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Veterinary research communications2024; 48(5); 3483-3487; doi: 10.1007/s11259-024-10483-0

An overview of various stages and morphology of Histoplasma capsulatum var. farciminosum in the horse.

Abstract: This article describes the development of the pathogenic dimorphic fungus Histoplasma capsulatum var. farciminosum (HCF), which is the causative agent of Equine epizootic lymphangitis (EEL), from the mycelial form in the soil to the yeast form in the horse. In this study, the stages and morphology of HCF were identified through histopathological analysis and culture with various samples collected in Ethiopia from 15 horses showing clinical signs of EEL. In equids, especially cart horses in Ethiopia, poor-quality harnesses cause cutaneous wounds, which often attract flies facilitating the transmission of the fungus. Also, HCF infection occurs through open wounds or ocular mucous membranes when horses roll on contaminated damp soil. Respiratory histoplasmosis can occur through inhaling fungal spores, which is rare. HCF microconidia enter the lungs and skin wounds and are phagocytized by tissue-resident macrophages. The spores undergo intracellular replication within the macrophages transitioning into yeasts. The infected macrophages undergo lysis releasing pathogenic yeast cells into the surrounding tissue. Consequently, yeast-rich purulent exudate is produced, contaminating the soil in stables where yeast cells germinate into the mycelial form, and the entire process starts from the beginning.
© 2024. The Author(s), under exclusive licence to Springer Nature B.V.
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Publication Date: 2024-08-20 PubMed ID: 39162765DOI: 10.1007/s11259-024-10483-0Google Scholar: Lookup
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Summary

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The research article discusses the evolution of Histoplasma capsulatum var. farciminosum (HCF), a fungus causing Equine epizootic lymphangitis in horses, and its various growth stages.

Collection and Analysis of Samples

  • The researchers collected samples from fifteen horses in Ethiopia who exhibited signs of Equine epizootic lymphangitis (EEL).
  • They conducted histopathological analysis and culture of these samples, allowing them to map the stages and morphology of HCF.

Causes and Transmission of Infection

  • The study noted that poor-quality harnesses in use for cart horses cause skin wounds, which flies are attracted to. This sets up conditions for the transfer of the HCF fungus.
  • Further, horses rolling on damp soil contaminated with the fungus could get infected through open wounds or ocular mucous membranes.
  • They also identified a less common route of infection – horses inhaling fungal spores, causing respiratory histoplasmosis.

Infection and Replication Process

  • The HCF microconidia (spores) infiltrate into the lungs and skin wounds and are engulfed by tissue-resident macrophages – a type of white blood cell in the immune system.
  • Following this, the spores undergo replication within the macrophages and transmogrify into yeasts.
  • Eventually, these infected macrophages break down, setting free pathogenic yeast cells into the surrounding tissues.
  • This, in turn, leads to the creation of a yeast-rich purulent exudate (an oozing fluid).

Recurrence and Continuation of Infection Cycle

  • This purulent exudate contaminates the soil in the stable.
  • The yeast cells present in the fluid germinate into a mycelial form (a vegetative part of a fungus) in the soil.
  • This triggers the start of the entire HCF life cycle again, setting conditions for a new round of infection.

In essence, the study reported the detailed life cycle of HCF in horses, leading to a better understanding of the transmission and manifestation of Equine epizootic lymphangitis.

Cite This Article

APA
Al Mheiri FG, Joseph M, Joseph S, Alqassim M, Kinne J, Wernery U. (2024). An overview of various stages and morphology of Histoplasma capsulatum var. farciminosum in the horse. Vet Res Commun, 48(5), 3483-3487. https://doi.org/10.1007/s11259-024-10483-0

Publication

Veterinary research communications
ISSN: 1573-7446
NlmUniqueID: 8100520
Country: Switzerland
Language: English
Volume: 48
Issue: 5
Pages: 3483-3487

Researcher Affiliations

Al Mheiri, Fatma Graiban
  • Clinical Department for Small Animals and Horses, University of Veterinary Medicine, 1210, Vienna, Austria.
  • Central Veterinary Research Laboratory, P.O. Box 597, Dubai, United Arab Emirates.
Joseph, Marina
  • Mycology, Bacteriology, Central Veterinary Research Laboratory, P.O. Box 597, Dubai, United Arab Emirates.
Joseph, Sunitha
  • Virology, Central Veterinary Research Laboratory, P.O. Box 597, Dubai, United Arab Emirates.
Alqassim, Mohammad
  • Central Veterinary Research Laboratory, P.O. Box 597, Dubai, United Arab Emirates.
Kinne, Joerg
  • Pathology, Central Veterinary Research Laboratory, P.O. Box 597, Dubai, United Arab Emirates.
Wernery, Ulrich
  • Mycology, Bacteriology, Central Veterinary Research Laboratory, P.O. Box 597, Dubai, United Arab Emirates. cvrl@cvrl.ae.
  • Central Veterinary Research Laboratory, P.O. Box 597, Dubai, United Arab Emirates. cvrl@cvrl.ae.

MeSH Terms

  • Horses
  • Animals
  • Histoplasma / physiology
  • Histoplasma / isolation & purification
  • Horse Diseases / microbiology
  • Horse Diseases / pathology
  • Histoplasmosis / veterinary
  • Histoplasmosis / microbiology
  • Histoplasmosis / pathology

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This article includes 17 references
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Citations

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