Histoplasmosis in horses

Genotypic diversity, virulence, and molecular genetic tools in Histoplasma

SUMMARYHistoplasmosis is arguably the most common fungal respiratory infection worldwide, with hundreds of thousands of new infections occurring annually in the United States alone. The infection can progress in the lung or disseminate to visceral organs and can be difficult to treat with antifungal drugs. Histoplasma, the causative agent of the disease, is a pathogenic fungus that causes life-threatening lung infections and is globally distributed. The fungus has the ability to germinate from conidia into either hyphal (mold) or yeast form, depending on the environmental temperature. This transition also regulates virulence. Histoplasma and histoplasmosis have been classified as being of emergent importance, and in 2022, the World Health Organization included Histoplasma as 1 of the 19 most concerning human fungal pathogens. In this review, we synthesize the current understanding of the ecological niche, evolutionary history, and virulence strategies of Histoplasma. We also describe general patterns of the symptomatology and epidemiology of histoplasmosis. We underscore areas where research is sorely needed and highlight research avenues that have been productive.

Reproductive Disorders in Horses

Reproductive disease is relatively common in the horse, resulting in a variable, yet significant, economic impact on individual horsemen as well as the entire industry. Diverse expertise from the veterinary community ensures and improves individual and population health of the horse. From a pathology and diagnostics perspective, this review provides a comprehensive overview of pathology of the male and female equine reproductive tract. Recognition by clinical and gross features is emphasized, although some essential histologic parameters are included, as appropriate. Where relevant, discussion of ancillary diagnostic tests and approaches are included for some diseases and lesions.

Update on fungal respiratory disease in horses

Fungal respiratory disease is a rare occurrence in horses. Fungal organisms are ubiquitous in the equine environment; however, there is a geographic predisposition for disease development, with fungal respiratory infections seen more commonly by practitioners working in tropical or subtropical environments. Diagnosis and treatment of fungal respiratory infections pose a challenge for the equine practitioner, and the prognosis for complete resolution of infection is often guarded; however, new antifungal medications are likely to improve treatment success. This article summarizes the available literature regarding the cause, diagnosis, and treatment of equine fungal respiratory disease.

Fungal diseases of horses

Among diseases of horses caused by fungi (=mycoses), dermatophytosis, cryptococcosis and aspergillosis are of particular concern, due their worldwide diffusion and, for some of them, zoonotic potential. Conversely, other mycoses such as subcutaneous (i.e., pythiosis and mycetoma) or deep mycoses (i.e., blastomycosis and coccidioidomycosis) are rare, and/or limited to restricted geographical areas. Generally, subcutaneous and deep mycoses are chronic and progressive diseases; clinical signs include extensive, painful lesions (not pathognomonic), which resemble to other microbial infections. In all cases, early diagnosis is crucial in order to achieve a favorable prognosis. Knowledge of the epidemiology, clinical signs, and diagnosis of fungal diseases is essential for the establishment of effective therapeutic strategies. This article reviews the clinical manifestations, diagnosis and therapeutic protocols of equine fungal infections as a support to early diagnosis and application of targeted therapeutic and control strategies.

Histologic and molecular identification of disseminated Histoplasma capsulatum in a captive brown bear (Ursus arctos)

A 33-year-old brown bear (Ursus arctos) was evaluated for chronic cough, partial anorexia, and lethargy in early fall of 2009. Radiographs revealed a generalized increase in interstitial density with focal lung field consolidation and air bronchograms more prevalent in the cranial lung lobes. Tracheal sputum and wash fluid grew mixed bacteria and 2 species of Candida on bacterial and fungal cultures, respectively. Serum was negative for antibodies to Aspergillus, Blastomyces, Coccidioides, and Histoplasma by semiquantitative radial immunodiffusion. Antimicrobial and antifungal treatment was administered. The bear died 1 month after entering hibernation. Gross necropsy revealed coalescent nodules and sheets of firm tan tissue covering pleural surfaces of the thoracic cavity and within pulmonary parenchyma, enlarged mesenteric lymph nodes, and intestinal ulcerations. Histopathology revealed granulomatous inflammation with intrahistiocytic yeast, consistent with Histoplasma organisms, in lung, diaphragm, mesenteric lymph nodes, intestine, and adrenal glands. Molecular analysis performed on DNA isolated from lung tissue, including conventional polymerase chain reaction (PCR) targeting the internal transcribed spacer region for the ribosomal RNA gene complex and real-time PCR targeting the gene encoding a unique region of M specific protein, identified the organism to be 100% identical to Histoplasma capsulatum with an average of 4.9 × 10(7) gene copies per gram of tissue. The present report describes histologic and molecular techniques for diagnosing histoplasmosis.

