Answer to May 2019 Photo Quiz

Answer: Disseminated Acanthamoeba infection. The biopsy of the palate lesion revealed ulcerated and necrotic tissues with the presence of protozoan parasites around blood vessels on H&E staining (see Fig. 1E and F in the photo quiz). Amoebic trophozoites were identified based on the presence of morphologic features (a well-defined cytoplasm membrane with a round nucleus with a prominent nucleolus surrounded by a clear zone and vacuolated cytoplasm and, in some cases, projections of the membrane called pseudopodia). Immunohistochemical staining using antibodies against Entamoeba spp. (a 1:200-diluted rabbit serum raised against two internal peptides in the heavy chain HGl2 of the Gal/GalNAc lectin [1]) was slightly positive on the tissues. In this context of immunodeficiency, the presence of Acanthamoeba was confirmed by using PCR on formalin-fixed and paraffin-embedded tissues. Sequence analysis of the Acanthamoeba Rns gene suggested that the isolate was related to the T4 genotype (GenBank accession no. MG020109) (2). The absence of Balamuthia mandrillaris, another amoeba responsible for skin lesions, was confirmed by PCR.

Acanthamoeba spp. are found as ubiquitous free-living amoebae in all types of water, soil, and air and can be isolated from nasopharynxes and stools of healthy humans (3). In the context of immunodeficiency, Acanthamoeba can cause a central nervous system infection called granulomatous amebic encephalitis or may disseminate to multiple organ systems. Disseminated infections usually occur in solid organ transplant recipients, AIDS patients, or patients with hematological malignancies (4). Acanthamoeba infections have rarely been reported to occur in lung transplant recipients, and to our knowledge, only nine other cases have been reported in this setting (5, 6). This infection is rare because it occurs in the context of both immunodeficiency and, probably, a particular epidemiology (e.g., frequent contact with water). Moreover, it is underdiagnosed because it is little known by physicians. Finally, it is misdiagnosed because the diagnosis is difficult (owing to a lack of specific clinical signs, the requirement of experienced pathologists, and the need for specific confirmatory biological tests).

Here, the presence of amoebae was suspected only postmortem and after several skin biopsies and one palate biopsy. In consequence, specific cultures were never performed for the isolation of Acanthamoeba.

The prognosis of Acanthamoeba infections is poor, and diagnosis is often made postmortem, as in our case. In tissues, the amoebae can be distinguished from host cells by their perivascular location and their prominent central nucleoli (3). However, identification of the amoebae at the genus level can be challenging when standard staining is used. Cysts of Acanthamoeba and B. mandrillaris can be observed but have similar morphologies. Immunohistochemical techniques are useful for detection and differentiation of the amoebae, but Acanthamoeba and B. mandrillaris antibodies are not widely available. Here, the Acanthamoeba trophozoites were immunostained with the Entamoeba antibodies. PCR can be useful for early and specific diagnosis of these infections; it can be performed directly in cerebrospinal fluid, bronchoalveolar lavage fluid, and tissues. Optimal treatment for disseminated acanthamebiasis is not well defined, although several drugs have been studied (7, 8).

Physicians, histopathologists, and biologists have to be aware of this rare and severe infection, and molecular detection of Acanthamoeba must be considered in immunocompromised patients with skin lesions and previous negative microbiological test results.

Data availability.

Sequence data were deposited in GenBank under accession no. MG020109.

See https://doi.org/10.1128/JCM.00087-18 in this issue for photo quiz case presentation.