outcomes, all patients with disseminated infection died; 78% of patients with vascular disease required limb amputation, and 40% of these patients died; and 79% of patients with ocular pythiosis required enucleation/evisceration.

CONCLUSIONS

Here, we report, to our knowledge, the largest case study of human pythiosis. The disease has high rates of morbidity and mortality. Early diagnosis and effective treatment are urgently needed to improve clinical outcomes. Because P. insidiosum is distributed worldwide and can infect healthy individuals, an awareness of human pythiosis should be promoted in Thailand and in other countries.

Identification of a novel 74-kiloDalton immunodominant antigen of Pythium insidiosum recognized by sera from human patients with pythiosis

The oomycetous, fungus-like, aquatic organism Pythium insidiosum is the etiologic agent of pythiosis, a life-threatening infectious disease of humans and animals that has been increasingly reported from tropical, subtropical, and temperate countries. Human pythiosis is endemic in Thailand, and most patients present with arteritis, leading to limb amputation and/or death, or cornea ulcer, leading to enucleation. Diagnosis of pythiosis is time-consuming and difficult. Radical surgery is the main treatment for pythiosis because conventional antifungal drugs are ineffective. The aims of this study were to evaluate the use of Western blotting for diagnosis of human pythiosis, to identify specific immunodominant antigens of P. insidiosum, and to increase understanding of humoral immune responses against the pathogen. We performed Western blot analysis on 16 P. insidiosum isolates using 12 pythiosis serum samples. These specimens were derived from human patients with pythiosis who had different forms of infection and lived in different geographic areas throughout Thailand. We have identified a 74-kDa immunodominant antigen in all P. insidiosum isolates tested. The 74-kDa antigen was also recognized by sera from all patients with pythiosis but not by control sera from healthy individuals, patients with thalassemia, and patients with various infectious diseases, indicating that Western blot analysis could facilitate diagnosis of pythiosis. Therefore, the 74-kDa antigen is a potential target for developing rapid serodiagnostic tests as well as a therapeutic vaccine for pythiosis. These advances could lead to early diagnosis and effective treatment, crucial factors for better prognosis for patients with pythiosis.

Infections and thalassaemia

Infections are major complications and constitute the second most common cause of mortality and a main cause of morbidity in patients with thalassaemia, a group of genetic disorders of haemoglobin synthesis characterised by a disturbance of globin chain production. Thalassaemias are among the most common genetic disorders in the world. Predisposing factors for infections in thalassaemic patients include severe anaemia, iron overload, splenectomy, and a range of immune abnormalities. Major causative organisms of bacterial infections in thalassaemic patients are Klebsiella spp in Asia and Yersinia enterocolitica in western countries. Transfusion-associated viral infections (especially hepatitis C) can lead to liver cirrhosis and hepatocellular carcinoma. A unique and challenging infection detected in Asian patients is pythiosis, caused by a fungus-like organism, the mortality rate of which is very high. Because the prognosis for thalassaemia has much improved, with many patients surviving to the fifth decade of life in developed countries, it is mandatory to reduce mortality by recognising and presumptively treating infections in these patients as quickly as possible.

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.

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.

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.