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Blastocystis hominisBlastocystis is a microscopic single-cell organism (protozoan) that lives in the digestive tract. Many protozoans normally live in the digestive tract and are harmless or even helpful, but some cause disease.Blastocystis is a parasite — a microscopic single-celled organism (protozoan). Many protozoans normally live in your gastrointestinal tract and are harmless or even helpful; others cause disease.It's not clear whether blastocystis causes disease. Most people who carry the organism have no signs or symptoms, but it's also found in people who have diarrhea and other digestive problems. Blastocystis often appears with other organisms, so it's not known whether it causes disease.Experts suspect that blastocystis gets into the digestive system when people eat contaminated food or are exposed to the stool of a contaminated person, such as when changing a diaper in a child care setting. Rates of the organism in stool increase where there's inadequate sanitation and poor personal hygiene. Risk factorsBlastocystis hominis is common, and anyone can have the organism in his or her stools.
You might be at higher risk if you travel or live where sanitation is inadequate or where the water might not be safe or if you handle contaminated animals, such as pigs and poultry. ComplicationsIf you have diarrhea associated with Blastocystis hominis, it's likely to be self-limiting. However, anytime you have diarrhea, you lose vital fluids, salts and minerals, which can lead to dehydration. Children are especially vulnerable to dehydration.
Blastomycosis, caused by the dimorphic fungus Blastomyces (most commonly the species (spp.) B. Dermatitidis and B. Gilchristii), can cause a spectrum of disease ranging from subclinical to influenza-like illness to disseminated infection.It is acquired by inhaling airborne spores from the environment, particularly in areas with moist soil and decomposing organic material near fresh. The symptoms of blastomycosis are often similar to the symptoms of flu or other lung infections. Approximately half of people who are infected with the fungus Blastomyces will show symptoms. Department of Health & Human Services.
PreventionYou might be able to prevent Blastocystis hominis or other gastrointestinal infection by taking precautions, especially while traveling in high-risk countries. Watch what you eatThe general rule of thumb is this: If you can't boil it, cook it or peel it — forget it. Avoid food from street vendors. Don't eat soft-cooked eggs. Avoid unpasteurized milk and dairy products, including ice cream. Avoid raw or undercooked meat, fish and shellfish.
Steer clear of moist food at room temperature, such as sauces and buffet offerings. Eat foods that are well-cooked and served hot.
Stick to fruits and vegetables that you can peel yourself, such as bananas, oranges and avocados. Stay away from salads and fruits you can't easily peel, such as grapes and berries. Avoid frozen pops and flavored ice.
Skip salsa and other condiments made with fresh ingredients.Don't drink the waterWhen visiting high-risk countries, keep the following tips in mind:. Avoid unsterilized water — from tap, well or stream. If you need to drink or wash fruits or vegetables in local water, boil it for at least three minutes and let it cool to room temperature. Avoid ice cubes or fruit juices made with tap water.
Keep your mouth closed while showering. Use bottled water to brush your teeth. Make sure hot beverages, such as coffee or tea, are steaming hot.Feel free to drink canned or bottled drinks in their original containers — including water, carbonated beverages, beer or wine — as long as you break the seals on the containers yourself. Wipe off any can or bottle before drinking or pouring.You can chemically disinfect water with iodine or chlorine. Iodine tends to be more effective, but limit its use, because too much iodine can be harmful to your body.
Take precautions against passing a parasite to othersIf you have Blastocystis hominis or another gastrointestinal infection, good personal hygiene can help keep you from spreading the infection to others:.Wash hands with soap and water frequently, especially after using the toilet and before, during and after handling food. Rub soapy, wet hands together for at least 20 seconds before rinsing. Lather the backs of your hands and between your fingers.
Dry your hands well with a clean towel.If soap and water aren't available, use an alcohol-based hand sanitizer that contains at least 60 percent alcohol. Wash hands well after changing a diaper, especially if you work in a child care center, even if you wear gloves. Jameson JL, et al., eds. Protozoal infections. In: Harrison's Principles of Internal Medicine.
New York, N.Y.: The McGraw-Hill Companies; 2018. Accessed Dec. 8, 2018. Blastocystis spp.
Centers for Disease Control and Prevention. Accessed Dec. 8, 2018.
