Free Living Amoebae Lecture PDF - King Salman International University

Faculty of Medicine Level 3 CNS module Lecture : Free living amoebae Prof. Gehan Salah Sadek Date : 15/ 11 /2022 Intended Learning Outcomes By the end of the lecture, the student will be able to: 1) Recognize the mode of transmission of free living amoebae. 2) Differentiate between Nae...

Faculty of Medicine Level 3 CNS module Lecture : Free living amoebae Prof. Gehan Salah Sadek Date : 15/ 11 /2022 Intended Learning Outcomes By the end of the lecture, the student will be able to: 1) Recognize the mode of transmission of free living amoebae. 2) Differentiate between Naegleria fowleri and Acanthamoeba sp. 3) Describe the clinical picture of primary amoebic meningoencephalitis, granulomatous amoebic encephalitis and Acanthamoeba keratitis. 4) Support the preventive measures for infections caused by free living amoebae. Training methods  Free living amoebae Pathogenic free -living amoebae Non-pathogenic free - living amoebae (Coprozoic)  Pathogenic free - living amoebae Acanthamoeba sp. Naegleria fowleri Acanthamoeba Granulomatous Primary amoebic keratitis amoebic encephalitis meningoencephalitis  Naegleria fowleri It is the only ameba with three known morphologic forms: 1) Ameboid trophozoites. 2) Flagellate forms. (pertains to protozoa that move by means of flagella) 3) cysts. Quoted from Clinical Parasitology: A practical approach Epidemiology * N. fowleri is primarily found in warm bodies of water, including lakes, streams, ponds, and swimming pools. *Prevalence is higher in the summer months of the year. Mode of transmission - The ameboid trophozoite of N. fowleri (Infective stage) enters the human body through the nasal mucosa (e.g. during swimming). Clinical picture Asymptomatic: Patients who contract N. fowleri resulting in colonization of the nasal passages are usually asymptomatic. Primary amebic meningoencephalitis (PAM) What do you expect?  Primary amoebic meningoencephalitis (PAM) * Pathology N. fowleri invade the brain, causing rapid tissue destruction. * Initial clinical manifestations: Fever, headache, sore throat, nausea, and vomiting. * Symptoms of meningitis rapidly follow, including stiff neck and seizures. * The patient will often experience smell and taste alterations, blocked nose, and Kernig’s sign. * In untreated patients, death usually occurs 3 to 6 days after onset. * Postmortem brain tissue samples of these patients reveal the typical ameboid trophozoites of N. fowleri. What is meant by Kernig’s sign? A diagnostic sign for meningitis, where the patient is unable to fully straighten his or her leg when the hip is flexed at 90 degrees because of hamstring stiffness Naegleria infection (Brain eating amoebae) Naegleria infection (Brain eating amoebae)  Diagnosis 1) Microscopic examination of cerebrospinal fluid (CSF) is the method of choice for the recovery of N. fowleri ameboid trophozoites: Saline and iodine wet preparations of the CSF are recommended. 2) Samples of nasal discharge may also be examined. Specimens can be cultured to show N. fowleri ameboid trophozoites. Treatment Unfortunately, medications used to treat meningitis and amebic infections are ineffective against N. fowleri. There is evidence, however, that prompt and aggressive treatment with amphotericin B may be of benefit to patients suffering from infections with N. fowleri, despite its known toxicity. In rare cases, amphotericin B in combination with rifampin or miconazole has also proved to be an effective treatment. A person can survive if signs are recognized early but, if not, PAM almost always results in death. Prevention and Control Health Education Adequate chlorination of the swimming pools and hot tubs Immediate repairing of cracks found in the walls of pools, hot tubs, and baths to prevent a possible source of contamination  Acanthamoeba species Common associated disease or condition names: Granulomatous amebic encephalitis (GAE), Acanthamoeba keratitis Acanthamoeba sp. trophozoite Quoted from Clinical Parasitology: A practical approach Acanthamoeba sp. cyst Quoted from Clinical Parasitology: A practical approach Mode of transmission 1) Aspiration or nasal inhalation of the organisms. Trophozoites and cysts enter via the lower respiratory tract. These organisms often migrate via hematogenous spread and invade the central nervous system (CNS), causing serious CNS infections. 2) Direct invasion of the parasite in the eye. Two groups of individuals are at risk for direct eye invasion: a) Contact lens wearers b) Those who have experienced trauma to the cornea. (Eye infection will be taught in the special senses module). Clinical picture Predisposing factor: CNS infections primarily occur in patients who are immunocompromised or debilitated. 1) Symptoms of this condition develop slowly over time and include headaches, seizures, stiff neck, nausea, and vomiting. Granulomatous lesions of the brain are characteristic and may contain both Acanthamoeba trophozoites and cysts. 2) Sometimes, Acanthamoeba spp. invade other areas of the body, including the kidneys, pancreas, prostate, and uterus, and form similar granulomatous lesions. Diagnosis The specimen of choice is CSF (Examination is done as in Naegleria). Treatment Because of the slow progression of GAE, most patients who suffer from it die, not only before an accurate diagnosis may be made, but also before experimental treatments can be administered and studied. There is some evidence to suggest that sulfamethazine might be a suitable treatment.