Pereira Filho reported a case of lobomycosis among the Kaiabi in 1957 (12,16), and Nery-Guimarães reported another in 1964 (12,17). Since then, many cases in have been reported among this population in the medical literature. The high prevalence of lobomycosis in this population is a notable epidemiologic finding in medical ethnography (18). The disease is so prevalent that, since 1915, references have been made to a Kaiabi-associated skin disease, called piraip in the Kaiabi language, a branch of the Tupi-Guarani linguistic family.

The prevalence of lobomycosis in the Kaiabi has been declining over time. Changes in the geographic region in which they live after many Kaiabi moved 400 km east to the XIP, changes in cultural behavior, a lack of fungal agents in the new ecosystem, and changes in the immunity of this population are some hypotheses that could explain the reduction in this prevalence. Before moving to the XIP, all Kaiabi reported with lobomycosis lived in the Arinos River or Teles Pires River regions. No new cases have occurred in Kaiabi who have only lived in XIP. The environment of the XIP is similar to Arinos River or Teles Pires River regions, but the regions have distinct watersheds.

Lobomycosis also occurs in some species of estuarine, inshore cetaceans (Tursiops truncates) and offshore cetaceans (Sotalia guianensis) (19–21). Clinical and phenotypic features of the uncultivated agent of the disease in dolphins suggested that this pathogen was the same organism, L. loboi. However, molecular data suggest that the cause of cutaneous lesions in dolphins is a novel strain of P. brasiliensis, P. brasiliensis var. ceti (22,23). Moreover, a lobomycosis-like disease among bottlenose dolphins has been reported (24). Bermudez et al. (25) hypothesized that the marine environment could be a source of the fungus in a human case they reported. Some cetaceous species inhabit the rivers of the Amazon region, including Sotalia fluviatilis dolphins in the Orino River in Venezuela and Inia geoffrensis dolphins, known as boto, in the Amazonas River in Brazil. However, these animals do not inhabit the XIP rivers, and lobomycosis has never been identified in these animals (19). Curiously, 1 case in Africa and 1 in Greece were reported in persons who had never traveled to South or Central America (15,26). These cases might support water as the environmental source of this fungus, but evidence of dolphin–human transmission has been weak.

Of the 63 cases of lobomycosis among the Kaiabi, most patients were male, but female Kaiabi also had a high prevalence of the disease. Early reports indicated that 32% of lobomycosis case-patients among the Kaiabi were female. Among nonindigenous women and girls, the disease occurrence ranged from 10%–12% (27). In addition, the increased prevalence in female Kaiabi might be because they work in close contact with the environment during activities such as small-scale farming.

Medical reports have shown that the age of onset of the disease is typically 20–40 years of age. However, most Kaiabi case-patients began to exhibit the disease before 21 years of age. The earliest onset we noted was at 1 year of age. The susceptibility and early onset of lobomycosis among Kaiabi children can be explained by their precocious contact with wood and soil.

Some researchers have proposed different clinical classifications for lobomycosis. For their analysis, Baruzzi et al. (11) adopted a modified classification, involving a localized form and multicentric form. The multicentric form is unusual and infrequent among nonindigenous populations. Other authors reported 41 cases with multicentric forms among 249 cases in nonindigenous populations (27). However, among the Kaiabi, the multicentric form was more common than the localized form. In analyzing the classification for sex, we noted that manifestations of the disease are quite distinct in male and female Kaiabi (Table 2). The multicentric form was more frequently seen in male case-patients and the localized form was more frequent in female case-patients.

Cellular immunodeficiency is possible in cases of lobomycosis (28). Different host immune responses against the fungus or relatively high exposure to the fungal agent are possible explanations for the high incidence of lobomycosis among female case-patients. However, hormonal factors could be responsible for the protection against disease dissemination in females.

When reviewing anatomic locations of lesions, we noted that nonindigenous people more frequently have lobomycosis lesions on the outer ear. However, among the Kaiabi population, only 2 case-patients had lesions on the outer ear and many more lesions were noted on the limbs and truck. A possible reason is a variation in behavior. Nonindigenous groups tend to carry heavy burdens on their shoulders, but the Kaiabi tend to carry wood and other materials on their heads and backs. In addition, the Kaiabi do not wear shirts, so the skin of the upper body is exposed and could be exposed to the causative agent in materials they carry. The prepuce lesion was a rare localization found in 1 case.

We based our analysis on data collected by physicians who visited the XIP for >45 years. Among the Kaiabi, most of the patients with localized lobomycosis did not develop new lesions over time, but 44.1% of patients with the multicentric form had new lesions over time. Patients reported that recurrent ulcerations impaired their quality of life, and patients with the multicentric form had periods of ulcerations more frequently than those with the localized form. We did not observe any change in ulcer healing or worsening related to weather or seasons of the year. Among all lobomycosis cases worldwide, 4 reports of progression to squamous cell carcinoma have occurred; 2 were in the Kaiabi population, and both died from metastasis (8). Outside of the Kaiabi population, no deaths from complications of lobomycosis have been reported. In addition, among indigenous populations living in the XIP, lobomycosis greatly affects quality of life; those who have it are stigmatized, and the disease has been known as Kaiabi leprosy in the past.

Treatment is a challenge, and systemic drugs are not effective (29). However, many treatment attempts have been reported in some case-patients. The medical literature reports some isolated positive results with itraconazole, clofazimine, leprosy multidrug therapy, or posaconazole (27,30). Other approaches, such as surgical excision, cryosurgery, and electrosurgery, should be considered in addition to drug treatment. However, no known effective treatment for lobomycosis, especially the multicentric form, has been found (30). Among the Kaiabi, treatment by surgery was successful in some localized cases without recurrence in a 30-year follow-up.

In conclusion, lobomycosis is a rare disease that affects certain geographic regions, especially in countries with low socioeconomic status (31), but its prevalence among the Kaiabi population in Brazil is exceptionally high. The 63 cases we identified among this population represent 11.5% of all cases of lobomycosis known in the world since the disease was identified. Our clinical and epidemiologic analysis shows cases among the Kaiabi have particular characteristics, including a high incidence of female case-patients, early onset in persons <21 years of age, a high incidence of the multicentric form in male case-patients, and a high incidence of the localized form in female case-patients. Little is known about the prevalence of lobomycosis and the effective treatment remains a challenge, especially for the multicentric form. Phylogenetic analysis of L. loboi could help in the development of treatments for this fungal infection.