Molecular characterization of Histoplasma capsulatum isolated from an outbreak in treasure hunters Histoplasma capsulatum in treasure hunters

Abstract

Background: In Mexico, primary pulmonary histoplasmosis is the most relevant clinical form of the disease. The geographical distribution of specific strains of Histoplasma capsulatum circulating in Mexico has not been fully established. Outbreaks must be reported in order to have current, updated information on this disease, identifying new endemic areas, manner of exposure to the fungi, and molecular characterization of the causative agents. We report a recent outbreak of histoplasmosis in treasure hunters and the molecular characterization of two isolates obtained from these patients.

Methods: Six patients admitted to the National Institute of Respiratory Diseases (INER) in Mexico City presented severe respiratory symptoms suggestive of histoplasmosis. They acquired the infection in the Veracruz (VZ) endemic zone. Diagnosis was made by X-ray and Computed tomography (CT), liver function, immunological techniques, and culture. Identification of H. capsulatum isolates was confirmed by using Polymerase chain reaction (PCR) was conducted with a probe from the M antigen, and the isolates were characterized by means of Random amplification of polymorphic DNA (RAPD)-PCR employed the 1253 oligonucleotide and a mixture of oligonucleotides 1281 and 1283. These were compared to eight reference strain isolates from neighboring areas.

Results: X-ray and CT revealed disseminated micronodular images throughout lung parenchyma, as well as bilateral retrocaval, prevascular, subcarinal, and hilar adenopathies, hepatosplenomegaly, and altered liver function tests. Five of the six patients developed disseminated histoplasmosis. Two H. capsulatum strains were isolated. The same band profile was detected in both strains, indicating that both isolates corresponded to the sole H. capsulatum strain. Molecular characterization of the isolates was similar in 100% with the EH-53 Hidalgo human (HG) strain (reference strain integrated into the LAm A clade described for Latin America).

Conclusions: The two isolates appeared to possess the same polymorphic pattern; they are indistinguishable from each other and from EH-53. It is important to remain updated on recent outbreaks of histoplasmosis, the manner of exposure to the fungi, as well as the molecular characterization of the isolates. The severity of cases indicates that this strain is highly virulent and that it is probably prevalent in Hidalgo and Veracruz states.

Figure 1

Ciudad Cardel, La Antigua Municipality, Veracruz, Mexico. The figure shows, the Veracruz-neighboring states, endemic areas from which isolates and type strains and, Mexico City (MC) and Naucalpan (patient's place of residence).

Figure 2

Identification and characterization of Histoplasma capsulatum isolates from Veracruz (VZ). (a) Identification of H. capsulatum isolates using Polymerase chain reaction (PCR) with the probe designed from the M antigen; (b and c) characterization by Random amplification of polymorphic DNA-PCR (RAPD-PCR) of H. capsulatum isolates with 1253 (b) and the mixture of 1281 and 1283 oligonucleotides (c); M 100 bp DNA Ladder; LFD, EVP, and EH-317 H. capsulatum; C (-) reagent control. (d) RAPD-PCR DNA patterns obtained from H. capsulatum isolates LFD and EVP compared with isolated 8 reference strains from humans or bats from different geographical regions in Mexico.

Figure 3

Dendrogram constructed from the molecular profiles. Genetic similarity among Histoplasma capsulatum isolates from Veracruz (VZ) with isolates from other neighboring endemic zones, in Mexico.