Histoplasmosis in Africa: Current perspectives, knowledge gaps, and research priorities

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.

Histoplasmosis: A systematic review to inform the World Health Organization of a fungal priority pathogens list

Histoplasmosis, a significant mycosis primarily prevalent in Africa, North and South America, with emerging reports globally, poses notable health challenges, particularly in immunocompromised individuals such as people living with HIV/AIDS and organ transplant recipients. This systematic review, aimed at informing the World Health Organization's Fungal Priority Pathogens List, critically examines literature from 2011 to 2021 using PubMed and Web of Science, focusing on the incidence, mortality, morbidity, antifungal resistance, preventability, and distribution of Histoplasma. We also found a high prevalence (22%-44%) in people living with HIV, with mortality rates ranging from 21% to 53%. Despite limited data, the prevalence of histoplasmosis seems stable, with lower estimates in Europe. Complications such as central nervous system disease, pulmonary issues, and lymphoedema due to granuloma or sclerosis are noted, though their burden remains uncertain. Antifungal susceptibility varies, particularly against fluconazole (MIC: ≥32 mg/l) and caspofungin (MICs: 4-32 mg/l), while resistance to amphotericin B (MIC: 0.125-0.16 mg/l), itraconazole (MICs: 0.004-0.125 mg/l), and voriconazole (MICs: 0.004-0.125 mg/l) remains low. This review identifies critical knowledge gaps, underlining the need for robust, globally representative surveillance systems to better understand and combat this fungal threat.

Histoplasma seropositivity and environmental risk factors for exposure in a general population in Upper River Region, The Gambia: A cross-sectional study

Robust surveillance of Histoplasma species is warranted in endemic regions, including investigation of community-level transmission dynamics. This cross-sectional study explored anti-Histoplasma antibody seroprevalence and risk factors for exposure in a general population in Upper River Region (URR), The Gambia. Study participants were recruited (December 2022-March 2023) by random household sampling across 12 Enumeration Areas (EAs) of URR. A questionnaire and clinical examination were performed; exploring demographic, clinical and environmental risk factors for Histoplasma exposure. One venous blood sample per participant was subject to IMMY Latex Agglutination Histoplasma test to determine presence of a recent IgM response to Histoplasma. Seropositivity risk factors were explored by multi-level, multivariable logistic regression analysis. The study population (n = 298) aged 5-83 years, demonstrated a positively skewed age distribution and comprised 55.4% females. An apparent seroprevalence of 18.8% (n = 56/298, 95% CI 14.5-23.7%) was measured using the LAT. A multivariable model demonstrated increased odds of Histoplasma seropositivity amongst female participants (OR = 2.41 95% CI 1.14-5.10); and participants reporting involvement in animal manure management (OR = 4.21 95% CI 1.38-12.90), and management of domestic animals inside the compound at night during the dry season (OR = 10.72 95% CI 2.02-56.83). Increasing age (OR = 0.96 95% CI 0.93-0.98) was associated with decreased odds of seropositivity. Clustering at EA level was responsible for 17.2% of seropositivity variance. The study indicates frequent recent Histoplasma exposure and presents plausible demographic and environmental risk factors for seropositivity. Histoplasma spp. characterisation at this human-animal-environment interface is warranted, to determine public health implications of environmental reservoirs in The Gambia. The study was supported by Wellcome Trust (206,638/Z/17/Z to CES) and a University of Liverpool-funded PhD studentship (to TRC).

Frequency of fungal pathogens in autopsy studies of people who died with HIV in Africa: a scoping review

BACKGROUND

Fungal infections are common in HIV-infected individuals and significantly contribute to mortality. However, a substantial number of cases are undiagnosed before death.

OBJECTIVE

To determine the frequency of fungal pathogens in autopsy studies of people who died with HIV in Africa.

METHODS

We conducted a scoping review of autopsy studies conducted in Africa.

DATA SOURCES

PubMed, Scopus, Web of Science, Embase, Google Scholar, and African Journal Online.

STUDY ELIGIBILITY CRITERIA

The review encompasses studies published from inception to September 2023, and no language restrictions were imposed during the search process. We included studies that reported histopathological or microbiological evidence for the diagnosis of fungal infections and other pathogens.

DATA SYNTHESIS

Data were summarized using descriptive statistics and no meta-analysis was performed.

RESULTS

We examined 30 articles reporting studies conducted between 1991 and 2019, encompassing a total of 13 066 HIV-infected decedents across ten African countries. In five studies, the autopsy type was not specified. Among those studies with specified autopsy types, 20 involved complete diagnostic autopsies, whereas 5 were categorized as partial or minimally invasive autopsies. There were 2333 pathogens identified, with 946 (40.5%) being mycobacteria, 856 (36.7%) fungal, 231 (3.8%) viral, 208 (8.9%) parasitic, and 92 (3.9%) bacterial. Of the 856 fungal pathogens identified, 654 (28.0%) were Cryptococcus species, 167 (7.2%) Pneumocystis jirovecii, 16 (0.69%) Histoplasma species, 15 (0.64%) Aspergillus species, and 4 (0.17%) Candida species. Other major non-fungal pathogens identified were cytomegalovirus 172 (7.37%) and Toxoplasma gondii 173 (7.42%).

