Canine and feline histoplasmosis: A review of a widespread fungus - Veterinary Medicine
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Canine and feline histoplasmosis: A review of a widespread fungus
Infection with this pathogenic fungus most commonly results from inhaling spores from contaminated soil. The infection should be treated promptly to avoid dissemination, which carries a poorer prognosis.


VETERINARY MEDICINE


CLINICAL SIGNS

The clinical signs seen in dogs and cats with histoplasmosis vary depending on which form of infection has taken root.

Pulmonary histoplasmosis

Acute pulmonary histoplasmosis in dogs and cats is thought to be uncommon. In dogs, this form is characterized by a rapid onset of dyspnea and cyanosis. Dogs with chronic pulmonary histoplasmosis are presented for evaluation of a mild, chronic cough and a history of weight loss and inappetance.7 Coughing may be due to partial airway obstruction secondary to hilar lymphadenopathy.17 Most affected cats have disseminated disease, and, even with evidence of pulmonary involvement, they seldom cough.10,11,18 Other clinical signs of respiratory tract involvement include dyspnea and tachypnea.11

Canine disseminated histoplasmosis

Acute disseminated histoplasmosis affects multiple organs, with a history of illness of only a few days' duration in experimental animals.19 Gastrointestinal involvement was reported in 28 of 36 (78%) dogs with chronic disseminated histoplasmosis.8,9 Large bowel diarrhea, characterized by hematochezia, mucus, and tenesmus, is common.11 With disease progression into the small intestine, diarrhea may become watery and voluminous, and protein-losing enteropathy may occur.8-11

In addition to gastrointestinal signs, common nonspecific clinical signs of chronic disseminated histoplasmosis in dogs include weight loss, inappetence, and fever of unknown origin that is nonresponsive to antibiotic therapy.7-11,20

Abnormal lung sounds, with or without accompanying cough or dyspnea, are noted in fewer than 50% of dogs with disseminated histoplasmosis.11 Infiltration of the organism into other organs, including the liver, spleen, and bone marrow, may result in hepatomegaly, splenomegaly, or pallor associated with anemia.8,9 Less commonly reported clinical findings of canine disseminated histoplasmosis include

  • Vomiting21-23
  • Peripheral lymphadenopathy10,11,24,25
  • Polyarthropathy or fungal osteomyelitis10,11,26,27
  • Ulcerated dermal nodules, sores on footpads, or draining abscesses10,21,28-32
  • Neurologic signs, including seizures and vertical nystagmus33
  • Oral lesions, including gingival nodules and lingual erosions21,31
  • Conjunctivitis, chorioretinitis, retinal detachment, or optic neuritis26,34
  • Icterus9
  • Pleural and peritoneal effusion7,23,35

Feline disseminated histoplasmosis

Clinical signs of feline disseminated histoplasmosis are often chronic and nonspecific. Weight loss, pale mucous membranes, lethargy, pyrexia, anorexia, and dehydration were the predominant findings in 12 cats with disseminated histoplasmosis. Five of the 12 cats were tachypneic with abnormal lung sounds.15 A review of 96 cases reported weakness, lethargy, emaciation, dehydration, and pyrexia as the most common signs.1 Respiratory signs such as dyspnea, tachypnea, and occasional coughing were noted in 39% of the cats.1

While sometimes reported to be uncommon, ocular involvement may occur in disseminated histoplasmosis more often than in other systemic mycoses in cats.1,36 In a review of 96 cats with histoplasmosis, 24% of the cats had ocular involvement including chorioretinitis, anterior uveitis, or retinal detachments.1 Granulomatous chorioretinitis occurs, possibly because of H. capsulatum in the choroid and retina.34,37 Additional ocular involvement may include retinal hemorrhage, optic neuritis, and fungal granulomas.15,38,39

About one-third of affected cats may have lymphadenopathy, splenomegaly, or hepatomegaly, occasionally accompanied by icterus.11 In contrast to dogs, primary intestinal histoplasmosis is unusual in cats; in one cat, this form of histoplasmosis caused vomiting and watery diarrhea with hematochezia.40

Cutaneous lesions, infrequently reported, are nodular or ulcerated and may exude serosanguineous fluid.11,32,38,41-44 Neurologic signs also occur.45 Rare clinical findings include nasal polyps and oral and lingual ulceration.10,11


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