An unusual case of fungal keratitis: Metarrhizium anisopliae

The Spectrum of Microbial Keratitis: An Updated Review

Background:

In microbial keratitis, infection of the cornea can threaten vision through permanent corneal scarring and even perforation resulting in the loss of the eye. A literature review was conducted by Karsten, Watson and Foster (2012) to determine the spectrum of microbial keratitis. Since this publication, there have been over 2600 articles published investigating the causative pathogens of microbial keratitis.

Objective:

To determine the current spectrum of possible pathogens implicated in microbial keratitis relative to the 2012 study.

Methods:

An exhaustive literature review was conducted of all the peer-reviewed articles reporting on microbial pathogens implicated in keratitis. Databases including MEDLINE, EMBASE, Scopus and Web of Science were searched utilising their entire year limits (1950-2019).

Results:

Six-hundred and eighty-eight species representing 271 genera from 145 families were implicated in microbial keratitis. Fungal pathogens, though less frequent than bacteria, demonstrated the greatest diversity with 393 species from 169 genera that were found to cause microbial keratitis. There were 254 species of bacteria from 82 genera, 27 species of amoeba from 11 genera, and 14 species of virus from 9 genera, which were also identified as pathogens of microbial keratitis.

Conclusion:

The spectrum of pathogens implicated in microbial keratitis is extremely diverse. Bacteria were most commonly encountered and in comparison, to the review published in 2012, further 456 pathogens have been identified as causative pathogens of microbial keratitis. Therefore, the current review provides an important update on the potential spectrum of microbes, to assist clinicians in the diagnosis and treatment of microbial keratitis.

Two cases of fungal keratitis caused by Metarhizium anisopliae

We present two cases of keratitis due to Metarhizium anisopliae in geographically separated areas of the United States. The isolates were microscopically similar but morphologically different and were identified by ribosomal DNA sequencing. Both isolates had low minimum inhibitory concentration (MIC) values to caspofungin and micafungin, but high MIC values to amphotericin B. The morphologic and antifungal susceptibility differences between the two isolates indicate possible polyphylogeny of the group.

Species of the Metarhizium anisopliae complex with diverse ecological niches display different susceptibilities to antifungal agents

Species of the Metarhizium anisopliae complex are globally ubiquitous soil-inhabiting and predominantly insect-pathogenic fungi. The Metarhizium genus contains species ranging from specialists, such as Metarhizium acridum that only infects acridids, to generalists, such as M. anisopliae, Metarhizium brunneum, and Metarhizium robertsii that infect a broad range of insects and can also colonize plant roots. There is little information available about the susceptibility of Metarhizium species to clinical and non-clinical antifungal agents. We determined the susceptibility of 16 isolates comprising four Metarhizium species with different ecological niches to seven clinical (amphotericin B, ciclopirox olamine, fluconazole, griseofulvin, itraconazole, tebinafine, and voriconazole) and one non-clinical (benomyl) antifungal agents. All isolates of the specialist M. acridum were clearly more susceptible to most antifungals than the isolates of the generalists M. anisopliae sensu lato, M. brunneum, and M. robertsii. All isolates of M. anisopliae, M. brunneum, and M. robertsii were resistant to fluconazole and some were also resistant to amphotericin B. The marked differences in susceptibility between the specialist M. acridum and the generalist Metarhizium species suggest that this characteristic is associated with their different ecological niches, and may assist in devising rational antifungal treatments for the rare cases of mycoses caused by Metarhizium species.

Surgical treatment of Metarhizium anisopliae sclerokeratitis and endophthalmitis

A 55-year-old nurse was referred with a 5-month history of right eye corneal abscess. The initial injury occurred when doing lawn work. The infection worsened despite multiple antibiotic, antiviral, and steroid treatments. Visual acuity was limited to hand motion. On examination, there was keratitis, ocular hypertension, and a secondary cataract. Corneal scrapings grew a filamentous fungus, identified as Metarhizium anisopliae (MA). Despite intensive antifungal treatment with topical, intravitreous, and systemic voriconazole, purulent corneal melting and scleritis with endophthalmitis rapidly appeared. An emergency surgical procedure including sclerocorneal transplantation, cataract surgery, a pars plana vitrectomy using temporary keratoprosthesis, and scleral crosslinking was necessary. One year after the surgery, there was no recurrence of infection. Functional outcome remained very poor. This is the first case of sclerokeratitis and endophthalmitis caused by MA ever reported. The infection was successfully treated with an aggressive combination of medical and surgical treatments.

