Funguses, also called fungi, are spore-producing organisms which obtain their nourishment by absorbing food from the hosts on which they grow. Many species of fungi exist in the environment, but only a very few cause infections. The primary source of most infections is soil. Some fungal infections can cause disease in otherwise healthy animals. The infection may be localized or systemic (infecting the entire body). Systemic fungal diseases cause significant health problems and mortality with blastomycosis, histoplasmosis, coccidioidomycosis, and cryptococcosis representing the four most common systemic fungal diseases in dogs and cats.
Blastomycosis is caused by Blastomyces dermatitidis fungus which exists in the environment in two forms: a mycelial form (present in the environment and is contagious) and yeast (found in the tissues and is not contagieous). The mycelial form of blastomycosis can easily infect both humans and animals. Young male dogs, especially hunting dogs, are at higher risk for blastomycosis because of the increased contact with the contaminated soil. Canine blastomycosis most commonly affects the lungs and has a tendency to spread to other organs.
Blastomycosis is one of the most common systemic fungal infections in dogs in North America. In North America, blastomycosis is most prevalent in the Ohio, Missouri, and Mississippi river valleys. Infection with B. dermatitidis most commonly occurs following inhalation of conidiospores aerosolized from rotting wood or contaminated soil. Blastomyces dermatitidis is a thermally dimorphic fungus. If the host cannot clear the conidia via cell-mediated immunity, the conidia may transform into yeast at body temperature, reproduce asexually, and cause pulmonary disease. In yeast form, the fungus can spread throughout the body via blood or lymph nodes. Preferred sites of infection include lungs, skin, and eyes. Bony involvement has also been described in 14% to 60% of canine and human patients. If the disease is untreated while in the lungs, it may become invasive and disseminate to other organs and possibly to the central nervous system where fatal meningitis may develop. The cost of treating an infection can be expensive, and no vaccine against this infection is commercially available. The mortality rate exceeds 90% for dogs that do not receive prompt antifungal treatment (9). Blastomycosis is most commonly seen in large dogs, where the cost of treatment can exceed $1,000. Vaccine prevention would offer a cost-effective alternative for those dogs at risk in areas of high endemicity, but no commercial vaccine is available.
Blastomycosis is a significant health issue in humans and other mammals. This fungal infection often presents as a non-specific febrile illness that mimics viral and bacterial pneumonia, causing cough, fever, hospitalization and sometimes death. Moreover, dissemination of the infection to bone, skin, central nervous system and other organs is often observed. In dogs, it is thought to predominantly affect young, male, large sporting breeds, chiefly because of their propensity for outdoor activity. Only Minnesota considers canine blastomycosis a reportable disease, therefore the number of cases occurring nationally is grossly underestimated. In Minnesota, canine cases occurred at 2.5 times that of humans from 1999–2009.
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The typical route of infection is inhalation of Blastomyces. From the respiratory tract, the developing yeast form spread throughout the body and affect multiple organ systems, most commonly the lymphatic, skeletal and central nervous systems, eyes and skin. Disseminated disease is associated with lethargy, loss of appetite, fever, chronic cough, difficulty breathing, eye problems, and central nervous signs. Diagnosis is often delayed because blastomycosis can mimic many other disease processes, including bacterial pneumonia and malignancy. The disease may be aggressive and requires adequate treatment. The treatment of choice is itraconazole combined with systemic corticosteroids in dogs with ocular blastomycosis. Dogs with cardiovascular disease may have a worse prognosis.
- Epidemiology, diagnosis, and treatment of blastomycosis in dogs and cats.Brömel C, Sykes JE. Department of Population Health and Reproduction, School of Veterinary Medicine, University of California, Davis.
- Blastomyces dermatitidis antigen detection in urine specimens from dogs with blastomycosis using a competitive binding inhibition ELISA.Shurley JF, Legendre AM, Scalarone GM. Department of Biological Sciences, Idaho State University.
- Clinical and molecular epidemiology of veterinary blastomycosis in Wisconsin. Jennifer L Anderson1, Brian L Sloss2 and Jennifer K Meece1
- Carpal intra-articular blastomycosis in a Labrador retriever
- Blastomyces dermatitidis Yeast Lysate Antigen Combinations: Antibody Detection in Dogs with Blastomycosis
- Safety, Tolerability, and Immunogenicity of a Recombinant, Genetically Engineered, Live-Attenuated Vaccine against Canine Blastomycosis