Leder K, et al. Blastocystis species. Accessed Dec. 8, 2018. Parasites — Nonpathogenic (harmless) intestinal protozoa.
Centers for Disease Control and Prevention. Accessed Dec. 8, 2018. Food and water safety. Centers for Disease Control and Prevention. Accessed Dec. 8, 2018.
Avoid foodborne illness when traveling abroad. Department of Health and Human Services. Accessed Dec. 8, 2018. When & how to wash your hands. Centers for Disease Control and Prevention.
Accessed Dec. 8, 2018. Freedman S. Oral rehydration therapy.
Accessed Dec.
doi: 10.1155/1996/657941
PMID: 22514432
Language: English | French
This article has been cited by other articles in PMC.
Abstract
In fall 1993 a man and a dog developed blastomycosis after visiting an island off Bayfield Inlet, Georgian Bay, located near Parry Sound, Ontario. The man recovered but the dog died of blastomycosis. It was hypothesized that the common source of exposure was the island since the permanent residences of the two cases were in different cities. One further case of human infection, based on positive serology, and four additional cases of probable canine blastomycosis were identified. All cases had travelled to Bayfield Inlet during summer and early fall 1993. To the authors’ knowledge this is the first Canadian report of a common source of infection of human and canine blastomycosis. This report also provides evidence for a new endemic area of blastomycosis infection.
RÉSUMÉ :
À l’automne de 1993, un homme et un chien ont développé une blastomycose après avoir visité une île au large de l’anse Bayfield dans la baie Georgienne, située près de Parry Sound, en Ontario. L’homme a récupéré, mais le chien est décédé de blastomycose. Selon une hypothèse, la source commune de l’exposition a été l’île, puisque les résidences permanentes de deux cas étaient situées dans des villes différentes. Un autre cas d’infection chez l’humain sur la base d’une sérologie positive et quatre autres cas de blastomycose canine probable ont été identifiés. Tous les cas s’étaient rendus à l’Anse Bayfield durant l’été et le début de l’automne 1993. Selon l’auteur, il s’agit du premier rapport canadien faisant état d’une source commune de blastomycose chez l’homme et le chien. Ce rapport confirme également l’existence d’une nouvelle région endémique de blastomycose.
North American blastomycosis is a fungal infection caused by Blastomyces dermatitidis. It is often a systemic illness involving lung, skin and bone. In North America blastomycosis is endemic in areas adjoining some of the major rivers and the Great Lakes. Important epidemiological information has been derived from outbreaks of blastomycosis, which have often involved recreational activities in wooded areas along waterways. Furthermore, ever since the illness was first described, it was known that dogs were susceptible to the infection. We describe a small outbreak of blastomycosis that involved dogs and humans who had visited an island in Georgian Bay, Ontario.
CASE PRESENTATION
Index case one:
A 44-year-old Caucasian male presented in October 1993 with an asymptomatic right upper lobe nodule detected by routine chest radiograph (Figure 1). There was a past medical history of malignant melanoma of the back diagnosed in 1979 with recurrence to the right groin in 1984. Both were treated with wide surgical resection. The patient had been disease-free since 1984. A chest radiograph in October 1992 was unremarkable. The patient was a physically fit non-smoker with no significant family or occupational history.
Human blastomycotic nodule. Chest x-ray of index case 1 showing a right upper lobe nodule
The patient lived in Toronto and travelled each summer to a small privately owned island off Bayfield Inlet in Georgian Bay, Ontario, located near Parry Sound and approximately 275 km north of Toronto. The island was inhabited by numerous animals including a brown bear, raccoons and beavers. The terrain included a marshy pond and several man-made dwellings. There had been no recent excavations.
Further investigations of the pulmonary nodule included routine blood work, bronchoscopy, computed tomography of the chest, abdominal ultrasound and fine needle biopsy. These investigations did not reveal evidence of metastatic melanoma or primary lung carcinoma.
The patient underwent open lung biopsy in November 1993. A well-defined lesion measuring 1×1.5 cm and a right bronchial lymph node were excised from the right upper lobe. There was no mediastinal lymphadenopathy. The nodule and lymph node revealed a nonnecrotizing granulomatous reaction with budding yeast cells characteristic of Blastomyces dermatitidis (Figure 2).
