Vol

DEPARTMENT OF PATHOLOGY The Johns Hopkins Medical Institutions
Vol. 18, No. 3
THE JOHNS HOPKINS MICROBIOLOGY NEWSLETTER
Tuesday, January 19, 1999

Provided by Leslie Edwards Reger, Division of Outbreak Investigation, Maryland Department of Health and Mental Hygiene.

6 outbreaks reported from 1/4/99 - 1/8/99: 4 gastroenteritis outbreaks at nursing homes

1 foodborne gastroenteritis associated with a food-service facility, and 1 pneumonia at a nursing home

The Johns Hopkins Hospital. Information provided by Dr. Michael Dardik, Department of Pathology.

Clinical History: A 48 year old male who uses extended wear soft contact lenses was struck in his right eye with the fingernail of his four month old daughter who had an upper respiratory tract infection. He was initially treated at an outside hospital with erythromycin for corneal abrasion. He subsequently developed pain, photophobia, ptosis and decreased vision in the right eye and presented to The Wilmer Institute approximately four weeks after the initial injury. Slitlamp examination revealed a 3.0 x 1.5 mm central corneal ulceration overlying a 3.0 x 2.0 mm active infiltrate. Deep stroma, Descemet’s membrane and the endothelium were unremarkable. Corneal scrapings were negative for bacteria and fungal growth, and the patient was treated with topical steroids and acyclovir. Nonetheless, after four weeks there was no subjective improvement and repeat physical examination was largely unchanged except the stromal infiltrate had a ring-like character. Corneal scrapings were cultured on E. coli supplemented non-nutrient agar and after one day grew Acanthamoeba. The patient was immediately started on polyhexamethylene biguanide, hexamidine and itraconazole.

Acanthamoeba

Acanthamoeba species are free-living protozoa that occupy soil, water, sewage and other microenvironments where in their trophozoite form, they feed on bacteria and yeast. In adverse situations, the Acanthamoeba encyst, and in cyst form are resistant to disinfectants, temperature variation, and desiccation.

Acanthamoeba are responsible for two different clinical diseases, granulomatous amebic meningoencephalitis (GAE) and Acanthamoeba keratitis. GAE is an opportunistic infection of debilitated or chronically ill patients that is characterized by a granulomatous response which is unfortunately rarely diagnosed pre-mortem. In AIDS patients, GAE can have extracranial manifestations.

Acanthamoeba keratitis

Epidemiology: An association between Acanthamoeba keratitis and the wearing of contact lenses has been established. In particular, approximately 85% of infections occur in contact lens wearers, many of who use homemade saline or other contaminated solutions to store and clean lenses. Acanthamoeba keratitis is associated with all styles of contact lenses, including soft, rigid gas-permeable and hybrid lenses. Acanthamoeba keratitis is most common in young adults.

Clinical Features: Most cases of Acanthamoeba keratitis have a history of minor trauma to the eye, which may explain the finding that the majority of cases are unilateral (especially in view of the aforementioned epidemiologic risk factor). Signs and symptoms include ocular pain, photophobia, decreased visual acuity, conjunctival hyperemia, blephorospasm, corneal ulceration, radial keratoneuritis and stromal infiltrates. Although the infiltrates do not always have a ring form, when present, the ring infiltrates are almost pathognomonic for the organism. Similarly, while radial keratoneuritis is highly suggestive of the organism, it is not commonly identified. If the corneal ulceration is untreated, the ulcer may perforate, and if infection spreads to the sclera, enucleation may be necessary.

Diagnosis: Diagnosis is typically delayed, with most cases first being treated for bacterial, fungal, or herpes simplex viral keratitis. Definitive diagnosis can almost always be made from either wet mounts or culture of corneal scrapings without the need to resort to corneal biopsy. Trophozoites and cysts can be identified in smears stained with Giemsa, silver-methenamine and periodic acid-Schiff stains, whereas fluorescent stains (e.g. calcofluor white) are useful but not necessary. Cultures can be inoculated on non-nutrient agar overlaid with E. coli. After a variable number of days, the trophozoites and their paths can be seen with a dissecting microscope, and several days later, as the food supply is exhausted, the Acanthamoeba will encyst.

Therapy: Aggressive antiamoebic medical therapy of Acanthamoeba keratitis is the first line of therapy, with the majority of patients being cured of disease and recovering visual acuity. Typical antiamoebic regimens include various combinations of topical imidazoles (e.g. miconazole, clotrimazole), systemic imidazoles (e.g. itraconazole), topical diamidines (e.g. broline), topical antibiotics (e.g. neomycin) and topical antiseptics (e.g. polyhexamethylene biguanide). As there may be a higher failure rate in-patients who use topical corticosteroids, some investigators have recommended discontinuing their use once a diagnosis of Acanthamoeba keratitis is made. Therapeutic keratoplasty is reserved for patients who fail medical therapy. Bacterial superinfection complicating treatment of Acanthamoeba keratitis has been reported and can be devastating, and the use of prophylactic antibacterial drugs throughout the anti-amoebic treatment course has been advocated.

References

D’Aversa G, Stern GA, Driebe WT Jr. Diagnosis and successful medical treatment of Acanthamoeba keratitis. Archives of Ophthalmology. 113(9): 1120-3, 1995 Sep.
Morlet N, Duguid G, Radford C, Matheson M, Dart J. Incidence of Acanthamoeba keratitis associated with contact lens wear. The Lancet. 350 (9075): 414-6, 1997 Aug.
Walker CW. Acanthamoeba: ecology, pathogenicity and laboratory detection. British Journal of Biomedical Science. 53 (2): 146-51, 1996 Jun.