Fungal keratitis caused by Metarhizium anisopliae complex

Purpose

To report a case of fungal keratitis caused by Metarhizium anisopliae complex

Methods

Case report

Results

Our patient presented with a central corneal infiltrate. Fungal culture yielded a Metarhizium species. She was started on antifungal agents with no significant improvement. A therapeutic corneal transplant was performed after perforation. At two years follow up, she was free of infection.

Conclusion

Metarhizium anisopliae is a very rare cause of keratitis. Although previous reported cases showed clinical improvement with antifungal agents, this case required surgical treatment to control the infection.

Species of Metarhizium anisopliae complex implicated in human infections: retrospective sequencing study

OBJECTIVES

Fungi belonging to the Metarhizium anisopliae complex comprise ubiquitous arthropod pathogenic moulds used as mycopesticides. Rare cases of human infections due to M. anisopliae have been reported. We hypothesize misidentifications of fungal strains implicated in these cases or used in mycopesticides.

METHODS

A review of the literature was conducted to identify previously published cases. We collected some of these previous described strains and reported new cases, and a French mycopesticide containing M. anisopliae. All identifications were performed based on elongation factor-1α gene sequencing.

RESULTS

We report eight new cases of Metarhizium infection in humans (three from France and five from Australia). The strains isolated from these cases, and three others from already published cases and reported as M. anisopliae, were molecularly identified based on elongation factor-1α (Ef1-α) gene sequencing as follows: Metarhizium robertsii (six), Metarhizium guizhouense (three), Metarhizium brunneum (one) and Metarhizium pingshaense (one).

CONCLUSIONS

In this study, we report new human cases of Metarhizium infections, and, based on Ef-1α gene sequencing, we demonstrate the misidentification of species in case reports. We also correct the species identification of a strain reported as M. anisopliae used in a commercially available mycopesticide. According to our results, none of the strains from the human infection reports reviewed belongs to the species M. anisopliae.

First unusual case of keratitis in Europe due to the rare fungus Metarhizium anisopliae

Metarhizium anisopliae is a fungus utilized worldwide for insect-pest biocontrol. Few M. anisopliae infections have been reported previously. Here, M. anisopliae was isolated from a corneal ulcer in a healthy man. It is the first ocular case in France and Europe of this extremely rare fungus in humans.

Severe fungal sclerokeratitis caused by Metarhizium anisopliae: a case report and literature review

To date, there has been only one published report on the infectious sclerokeratitis caused by Metarhizium anisopliae, which is an entomopathogenic fungus. Regarding corneal infection, three reports have been published to date. Although the prognoses of the corneal infections are favourable, prognosis when scleral infection is involved is very poor. A 76-year-old patient presented with foreign body sensation in the left eye. Microscopic examination with Fungi Flora Y staining of the corneal scraping revealed fungal infection. The conjunctiva was melted by the infection over a wide area. Although intensive medications were administered, an emergency surgery was necessary because scleral thinning, corneal perforation and lens prolapse occurred. The fungal isolate was identified as M. anisopliae by sequencing the internal transcribed spacer region. Herein, we report the second known case worldwide of M. anisopliae sclerokeratitis, and we review the literature related to the ocular infections.

Keratitis due to the wood saprobic ascomycete, Auerswaldia lignicola (Family Botryosphaeriaceae), in a carpenter in India

Keratitis due to Auerswaldia lignicola in a 32-year-old Indian male carpenter is described. At presentation, the patient reported persistent pain and tearing (left eye) in spite of topical antimicrobial therapy for more than 3 weeks. Clinically, mycotic keratitis was suspected, and direct microscopy of corneal scrapings stained by lactophenol cotton blue and Gram stains revealed broad septate hyphae. Intensive topical antifungal therapy was then given for 15 days. The keratitis continued to progress, necessitating therapeutic penetrating keratoplasty. Following the keratoplasty, there was rapid reduction in inflammation and gradual quietening of the eye. Brown-black fungal colonies resembling Lasiodiplodia theobromae were isolated from corneal scrape and corneal button (post-surgery) material on Sabouraud glucose-neopeptone agar; however, sporulation did not occur, so the morphological identification could not be confirmed. Sequence analysis of the 18S rRNA region of extracted fungal genomic DNA yielded an identification of A. lignicola Ariyawansa, J.K. Liu & K.D. Hyde; the sequence data have been deposited in GenBank (A. lignicola strain DK/V4, accession number KC866317.1). Medical management of keratitis due to such rarely reported fungal species may be difficult, necessitating surgical procedures.