CONCLUSIONS

Invasive fungal infections occur in over one-third of people who succumb to HIV in Africa. In addition to cryptococcosis and Pneumocystis jirovecii pneumonia, integrating other priority fungal pathogen detection and management strategies into the broader framework of HIV care in Africa is recommended. This involves increasing awareness regarding the impact of fungal infections in advanced HIV disease and strengthening diagnostic and treatment capacity.

Histoplasmosis in Solid Organ Transplantation

Histoplasma capsulatum, the etiological agent for histoplasmosis, is a dimorphic fungus that grows as a mold in the environment and as a yeast in human tissues. It has a broad global distribution with shifting epidemiology during recent decades. While in immunocompetent individuals infection is usually self-resolving, solid organ transplant recipients are at increased risk of symptomatic disease with dissemination to extrapulmonary tissue. Diagnosis of histoplasmosis relies on direct observation of the pathogen (histopathology, cytopathology, and culture) or detection of antigens, antibodies, or nucleic acids. All transplant recipients with histoplasmosis warrant therapy, though the agent of choice and duration of therapy depends on the severity of disease. In the present article, we describe the pathogenesis, epidemiology, clinical manifestations and management of histoplasmosis in solid organ transplant recipients.

Frequent and intense human-bat interactions occur in buildings of rural Kenya

Simultaneous use of domestic spaces by humans and wildlife is little understood, despite global ubiquity, and can create an interface for human exposure to wildlife pathogens. Bats are a pervasive synanthropic taxon and are associated with several pathogens that can spill over and cause disease in humans. Urbanization has destroyed much natural bat habitat and, in response, many species increasingly use buildings as roosts. The purpose of this study was to characterize human interactions with bats in shared buildings to assess potential for human exposure to and spillover of bat-borne pathogens. We surveyed 102 people living and working in buildings used as bat roosts in Taita-Taveta county, Kenya between 2021 and 2023. We characterized and quantified the duration, intensity, and frequency of human-bat interactions occurring in this common domestic setting. Survey respondents reported living with bats in buildings year-round, with cohabitation occurring consistently for at least 10 years in 38% of cases. Human contact with bats occurred primarily through direct and indirect routes, including exposure to excrement (90% of respondents), and direct touching of bats (39% of respondents). Indirect contacts most often occurred daily, and direct contacts most often occurred yearly. Domestic animal consumption of bats was also reported (16% of respondents). We demonstrate that shared building use by bats and humans in rural Kenya leads to prolonged, frequent, and sometimes intense interactions between bats and humans, consistent with interfaces that can facilitate exposure to bat pathogens and subsequent spillover. Identifying and understanding the settings and practices that may lead to zoonotic pathogen spillover is of great global importance for developing countermeasures, and this study establishes bat roosts in buildings as such a setting.

Colonic histoplasmosis

An Ivorian woman presented to us with a 2-month history of fever, abdominal pain and nausea. Human immunodeficiency virus serology was positive. Abdominal ultrasound showed enlarged abdominal lymph nodes and wall thickening of the right colon. Colonic biopsy was suggestive of fungal infection and polymerase chain reaction for Histoplasma capsulatum on biopsy was positive.

Histoplasmosis: An epidemiological and clinical update in China, review and a case report

Histoplasmosis is a systemic mycosis caused by the dimorphic fungus in the genus Histoplasma. Histoplasmosis is overlooked in China. This study aims to provide an epidemiological and clinical update on histoplasmosis in China by literature review. We reviewed cases of histoplasmosis reported in recent 11 years  and described a case of histoplasmosis-triggered hemophagocytic lymphohistiocytosis (HLH) in an immunocompetent patient. A total of 225 cases of histoplasmosis diagnosed in China between 2012 and 2022 were involved in this study, compared with 300 cases reviewed from 1990 to 2011, an increasing number of cases of histoplasmosis have been diagnosed in the last 11 years. The majority of cases of histoplasmosis were autochthonous cases, mainly from provinces Sichuan (56/225, 24.9%), Hunan (50/225, 22.2%), Guangdong (31/225, 13.8%), and Yunnan (24/225, 10.7%). Higher incidence (52.5%, 53/99) of histoplasmosis occurred in immunocompetent patients which is similar to those from the previous 21 years, and the prevalence of the disease did not vary highly over time. Of note, the number of histoplasmosis cases is increasing, and the geographic distribution is shifting southwards over time. Improved awareness is critically important for informing clinical practice in China.

Acute pulmonary histoplasmosis: a case series from an outbreak in Southeastern Brazil

Histoplasmosis is a systemic mycosis prevalent in the Americas. Humans become infected via the respiratory route by inhaling aerosols from soil contaminated with bird and bat excretions. Acute pulmonary histoplasmosis is usually asymptomatic and is more often a self-limiting illness. We report a series of seven acute pulmonary cases in adults during an outbreak in Nova Friburgo city, Rio de Janeiro State, Brazil, in a group of volunteers who were cleaning an old, abandoned house without using personal protective equipment. The patients had a favorable evolution after suitable treatment, but all required hospitalization.

Acute Peritoneal Histoplasmosis Mimicking Ovarian Cancer and Review of the Literature on Histoplasma Peritonitis

Peritoneal histoplasmosis is a rare entity with few cases reported in the literature. We present a case of isolated acute peritoneal histoplasmosis that mimicked an advanced ovarian malignancy in a patient undergoing antitumor necrosis factor therapy for rheumatoid arthritis. We also reviewed the literature on Histoplasma peritonitis.