Index case 1, showing Blastomycoses dermatitidis stained with GMS. Pulmonary nodule ×432
The patient’s postoperative course was uncomplicated. Treatment with itraconazole 200 mg/day was initiated because of possible residual lymph node involvement. The patient completed three months of itraconazole therapy without complications. There was no clinical evidence of blastomycosis.
Index case two:
A previously well three-year-old male Dalmatian dog presented in October 1993 with worsening dyspnea. He was found to have severe pneumonia (Figure 3), generalized lymphadenopathy and several skin lesions. Aspiration of a lymph node and subcutaneous nodule revealed broad-based budding yeast consistent with B dermatitidis (Figure 4). Despite treatment with antifungal therapy the dog succumbed to the infection.
Canine blastomycosis. Chest x-ray of index case 2 showing diffuse pulmonary infiltrates
Index case 2, showing Blastomycoses dermatitidis stained with Fungi Fluor. Subcutaneous nodule ×432
The dog lived in the town of Oakville, 300 km from the island in question. The dog’s travel history was also positive for annual summer trips to the island visited by index case 1. The two cases shared no other common geographical exposure. Close contact between the two cases was minimal and neither had been injured by the other.
The common-source exposure of the two index cases is hypothesized to be the island described. In an attempt to identify other possible cases, an assessment was conducted of several individuals who visited the island during summer 1993. Eight additional subjects underwent clinical evaluation and serological testing (complement fixation and enzyme immunoassay) to determine the presence of infection with B dermatitidis. Informed consent was obtained from all human subjects or their parents or guardians who participated in this study. Guidelines for human experimentation were followed in the conduct of this clinical research. All results were negative, except for a positive enzyme immunoassay in the 11-year-old son of index case 1. He was asymptomatic.
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An informal survey of veterinarians from the adjacent Parry Sound region revealed four further cases of suspected canine blastomycosis. All four dogs had travelled to Bayfield Inlet during summer and early fall 1993. They presented with pneumonia and all four dogs died from the disease. In two of the four cases microscopic examination for B dermatitidis was undertaken and confirmed the diagnosis. Retrospective diagnoses of the other two cases were based on clinical findings only.
DISCUSSION
North American blastomycosis is caused by the dimorphic fungus B dermatitidis. The primary route of infection is by inhalation of the mycelial form. The fungus converts to the yeast form at body temperature (). Self-limiting pulmonary infection with complete resolution appears to be the most common clinical manifestation; however, more extensive pulmonary involvement including pleural disease and adult respiratory distress syndrome as well as extrapulmonary dissemination to the skin, bones, prostate, meninges, adrenal glands, lymph nodes and spleen can occur (–).
There have been nine published outbreaks of blastomycosis (Table 1) (–). A common source exposure was suggested in six, two of which involved both humans and dogs (,). Most outbreaks occurred in the summer and fall and were closely associated with contact with surface water. The most common presentation of culture-proven blastomycosis was asymptomatic pulmonary infection (57% of cases); disease was usually self-limited. Only one of the 130 human cases of blastomycosis reported in these nine outbreaks died (), whereas all nine dogs died (,). There was no evidence of canine-human transmission of infection. The incubation period, when estimated, ranged from 21 to 106 days (,). B dermatitidis was successfully isolated from the environment in only two of the outbreaks (,).
