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Acanthamoeba incidence increases
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Despite awareness from both clinicians and patients and better instructions on how to care for contact lenses, the incidence of Acanthamoeba keratitis infections appears to be on the rise, according to clinical studies.
Two clinicians spoke to Primary Care Optometry News about how to prevent, detect and treat such infections.
Infections on the rise
Studies have shown that the incidence of Acanthamoeba keratitis (AK) infections is increasing.
 A dendriform lesion appears in the peripheral cornea of an AK patient. Image: Driebe W |
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“No cohort studies have been performed, which, from an epidemiologic standpoint, is necessary to estimate the true incidence rate,” Charlotte E. Joslin, OD, FAAO, assistant professor at the University of Illinois at Chicago (UIC), Department of Ophthalmology and Visual Sciences and a PhD candidate in epidemiology at the UIC School of Public Health, told PCON in an interview. “However, in 2006 we demonstrated nearly a sevenfold increase in Chicago AK cases beginning in 2003 compared to the early part of the decade, and the CDC [Centers for Disease Control and Prevention] similarly found a nationwide increase beginning in 2004.
“Historical estimates,” she continued, “which probably had more complete nationwide case ascertainment than recent studies, conservatively estimated incidence rates of one to two cases per 1 million contact lens users during the AK outbreaks of the 1980s.”
Majority of cases in contact lens wearers
Dr. Joslin said upwards of 90% of AK infections are in contact lens wearers.
“No brand or type of contact lens is immune to the infection,” PCON Editorial Board member Joseph P. Shovlin, OD, FAAO, said in an interview. “For example, many years ago we were using a lot of tap water or well water rinses in gas-permeable lens wearers. A handful of GP lens wearers in our practice would get Acanthamoeba.”
“Since we’ve deviated from what was once the dogma of using a well water or tap water rinse,” he continued, “a number of GP lens infections have dramatically decreased, but there certainly has been an uptick or insurgence in AK in soft lens wearers in the past several years.”
Signs, symptoms of AK
Acanthamoeba initially causes multiple surface changes.
“It typically will show a patchy involvement where you can have a dendriform pattern or some other form of irregularity or even a pleomorphic epitheliopathy, even with an intact epithelium,” Dr. Shovlin said. “Any time there’s a persistent defect that’s not healing appropriately, I’d be concerned about Acanthamoeba.”
A raised branching pattern that looks like herpes simplex also may emerge, he said. “Herpes simplex virus is an ulcerative or excavated branching dendriform,” Dr. Shovlin continued. “The other lesions that are part of the differential of branching lesions are elevated. Unfortunately, still today, a lot of these infections are confused for herpes simplex,” he said.
Clinicians also should look for a white spot that looks like a bull’s-eye lesion in the epithelium. The stroma can show significant changes and have a granulomatous inflammation, Dr. Shovlin said. “The key to stromal findings would be a lightning flash appearance, radial nerve infiltrates or what we call (radial) keratoneuritis,” he said. “That is almost pathognomonic for AK, but can also be found in leprosy and an unusual nonulcerative form of Pseudomonas.”
“The last thing from the stromal perspective would be a ring infiltrate,” he continued. “Ring infiltrates are not pathognomonic for AK, but certainly would be highly suggestive in the right risk group. This finding generally appears later. You can get nonspecific findings such as hyphema, hypopyon and scleritis. These patients have significant inflammation. They could even have an adenopathy.”
Another problem with AK that often may cloud a clinical picture is the presence of a co-infection.
“You may culture bacteria and amoeba from the same cornea. That’s pretty devastating,” Dr. Shovlin said. “Sadly, many of these folks have poor outcomes – 20% may require transplants. We had one patient who had an enucleation.”
Nonresponse to treatment cause for concern
Clinicians should suspect AK infection if a patient has a nonspecific keratitis that does not respond well to seemingly appropriate therapy, Dr. Shovlin advised.
“If a patient seems to have a contact lens related inflammation and you treat that inflammation with appropriate medication, and the patient doesn’t significantly improve within a few days, I would be quite concerned that there may be something a little more sinister occurring.”
Confirming the diagnosis
Treatment or eradication of the disease can be easier if the condition is diagnosed before a foothold is made into the stroma, Dr. Shovlin said.