Computed tomography of granulomatous pneumonia with oxalosis in an American alligator (Alligator mississippiensis) associated with Metarhizium anisopliae var anisopliae

An 18-yr-old, male, albino, American alligator (Alligator mississippiensis) was evaluated for decreased appetite and abnormal buoyancy. Computed tomography (CT) of the coelomic cavity showed multifocal mineral and soft tissue attenuating pulmonary masses consistent with pulmonary fungal granulomas. Additionally, multifocal areas of generalized, severe emphysema and pulmonary and pleural thickening were identified. The alligator was euthanized and necropsy revealed severe fungal pneumonia associated with oxalosis. Metarhizium anisopliae var. anisopliae was cultured from lung tissue and exhibited oxalate crystal formation in vitro. Crystals were identified as calcium oxalate monohydrate by X-ray powder defractometry. Fungal identification was based on morphology, including tissue sporulation, and DNA sequence analysis. This organism is typically thought of as an entomopathogen. Clinical signs of fungal pneumonia in nonavian reptiles are often inapparent until the disease is at an advanced stage, making antemortem diagnosis challenging. This case demonstrates the value of CT for pulmonary assessment and diagnosis of fungal pneumonia in the American alligator. Fungal infection with associated oxalosis should not be presumed to be aspergillosis.

Pediatric Metarrhizium anisopliae keratitis

Metarrhizium anisopliae (M. anisopliae) is an entomopathogenic fungus used as an agricultural pesticide in many countries, including the United States. M. anisopliae grows optimally at 25°C and is therefore considered safe to humans. We report a case of a 12-year-old girl who is a soft contact lens wearer with M. anisopliae corneal ulcer who was treated effectively with topical natamycin after identification of the organism by corneal culture. Topical amphotericin B was not effective.

The effects of the fungus Metarhizium anisopliae var. acridum on different stages of Lutzomyia longipalpis (Diptera: Psychodidae)

The control of Visceral Leishmaniasis (VL) vector is often based on the application of chemical residual insecticide. However, this strategy has not been effective. The continuing search for an appropriate vector control may include the use of biological control. This study evaluates the effects of the fungus Metarhizium anisopliae var. acridum on Lutzomyia longipalpis. Five concentrations of the fungus were utilized, 1 x 10(4) to 1 x 10(8) conidia/ml, accompanied by controls. The unhatched eggs, larvae and dead adults previously exposed to fungi were sown to reisolate the fungi and analysis of parameters of growth. The fungus was subsequently identified by PCR and DNA sequencing. M. anisopliae var. acridum reduced egg hatching by 40%. The mortality of infected larvae was significant. The longevity of infected adults was lower than that of negative controls. The effects of fungal infection on the hatching of eggs laid by infected females were also significant. With respect to fungal growth parameters post-infection, only vegetative growth was not significantly higher than that of the fungi before infection. The revalidation of the identification of the reisolated fungus was confirmed post-passage only from adult insects. In terms of larvae mortality and the fecundity of infected females, the results were significant, proving that the main vector species of VL is susceptible to infection by this entomopathogenic fungus in the adult stage.

Atypical fungal sclerokeratitis

PURPOSE

To report a case of fungal sclerokeratitis caused by Metarrhizium anisopliae, which to our knowledge is the first reported case worldwide.

METHODS

A 52-year-old woman presented from rural Australia with a 1-week history of ocular injection involving the right eye without associated pain. Her best-corrected visual acuity was 6/9 in the right eye and 6/6 in the left eye. Intraocular pressure was 40 and 15 mm Hg in the right eye and left eye, respectively. On examination, a 7.0 x 4.5-mm area of corneal infiltrate and adjacent scleral necrosis involving the nasal limbus was evident. Cultures of corneal scrapings grew a filamentous fungus, identified as Metarrhizium anisopliae. The patient was started on multiple antifungal agents including topical natamycin, systemic and topical voriconazole, and eventually systemic and topical posaconazole.

RESULTS

No significant response to antifungal agents over the course of a 25-day hospital admission was seen. A limbus-to-limbus therapeutic corneal graft was performed on eventual perforation. The patient developed multiple postoperative complications including cataract, hypotony, and a flat anterior chamber. Six months after initial presentation, her resulting visual acuity was hand motion, with evidence of early graft failure and hypotony; however, she was free of infection.

CONCLUSIONS

Metarrhizium anisopliae is an extremely rare cause of ocular infection, and this report represents the first case of sclerokeratitis caused by this pathogen worldwide. Although found to be clinically sensitive to antifungal agents in previously reported cases of keratomycosis alone, it was found to be resistant to multiple antifungal agents with devastating consequences with the presence of scleral involvement.

Recurrent disseminated skin lesions due to Metarrhizium anisopliae in an adult patient with acute myelogenous leukemia

Metarrhizium anisopliae is a common insect pathogen that rarely causes infection in animals and humans. We report the first case of a disseminated skin infection in an immunocompromised adult patient. To date, only five cases of the disease in humans have been reported. There is no standard treatment for this infection.