TABLE 1
Summary of nine outbreaks of blastomycosis: 1953–88
Month/year | N | M/F | Location | Diagnosis | Presentation | Rx | Cured/total | Source | Ref |
---|---|---|---|---|---|---|---|---|---|
10/53-05/54 | 11 | 6/5 | Grifton, NC | C 11, CF 3/8 | Pulm (S) 11/11 | 8/11 | 10/11 | ? | 4 |
11/72 | 12 | 7/5 | Bigfork, MN | C 4, CF 4 | Pulm (S) 7 | No | 12/12 | Wood cabin | 5 |
12/75-01/76 | 5 | 1/4 | Enfield, NC | C 5 | Pulm (S) 5 | ? | 5/5 | ? | 6 |
08/74-04/75 | 5 | 3/2 | Westmont, IL | C 5, CF 2 | Pulm (S) 4 Cut 1 | 5 | 5/5 | ? | 7 |
07/79 | 7 | 5/2 | Hayward, WI | C 5, CF & ID 0 | Pulm (S) 5 | No | 7/7 | Campsite canoeing | 8 |
Pulm (AS) 2 | |||||||||
03/84 | 4 | 0/4 | Southampton, VA | C 3, CF 2, ID 3, EIA 4 | Pulm (S) 4 | 4 | 4/4 | Hunting 4/4 dogs died | 9 |
06/84 | 48 | 16/32 | Wisconsin | C 9, CF 4, ID 13, EIA 37 | Pulm (S) 20 | 9 | 48/48 | Beaver lodge Bd isolated | 10 |
Pulm (AS) 11 | |||||||||
05-06/85 | 14 | 10/4 | Tomorrow & Crystal River, WI | C 11/14 EIA 9/14 | Pulm (S) 13 | 13 | 14/14 | Fishing timber fort Bd isolated | 11 |
Pulm (AS) 1 | |||||||||
06-11/88 | 22 | 10/12 | Watersmeet Lake, WI | C 3, CF & ID 0, EIA 18 | Pulm (S) 3, Cut 1, ASx 16 | 3 | 22/22 | Excavation of hotel 5/5 dogs died | 12 |
ASx Asymptomatic; Bd Blastomyces dermatitidis; C Positive culture; CF Positive complement fixation; Cut Cutaneous disease; EIA Positive enzyme immunoassay; ID Positive immunodiffusion; M/F Male/female; N Number of cases; Pulm (AS) Asymptomatic with abnormal chest x-ray; Pulm (S) Symptomatic pulmonary disease with abnormal chest x-ray; Rx Antifungal treatment
The endemic areas for B dermatitidis, based on the reported cases, occur in central, north-central and eastern United States with a propensity for the Ohio and Mississippi river basins and shores of Lake Michigan (). In Canada, the vast majority of cases occur in Quebec, Ontario and Manitoba (). In Ontario, the northeastern region of Lake Superior has been identified as an endemic area (). ‘North American blastomycosis’ is a misnomer for there have been reported cases in other areas of the world, such as Africa ().
Although blastomycosis is a relatively rare fungal disease in humans, in enzootic areas the incidence of canine disease is at least 10-fold higher. Compared with humans, dogs infected with B dermatitidis usually have a shorter incubation period, more extensive extrapulmonary dissemination and earlier progression of disease and death. Unlike that in humans, recovery from symptomatic infection in dogs is rare without treatment, most likely because of disseminated disease. Antifungal therapy in dogs is the same as in humans, with itraconazole being more effective than ketoconazole and equivalent in efficacy to amphotericin B. Fluconazole appears to be the least effective systemic antifungal (). With early effective antifungal therapy, cure rates in dogs reach 80%. The extent of pulmonary involvement has been shown to correlate with the likelihood of relapse and death (17).
The index cases described in this report likely represent a common source infection of human and canine blastomycosis. The source of exposure is believed to be the island in Georgian Bay. Evidence to support this hypothesis include the following: there was no other common source of exposure and the cases resided in separate permanent residences in different cities; there were documented additional cases of suspected canine blastomycosis from the same area during the same period; the incubation period was appropriate for blastomycosis; and there was no evidence of direct transmission. Although an attempt to culture B dermatitidis from the human index case was not successful, microscopic evaluation revealed strong evidence for B dermatitidis in both index cases. There was no attempt to culture B dermatitidis from the canine cases. Soil cultures from several parts of the island were negative for B dermatitidis. Serological testing of several human contacts who visited the island revealed one additional case of asymptomatic infection.
To our knowledge this is the first Canadian report of a common source infection of human and canine blastomycosis. The source of exposure, an island off Bayfield Inlet, Georgian Bay near Parry Sound, may represent a newly recognized endemic area of human blastomycosis infection in Ontario.
The clinician should be aware of endemic areas of blastomycosis when considering the differential diagnosis of pulmonary disease, especially in previously healthy individuals who are not responding to therapy. A detailed travel history and communication with a veterinarian from the area may provide important clinical clues to the diagnosis.
Acknowledgments
The authors thank Dr I Campbell for preparation of the histological slides, Dr N Gofton, Dr A Norris and Dr ACG Abrams-Ogg for their veterinary contribution and Ms Shirley Magnaye for her secretarial assistance.
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