“With deeper involvement into the cornea, a corneal biopsy may be necessary to make a diagnosis,” he said. “If you are fortunate enough to have confocal microscopy, that’s a valuable tool, because you can not only make an initial diagnosis, but you can use it to follow the patient and ensure that your treatment plan is working.”
Because so few practices outside of tertiary care centers have access to confocal microscopy, a diagnosis may have to be based on “clinical suspicion, corneal scraping or superficial keratectomy/biopsy,” Dr. Shovlin said.
Cultures are frequently not performed as a result of the high frequency of false negatives, Dr. Joslin said.
“The confocal microscope in the hands of an experienced operator can be useful in early diagnosis, as can superficial corneal scrapings,” she said.
Resurgence of infections
“There were some cases of persistent keratitis that were grafted in the past that did not, even after close inspection, show any cause. Back in the 1980s a heightened awareness for this disease may have accounted for an increased reporting. It is doubtful that this is a factor at all today,” Dr. Shovlin said.
“I’m not convinced there’s a total environmental shift, but certain areas have experienced natural disasters,” he continued. “For example, our area experienced massive flooding about 4 years ago, and we definitely saw an increase in the number of cases in northeast Pennsylvania around that time.”
In fact, doctors in the referral center where Dr. Shovlin works have reported eight AK cases in the past 2 years, a number he calls “significant” considering “we were probably lucky to have just eight cases in the last 25 years before.”
Dr. Joslin studies environmental risk factors in the Chicago area, such as whether the domestic water supply may be contributory to disease.
Getting back to the basics
There has been hot debate about how well multipurpose solutions perform against rare nonbacterial infections. Because of this, experts agree that clinicians should tell patients to rub and rinse their lenses, no matter what the label advises.
“Acanthamoeba cysts and trophozoitesdon’t adhere tenaciously to a lens like Pseudomonas does,” Dr. Shovlin said.
Treatment
Patients should be started on topical polyhexamethylene biguanide 0.02% (PHMB) around the clock for 2 days every hour, alternating on the half hour with propamidine isethionate 0.1%, Dr. Shovlin suggested. Chlorhexidine digluconate 0.02% also can be used instead of the biocide listed above, Dr. Shovlin said.
There also are two popular antiparasitics that are not readily available.
Monotherapy with one of the biocides such as chlorhexidine or a biguanide such as Baquacil (PHMB, Zeneca) could be attempted. “However, initially we use Brolene (propamidine isethionate 0.1%) in addition to Baquacil.
“Antineoplastic and antimalarial medications may have a role in the management of this disease, but need to undergo further study,” he said.
For more information:
- Joseph P. Shovlin, OD, FAAO, is a Primary Care Optometry News Editorial Board member who practices at Northeastern Eye Institute in Scranton, Pa. He can be reached at 200 Mifflin Ave., Scranton, PA 18503; (570) 342-3145; fax: (570) 344-1309; e-mail: jpshovlin@gmail.com.
- Charlotte E. Joslin, OD, FAAO, is an assistant professor at the University of Illinois at Chicago, Department of Ophthalmology and Visual Sciences and a PhD candidate in epidemiology at the UIC School of Public Health. She can be reached at 1855 W. Taylor St., Ste. 3.164, Chicago, IL 60612; (312) 996-5410; fax: (312) 996-4255; e-mail: charjosl@uic.edu.
References:
- Acanthamoeba keratitis multiple states, 2005-2007. Morb Mortal Wkly Rep. 2007;56(21):532-534.
- Joslin CE, Tu EY, McMahon TT, et al. Epidemiological characteristics of a Chicago-area Acanthamoeba keratitis outbreak. Am J Ophthalmol. 2006;142(2):212-217 e212.
- Joslin CE, Tu EY, Shoff ME, et al. The association of contact lens solution use and Acanthamoeba keratitis. Am J Ophthalmol. 2007;144(2):169-180.
- Schaumberg DA, Snow KK, Dana MR. The epidemic of Acanthamoeba keratitis: where do we stand? Cornea. Jan 1998;17(1):3-10.
- Tu EY, Joslin CE, Sugar J, et al. The relative value of confocal microscopy and superficial corneal scrapings in the diagnosis of Acanthamoeba keratitis. Cornea. 2008;27(7):764-772.