African Histoplasmosis - Causes, Clinical Features, Diagnosis, Prevention, and Treatment

Introduction:

Millions of species of fungi cause infection in humans. They are widespread, and only some of these infections are serious and sometimes even fatal. Fungal infections are primarily opportunistic, meaning that the infections occur in patients with a compromised immune system. Advanced treatments like antibiotics, steroids, and immune-compromising agents have increased opportunistic fungal infections. Fungal infections can affect superficially (involving skin) or systemically (involving other organ systems). Although fungal infections are globally prevalent, the African continent carries the burden of fungal infections due to endemicity. African histoplasmosis is one such fungal infection native to the African subcontinent.

What Is African Histoplasmosis?

African histoplasmosis is a fungal infection reported mainly in the African subcontinent. It is caused by a fungus called Histoplasma capsulatum var. duboisii. It is an intracellular fungal infection, where the fungus invades and replicates inside the cells. The Histoplasma fungus causing African histoplasmosis is common in central and west Africa, including the Madagascar islands. The disease mainly affects the skin and the bones; the involvement of other organs can be seen in rare cases. African histoplasmosis causes infection in otherwise healthy individuals or an opportunistic infection in AIDS (acquired immune deficiency syndrome) and other immune-compromised conditions.

What Causes African Histoplasmosis?

The exact mechanism of the disease manifestation is not fully understood. The fungus can reach the lungs through direct inhalation. The fungus is said to spread to other organs through the bloodstream from the lungs. The portal of entry can also be through inoculation on the skin. According to reports, bat intestines carry the fungus, and soil mixed with bat excreta is thought to be a natural reservoir of the fungus. The endemic areas are located near these bat caves harboring fungus in their intestines. Some researchers are also suspecting insect bites to be the mode of transmission.

How Common Is African Histoplasmosis?

The disease has been detected in 20 African countries, with a majority of the cases reported from the countries located near the equator. It is common in regions with heavy rainfall and humidity. Some cases have been reported in the US, Europe, and South America. From the available data, it is known that males are affected more than females at a ratio of 2:1. The disease affects almost all age groups from 2 to 70 years. Although, a vast number of cases occur in the second decade of life. People engaged in outdoor activities like agricultural workers and carpenters are affected more. The African histoplasmosis can be asymptomatic and therefore goes undiagnosed and lacks epidemiological data. The WHO (world health organization) has classified this disease under the neglected tropical diseases list.

What Are the Clinical Features of African Histoplasmosis?

The disease manifests in the outer and deeper layers of the skin, lymph nodes, and bones.

A. Skin:

• On the skin, it is characterized by nodules and papules (raised areas in the skin) surrounded by a hyperpigmented border.

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• These papules and nodules enlarge and ulcerate at the center. The dead tissue may remain at the site of infection.

• The presentation can resemble psoriatic or eczematoid (eczema-like) skin lesions.

• Deeper skin lesions occur in the form of an abscess with pus or a granuloma (a small area of inflammation).

• The abscesses may cause pain. In later stages, abscess breaks open to discharge pus containing yeast cells of the fungus.

B. Bone:

• The involvement of the bone marrow is a striking sign of the disease.

• The dissolution of the bones (osteolytic) is quite common and involves multiple bones.

• Common sites of osteolytic lesions include the skull, ribs, vertebrae, thigh bone, and wrist.

• Bone dissolution in the skull causes a punched-out effect. Cases involving the skull show neurological complications.

• Granulation tissues can compress the spinal cord causing paralysis of the lower body.

• The lesions can resemble the changes occurring in bone cancer.

• Sometimes, the inner layers of the bone may get involved leading to pain and tenderness.

• Extension of bone lesions into the deeper tissues leads to abscess formation.

• Joints may get involved resulting in osteoarthritis.

C. Lymph Nodes:

• Lymphadenopathy (enlargement of the lymph nodes) at the site of infection is common.

D. Other Organs:

• If the lungs are involved, coughing with sputum production is common. Lesions of the lungs can resemble tuberculoid (tuberculosis-like) changes.

• Gastrointestinal involvement shows dome-shaped nodules on the oral cavity and tongue mucosa. However, involvement of the gastrointestinal tract is extremely rare.

• Ocular lesions in the form of infection of the lacrimal gland, swelling can be rarely seen.

• General symptoms like fever, malaise, diarrhea and abdominal pain are common.

How Is African Histoplasmosis Diagnosed?

The diagnosis of histoplasmosis is made after definitive laboratory examinations. Skin lesions in the form of pus and abscesses demonstrate the fungus's presence. A biopsy can be performed to confirm the diagnosis. Bone lesions also contain the organism. The fungus can be recovered by inoculating clinical material by using laboratory media.

How to Prevent African Histoplasmosis?

Generally, histoplasmosis infection can be prevented by avoiding activities like soil digging where there are bat droppings, cleaning chicken coops, exploring caves near the endemic areas. A professional agency should be employed to clean large amounts of bat or bird excreta. People with immune-compromised conditions like AIDS, organ transplants, steroids, or chemotherapy recipients should take extra care.

What Is the Treatment for African Histoplasmosis?

The treatment of African histoplasmosis is a challenge due to the lack of availability of medical facilities in the African continent. Patients with only skin lesions recover spontaneously. Additionally, surgical removal of the lesions is carried out. The lesions heal spontaneously without further complications. Patients who have systemic involvement need antifungal therapy. Amphotericin B is the drug of choice, and it is given for several weeks. The medication is delivered through an intravenous (IV) route for better efficacy. Other antifungal medications like Clotrimazole, Fluconazole, and Ketoconazole can successfully treat African histoplasmosis. Unfortunately, many of these drugs are out of reach for the people in Africa.

Is African Histoplasmosis Contagious?

No, the histoplasmosis infection is non-contagious. It cannot spread from an infected person to a healthy individual.

Conclusion:

African histoplasmosis is a fungal infection caused due to Histoplasma capssulatum vir. duboisii. The disease is endemic in African countries. This fungus affects skin, bone, lymph nodes, and rarely lungs. Skin lesions include ulcerated nodules, papules, and abscesses. Bone dissolution can occur in multiple sites. Most symptoms resolve spontaneously, but antifungal therapy must be carried out. Intravenous (IV) Amphotericin B is the drug of choice. Due to the lack of medical facilities and awareness, African histoplasmosis is often ignored or left undiagnosed.