Histoplasmosis

Project and Seminar Material for Microbiology

Abstract

Histoplasmosis is the most prevalent endemic fungal infection in certain parts of the world like in North America. The clinical spectrum ranges from asymptomatic, self-limited illness to a life-threatening progressive disseminated disease. Chronic manifestations of healed infection can also be problematic. Clinical presentation depends on the infectious load, underlying immune status, and lung function.

The preferred diagnostic methods and treatment options vary with clinical scenario and severity of illness. New diagnostic tools and treatment options are now available in clinical practice. This paper presents an overview of this important endemic mycosis with emphasis on diagnosis and treatment recommendations for the different clinical syndromes of histoplasmosis.

Table Of Content

Preliminary Page(s)

Title page
Certification page
Dedication
Acknowledgement
Abstract
Table of content

Chapter One

1.0 Introduction

1.1 Background of the Study
1.2 Statement Problem
1.3 Research Objective

Chapter Two

2.0 Review Of Related Literature

2.1 Epidemiology
2.2 Pathogenesis
2.3 Clinical Manifestation and Treatment

Chapter Three

3.0 Issues And Gaps

3.1 Manifestations Requiring Antifungal Therapy
3.2 Chronic Manifestations that Do Not Require Antifungal Therapy

Chapter Four

4.0 Conclusion

4.1 Conclusion
4.2 Recommendation
References

Chapter One

1.0 Introduction

1.1 Background Of The Study

Histoplasmosis was first described a little over a century ago by an American physician, Samuel Darling, who was working in the Canal Zone in Panama. He described the disseminated form of the disease in a fatal case from Martinique (19). It took decades to prove that Histoplasma capsulatum is a dimorphic fungus, that histoplasmosis is primarily a pulmonary disease, and that the environmental reservoir is soil (25, 33). There are two varieties of H. capsulatum that are pathogenic to humans, H. capsulatum var. capsulatum and H. capsulatum var. duboisii, and a third variety that is an equine pathogen, H. capsulatum var. farciminosum (23). H. capsulatum var. duboisii exists in Africa, and cases have been reported in both Africa and Europe, when patients from Africa seek care there.

This review will focus solely on disease manifestations of H. capsulatum var. capsulatum, hereafter referred to as H. capsulatum. H. capsulatum exists as a mold in the environment and forms a white to tan colony on Sabouraud dextrose agar at 25 to 30°C. Two types of conidia are formed. The macroconidia or tuberculate conidia are 8 to 15 m in diameter and have a thick wall with distinctive projections on the surface; the microconidia are tiny, smooth structures that are 2 to 4 m in diameter and are the infectious form. At 37°C in vitro and in tissues, the organism converts into the yeast phase that is composed of tiny 2- to 4-m oval budding yeasts that are found both inside and outside macrophages. The organism is not encapsulated, although in tissues, it appears to be surrounded by a clear zone that was misinterpreted as being a capsule by Darling (19).

H. capsulatum occurs most commonly in North America and Central America, but the organism exists in many diverse areas around the world (13). In the United States, H. capsulatum is endemic in the Mississippi and Ohio River valleys and also exists in localized foci in many mideastern states. Soil containing large amounts of bird or bat guano especially that found under blackbird roosts or next to chicken coops, supports luxuriant growth of the mold (11). Once contaminated, soil yields H. capsulatum for many years after birds no longer roost in the area. Caves can be highly contaminated by H. capsulatum that thrives on the bat guano (27).

1.2 Statement Problem

Infection with H. capsulatum occurs during day-to-day activities in areas where H. capsulatum is highly endemic or in the course of occupational and recreational activities that disrupt the soil or accumulated dirt and guano in old buildings, on bridges, and in caves where bats have roosted (11, 59). Outbreaks that involve anywhere from a handful to tens of thousands of individuals have been described. Every year, hundreds of thousands of individuals in the United States and Central America are infected with H. capsulatum.

Most do not realize that they have had a fungal infection. The true extent of infection with H. capsulatum in the Ohio and Mississippi River valleys was defined only after the development of a skin test antigen that could be used in epidemiological studies (12). The seminal studies by Christie and Peterson and Palmer established the relationship of histoplasmin skin test positivity to pulmonary calcifications in tuberculin-negative persons (12, 95). Subsequent large-scale population studies by the Public Health Service defined the area where H. capsulatum is endemic (32) and demonstrated that over 80% of young adults from the states bordering the Ohio and Mississippi Rivers had been previously infected with H. capsulatum.

1.3 Research Objective

The objective of this seminar is to focus on the clinical, diagnostic, and therapeutic aspects of histoplasmosis.

Chapter Four

4.0 Conclusion

4.1 Conclusion

Histoplasmosis is an endemic infection in most of the United States and can be found worldwide. The spectrum of this illness ranges from asymptomatic infection to severe disseminated disease. Life-threatening illness is usually associated with an immune-compromised state; however, 20 percent of severe illnesses result from a heavy inoculum in healthy persons. Culture remains the gold standard for diagnosis but requires a lengthy incubation period. Fungal staining produces quicker results than culture but is less sensitive. Testing for antigen and antibodies is rapid and sensitive when used for particular disease presentations. An advantage of antigen detection is its usefulness in monitoring disease therapy. Antifungal therapy is indicated in chronic or disseminated disease and severe, acute infection. Treatment of histoplasmosis depends on the severity of the clinical syndrome. Mild cases may require only symptomatic measures, but antifungal therapy is indicated in all cases of chronic or disseminated disease and in severe or prolonged acute pulmonary infection. Treatment should be continued until all clinical findings have resolved and H. capsulatum antigen levels have returned to normal. In patients with acquired immunodeficiency syndrome (AIDS), lifelong suppressive therapy is required to prevent relapse. In immune-competent patients with acute pulmonary disease and respiratory compromise, corticosteroids may be helpful as adjunctive therapy.

4.2 Recommendation

Based on the findings, it is recommended that since both natural variation within the species and the capacity of individual organisms adapt to make the fungus a widespread and successful pathogen, there s need to treat environmental surfaces and areas to eliminate contamination.