AIDS-associated Talaromyces marneffei central nervous system infection in patients of southwestern China

Talaromyces marneffei (T. marneffei, also known as Penicillium marneffei) is a regional opportunistic fungus that mainly causes life-threatening disseminated infection in acquired immunodeficiency syndrome (AIDS) that causes epidemics in southeast Asia [1] and south China [2, 3]. It is estimated that approximately 50,000 HIV-positive patients are infected with T. marneffei every year in high-risk areas [4], and the incidence is likely to increase every year [5]. The thermally dimorphic fungi mainly invade skin, lungs, liver, spleen, lymph nodes and the circulatory system. Infection involving the central nervous system (CNS) is extremely rare. Currently, only 22 cases of AIDS-associated T. marneffei CNS infection and two sporadic cases of non-AIDS patients with T. marneffei CNS infection have been reported worldwide [6‐9]. These two non-AIDS patients suffered from T. marneffei CNS infections without any underlying immune deficiency diseases [7, 8]. Yet the mortality rate can be as high as 81% if diagnosis and treatment are delayed [9]. However, the clinical features of AIDS-associated CNS infection by T. marneffei are still unexplored. Here, we conducted a retrospective study on ten patients in southwestern China who were affected with AIDS-associated CNS infection by T. marneffei to characterize the clinical features and successful treatment of the disease.

Ten patients were admitted to Yunnan Provincial Infectious Diseases Hospital from January 2009 to December 2015. T. marneffei fungi were isolated from CSF from all 10 AIDS patients. Sabouraud dextrose agar (SDA) was used for T. marneffei culture medium. We excluded other CNS infections (bacteria, viruses, and other fungi). These patients underwent smear examination, fungal culture and acid-fast bacillus culture, and no cryptococcus and tubercle bacillus were found in the blood and CSF. Serological experiments for syphilis and HSV-1/2 antibody in both blood and CSF were also negative. At the same time, we collected the data on clinical manifestations, imaging and laboratory examinations, therapeutic regimens and outcomes of all ten patients for analysis. This study was approved by the Ethical Committee of the First Affiliated Hospital of Kunming Medical University.

Categorical variables are presented as a percentage (%). The normal distribution data are expressed as the mean ± standard deviation (\(\overline{\text{x}} \pm {\text{s}}\)). Nonnormally distributed data are represented by median (interquartile range [IQR]). The CD4⁺ T cell counts of the deceased and surviving patients were nonnormally distributed, and the Mann–Whitney U test was used for comparison. Data analysis was performed using SPSS 22.0 software (SPSS Inc).

Disseminated T. marneffei infection mainly involves the circulatory, respiratory and digestive systems, resulting in common clinical symptoms, including fever, cough, abdominal pain, weight loss, anemia, and cutaneous lesions [10]. However, CNS involvement is rare. In this study, besides the common symptoms such as fever, anemia and skin lesions, all the patients predominantly showed initial presenting symptoms or manifestations of CNS infection, including headache, vomiting, dizziness and dyskinesia or fatigue. Severe patients presented with altered consciousness, such as drowsiness, loss of consciousness, convulsions or coma. Other signs the patients had included decreased lower limb muscle strength and neck rigidity, which were associated with intracranial hypertension. We reviewed previous sporadic cases, which also showed the typical symptoms of CNS T. marneffei infection among the patients with or without HIV infection [6‐8]. Wu et al. [8] reported a very rare case of a non-AIDS patient with T. marneffei CNS infection who had hearing loss and diplopia, which may be due to yeast infiltration of the optic and acoustic nerves; they suggested that if patients have hearing loss, this disease also needs to be considered. However, Le et al. [9] reported that the symptoms among 21 patients under their study were mostly fever (90%), anorexia (57%), fatigue (52%), cough (33%), and diarrhea (29%) and that only 10 cases (47%) showed initial symptoms of acute CNS infection, while symptoms of increased intracranial pressure and meningismus were absent in the others, which was very different from our study.

The common clinical manifestations of CNS fungal infections vary from chronic meningitis or meningoencephalitis or abscesses to a fungal ventriculitis [11]. We found that the majority of our patients had abnormal neuroimaging findings, mainly manifested as ventricular dilatation and intracranial infectious lesions, and half of them had pulmonary lesions. Combined with other reports of bilateral lateral ventricular hydrocephalus and intracranial infection lesions [6‐8], we are assured that the central nervous system lesions caused by T. marneffei are mainly meningitis. The existing study found that ventriculomegaly is a frequent finding in the neuroimages of patients with advanced HIV/AIDS disease due to HIV encephalopathy with cerebral atrophy [12]. However, the pathophysiology of T. marneffei invading the blood–brain barrier is still unclear. Additionally, we observed elevated CSF intracranial pressure, increased leukocyte count, low CSF glucose, low CSF chloride and high CSF protein levels in our study, which were consistent with previous case reports [6, 8, 9]. Low CSF glucose level may be related to glucose utilization by microorganisms, and the degree of hypoglycemia is directly correlated with the inflammatory process [13]. A previous study speculated that the low CSF glucose level can be used as a marker for the diagnosis of microbial meningitis [14]. Our results showed that the CSF profile of AIDS-associated T. marneffei CNS infection is extremely similar to those of other types of fungal meningitis, especially cryptococcal meningitis. This condition can be easily confused since cryptococcal meningitis is also a common opportunistic infection in HIV patients.

