Current Status of Acanthamoeba in Iran: A Narrative Review Article

Background:

Free-living amoebae belonging to the genus Acanthamoeba have an environmental distribution. Amoebic keratitis due to these protozoan parasites continue to rise in Iran and worldwide. In Iran, there are various researches regarding both morphological and molecular identification of Acanthamoeba spp. in environmental and clinical samples. However, there is no thorough review about Acanthamoeba genotypes and their distribution in environmental sources such as water, dust and biofilm in Iran. Besides, according to increasing cases of Amoebic keratitis in the region awareness regarding the pathogenic potential of these sight-threatening amoebae is of utmost importance.

Methods:

We conducted a thorough review based on the database sources such as MEDLINE, PubMed and Google scholar. No restrictions were placed on study date, study design or language of publication. We searched all valuable and relevant information considering the occurrence of the Acanthamoeba in both environmental and clinical samples.

Results:

According to our thorough review Acanthamoeba belonging to T4 genotype is the most prevalent type strain in environmental and clinical samples in several regions in Iran and worldwide, however, there are reports regarding Acanthamoeba belonging to other genotypes such as T2, T3, T5, T6 and T11 and the mentioned point could leads us to more researches with the goal of presenting the real genotype dominance of Acanthamoeba and related disease in the country.

Conclusion:

Overall, the present review will focus on present status of genotypes of Acanthamoeba in Iran during recent years.     

Coexistent adenoviral keratoconjunctivitis and Acanthamoeba keratitis

A 17-year-old youth presented with bilateral follicular conjunctivitis and nummular subepithelial corneal infiltrates. Failure of this to settle in an outpatient setting led to corneal scraping with microscopy and culturing for bacteria, fungi, Herpes simplex, adenovirus and Acanthamoeba as an inpatient. Polymerase chain reaction analysis of corneal cells was positive for adenovirus, and culture on live Escherichia coli-coated agar plates was positive for Acanthamoeba by phase contrast microscopy on day two. We conclude that Acanthomoeba infection can complicate adenoviral keratoconjunctivitis. This observation is in keeping with previously reported modes of infection by Acanthamoeba, whereby any epithelial breach seems to allow inoculation of the eye by this opportunistic organism.     

Infectious keratitis in orthokeratology

Orthokeratology is a method of changing refraction in myopic patients by using rigid contact lenses to reduce the curvature of the cornea. This treatment was in use in the two cases of corneal ulcer described in this paper and appears to have contributed to the development of their disease. As with extended wear contact lenses, patients undergoing orthokeratology treatment are frequently advised to wear the orthokeratology lenses overnight increasing the risk of corneal ulceration and infection. Patients should be adequately warned of the associated risks and advised that any envisaged benefits of the procedure are temporary.     

Acanthamoeba keratitis: multicentre survey in England 1992-6

AIM—To investigate the frequency, outcomes, and risk factors for acanthamoeba keratitis (AK) in England during the past 4 years.
METHODS—An ophthalmologist in 12 of the 14 regional health authorities (RHAs) coordinated identification of patients in their region presenting with AK between 1 October 1992 and 30 September 1996. Clinical and postal patient questionnaire data were analysed.
RESULTS—243 patients (259 eyes) with an AK diagnosis were identified, equating to an annualised incidence of 0.14 per 100 000 individuals. UK resident patients for each year numbered 50, 71, 73, and 32 respectively. Among patients with sufficient data 170/237 (72%) were diagnosed early (within 30 days of presentation), 197/218 (90%) were treated with polyhexamethyl biguanide and/or chlorhexidine, and 40/243 (16%) underwent surgery. Visual acuities of 6/12 or better were achieved by 222/259 (86%) eyes, including 84 eyes of patients under review or lost to follow up. Non-contact lens (CL) wearers were associated with delayed diagnosis, increased need for surgery and a poorer visual outcome (only 10/18 eyes, 56%, achieved 6/12 acuity). 225/243 (93%) patients were CL wearers, and 205/243 (84%) were soft CL (SCL) users. Among SCL user respondents, previously identified risk factors—swimming with CL (47/138, 34%), non-sterile CL rinsing (11/138, 8%), omitted disinfection (85/138, 62%), and chlorine release disinfection (65/138, 47%)—were identified for 125/138 (91%) patients.
CONCLUSIONS—Earlier diagnosis and more effective medical therapy have improved the prognosis for most AK patients. The study demonstrates the highly preventable nature of the disease: 91% of the SCL wearers could have avoided the disease by refraining from inadvisable practices, and a marked fall in frequency was seen after intensive media attention to AK, possibly in conjunction with increasing penetrance of new CL products. Since the frequency of AK appears to be largely determined by the ever changing trends in CL use, continued monitoring is indicated.