A survey of equine abortion and perinatal foal losses in Hungary during a three-year period (1998-2000)

Cases of equine abortion and perinatal foal losses were investigated in Hungary during a three-year period (1998-2000). Samples from aborted equine fetuses and newborn foals (total n = 96) were examined using bacteriological, virological, pathological, immunohistochemical (IHC), molecular biological and serological methods. The cause of abortion and perinatal foal loss was identified in 67/96 cases (70%); viral infection was found in 22 (23%), viral and bacterial coinfection in 1 (1%), bacterial infection in 23 (24%), protozoan infection in 1 (1%) and fungal infection in 2 cases (2%). Morphological lesions suggestive of infection were recorded in 2 (2%) and non-infectious causes in 16 cases (17%).

Klebsiella oxytoca as a cause of equine abortion--short communication

Klebsiella (K.) oxytoca infection induced the abortion of a female equine fetus in the 10th month of pregnancy. Bacteria were cultured from the liver, lung and stomach content. They were labelled with an anti-Mycobacterium bovis antibody in the thymus, liver and lungs and were stained with Giemsa and Brown-Brenn staining in the thymus and lung. The diffusely consolidated lungs contained numerous grey-whitish foci 2-4 mm in diameter, which corresponded to severe pyogranulomatous pneumonia characterised by numerous intraalveolar neutrophils and macrophages and multinucleated Langhans' giant cells. K. oxytoca was located in the cytoplasm of these cells, and extracellularly in the lumen of alveoli, bronchioles and bronchi, in the capsule of thymus and in the sinusoids of the liver. The results indicate that K. oxytoca can cause sporadic equine abortion.

Equine histoplasmosis presenting as a tumor in the abdominal cavity

A 3.5-year-old Thoroughbred mare presented at necropsy with a large mass at the root of the mesentery and multiple smaller mesenteric masses. The mucosa of the small intestine contained numerous raised nodules. Histologic examination revealed severe granulomatous mesenteric lymphadenitis and enteritis. Epithelioid macrophages and multinucleated giant cells frequently contained numerous intracytoplasmic yeast organisms, which were strongly positive on immunohistochemical staining when using a polyclonal antibody against Histoplasma spp. A diagnosis of abdominal histoplasmosis was made based on the gross, microscopic, and immunohistochemical findings.

Keratitis due to Histoplasma spp. in a horse

A 5-year-old Holsteiner gelding from Germany was presented 2 months after a whitish discoloration of the left cornea was observed. Cytologic examination revealed intra- and extracellular globular structures, up to 4 micro m in size, consisting of a central spherical deeply basophilic body surrounded by an unstained halo. The structures were morphologically consistent with Histoplasma spp. Infection with Histoplasma organisms is not endemic in Europe. Topical use of fluconazole was successful in eliminating Histoplasma organisms within 10 days of initiation of treatment.

Histoplasmosis in the lung of a race horse with yersiniosis

A 4-year-old female thoroughbred race horse died of acute peritonitis caused by necrotizing granulomatous duodenitis. Yersinia enterocolitica was immunohistochemically demonstrated in macrophages in granulomas developed in the duodenum, lung, liver and abdominal lymph nodes. The yeast-like fungi were found in the cytoplasmic vacuoles of macrophages in the lung that infiltrated into the granulomas and surrounding alveoli with congestive edema. The yeast-like fungi were positively stained by Gomori-Grocott chromic acid methenamine silver stain and immuno-histochemically stained with anti-histoplasma antibody. In this case, it was considered that granulomas formed in the duodenum, lung, liver and abdominal lymph nodes were primarily caused by Yersinia enterocolitica due to idiopathic weakening of the immune system. Yeast-like fungi immunohistochemically identified as histoplasmas secondarily infected the lung. This is the first case regarded as equine histoplasmosis capsulati in Japan.

Disseminated histoplasmosis in a sea otter (Enhydra lutris)

Disseminated histoplasmosis was diagnosed in a 4.75-year-old, captive female sea otter (Enhydra lutris). At necropsy, the liver was found to be markedly swollen, with many nodules (4-12 mm in diameter). Histologically, macrophages containing numerous intracellular yeast-like organisms were noted in the liver, spleen, lung and kidney. These organisms were labelled immunohistochemically with anti-histoplasma yeast antibody. Ultrastructurally, the yeast-like organisms, 2-4 microm in diameter, were found within membranous structures in the cytoplasm of macrophages. This is the first confirmed report of disseminated histoplasmosis in sea otters.