Talaromyces marneffei mainly infects immunocompromised individuals such as AIDS patients, particularly when individuals have CD4⁺ T cell counts < 50 cells/μL [15]. Studies have found that CD4⁺ T cells were usually below 50 cells/μL in HIV-associated cryptococcal meningitis and that some severe cases even had levels below 30 cells/μL [16, 17]. However, we observed that the median CD4⁺ T cell counts were 104 cells/μL, and three patients’ CD4⁺ T cells were above 200 cells/μL. Patients with relatively high levels of CD4⁺ T cells who also present with T. marneffei CNS infection may be due to subclinical infection of T. marneffei when patients’ CD4⁺ T cell counts was low, these patients develop unmasking immune reconstitution inflammatory syndrome (unmasking IRIS) after initial ART [18]. We assured that patients in epidemic areas have relatively higher CD4⁺ T cells, they should also be alerted to T. marneffei CNS infection. In addition, patients No. 8, 9, and 10, who eventually deceased, had very low CD4⁺ T cell counts (10, 63 and 40 cells/μL, respectively), especially patient No. 8, who died due to deterioration during hospitalization. Le et al. [9] also reported that the median CD4⁺ T cell counts of dead patients were 11 cells/μL in AIDS-associated T. marneffei CNS infection. We supposed that low CD4⁺ T cell counts may be associated with high mortality.

Currently, the recommended treatment for AIDS-associated T. marneffei non-CNS infection is intravenous AmB for 2 weeks followed by oral itraconazole (400 mg/day) for 10 weeks, then followed by oral itraconazole (200 mg/day) as maintenance therapy, with ART started as soon as possible [19, 20]. Considering the penetration of the blood–brain barrier, the concentration of the drug in the blood–brain and the long duration of illness, most patients initiated and prolonged anti-fungal therapy with AmB and itraconazole for maintenance therapy. However, patient No. 8, who died during hospitalization before confirmed T. marneffei infection, had received empirical antifungal fluconazole therapy. Patient No. 9 had improved clinically but died after a year of discharge, he only received initial treatment and lacked maintenance treatment. Patient No. 10, who had been treated with fluconazole for both initial and maintenance therapy, had improved clinically, but eventually died after half a year of discharge. Both patients were more likely to die of recurrence of T. marneffei infection. AmB has fungicidal activity and is superior to fluconazole, itraconazole, and voriconazole against T. marneffei, although they can treat HIV-associated fungus infection effectively [21‐23]. Moreover, AmB or liposomal amphotericin B (LipAmB) are the most common and successful antifungal drugs for CNS fungal infections, although these drugs have generally low or unmeasurable levels in the CSF. A study recommended that an AmB/LipAmB + 5FC regimen should be used as a first choice to treat cryptococcal meningitis in patients [24]. In our study, we also suggest that AmB is preferred for initial therapy and extension of the initial course until cerebrospinal fluid fungus cultures become negative, which can be more than 2 weeks as recommended in cases of cryptococcal meningitis [19]. Then, maintenance treatment should be continued with itraconazole until CD4⁺ T levels increase to more than 200 cells/μL. Then, there arises a thought-provoking question about when to start ART. Delayed ART may affect fungal clearance and immune system recovery. Early initiation of ART within the first 2 weeks of antifungal therapy may paradoxically induce IRIS in cases of cryptococcal meningitis [25‐27]. Thus, the initiation of ART should be based on fungal load, CD4⁺ T cell counts and the CSF fungal culture report after 2 weeks of therapy [28, 29]. Thus, a more rational management of HIV/AIDS coinfection with T. marneffei CNS infection needs to be further investigated.

Last, in our study, 7 out of 10 patients were farmers from different areas. The occupational relationships with the disease have not been reported by any other studies. The exact etiology of T. marneffei infection is not yet clear. Thus far, bamboo rats are believed to be the only reservoir of T. marneffei. Chariyalertsak et al. [30] identified agricultural exposure to soil during the rainy season as an important risk factor for T. marneffei infection. Therefore, farmers have high probability of contact exposure to the soil-exposed T. marneffei fungal spores and soil-burrowing bamboo rats.

To the best of our knowledge, we are the first to comprehensively report the clinical manifestations and laboratory characteristics of AIDS-associated T. marneffei CNS infection. In HIV/AIDS and T. marneffei epidemic areas, when patients exhibit symptoms and signs of acute nervous system infection or even show any neurological symptoms, they should be investigated for CSF fungal culture and given a brain imaging examination to make a comprehensive diagnosis. In the routine investigation of CSF, viral investigations, bacterial culture and fungus culture should be carried out under different temperature and time durations, as T. marneffei grows slowly in culture media. Notably, it is also necessary to rule out cryptococcal meningitis and other similar conditions since the symptoms of these diseases are similar but the treatment methods are different. Prolonged course of AmB treatment followed by itraconazole as recommended for T. marneffei non-CNS infection combined with early initial ART might reduce the mortality rate.