Keywords: keratitis; Acanthamoeba; multicentre survey; England     

Heidelberg Retina Tomograph II Findings of Acanthamoeba Keratitis

Purpose: Heidelberg retina tomograph II (HRTII) examination was performed with cornea module in one patient with Acanthamoeba keratitis (AK) to provide images detailing characteristic findings of the disease. Methods: A 34-year-old woman presented with clinical signs and symptoms of AK. HRTII with cornea module was performed and the patient underwent laboratory investigations. Results: HRTII examination with cornea module revealed numerous 20–26-μ m diameter high-contrast round particles within the corneal epithelium and anterior stroma, resembling Acanthamoeba cysts. Stellate cells as well as ovoid irregular objects, possibly inflammatory cells, trophozoites, altered cysts, or activated keratocytes, were also present in the area of stromal infiltrates. Laboratory investigations confirmed the diagnosis of AK. Conclusions: HRTII cornea module can be helpful in the diagnosis of AK by identifying acanthamoeba cyst-like structures in the cornea. This technique also has potential uses in monitoring the efficiency of anti-infective treatment.     

Dual Targeting of Function–Structure for Effective Killing of Pathogenic Free-Living Amoebae

Here we discuss the potential value of targeting both the hardy structure of the cyst state of the parasite, in addition to the active trophozoite form, to provide target-directed inhibition as a viable drug strategy in the effective eradication of parasites.     

Corneal biopsy in microbial keratitis

Presumed microbial keratitis in the absence of a specific microbiological diagnosis is a particularly difficult clinical problem. Corneal biopsy may provide the diagnosis when corneal scrapings have been negative. We present two cases in which corneal biopsy was helpful and discuss the role of corneal biopsy in the management of chronic keratitis     

Fatal disseminated Acanthamoeba lenticulata infection in a heart transplant patient

We report a fatal case of disseminated acanthamebiasis caused by Acanthamoeba lenticulata (genotype T5) in a 39-year-old heart transplant recipient. The diagnosis was based on skin histopathologic results and confirmed by isolation of the ameba from involved skin and molecular analysis of a partial 18S rRNA gene sequence (DF3).     

棘阿米巴性角膜炎行角膜移植术的临床观察

目的 回顾性分析13例棘阿米巴性角膜溃疡行角膜移植手术治疗的临床效果.方法 临床诊断棘阿米巴性角膜炎患者13例,其中6例行板层角膜移植术,7例行穿透性角膜移植术,术后继续应用抗阿米巴药物1～3个月.结果 术后随访6个月至2年,感染均得到控制.术后视力情况,LK术后指数的1例,0.02 ～ 0.1的3例,0.12～0.3的2例,PK术后小于0.02的3例,0.02～0.1的2例,0.12～0.3的2例.结论 棘阿米巴性角膜炎在药物不能控制的情况下,行角膜移植术可有效控制炎症,根据病灶的深度合理选择术式,术后可获得良好的治疗效果.同时术后辅以抗阿米巴药物的治疗可以起到辅助治疗的目的.