2 A 45-year-old man who had been feeling unwell for several months visited his internist complaining of headache, dizziness, nausea, vomiting, extreme tiredness, and fever. The patient had been taking prednisone for a relapse of chronic ulcerative colitis.
3 On examination, the physician noted that the patient had nuchal rigidity and appeared confused. He performed a lumbar puncture. CSF was sent to the laboratory for bacterial and viral cultures. The Gram stain showed many neutrophils but no bacteria.
4 To rule out amebic encephalitis, the physician asked that a wet mount be prepared from the patient’s CSF. Microscopic examination of this preparation revealed motile amebic trophozoites. Cultures were negative for bacteria and viruses.
5 A biopsy specimen containing the parasite causing this patient’s infection is shown in Fig. 29.1.
7 QUESTIONS1. Which ameba would you expect to be causing this patient’s infection? What is the name of this infection?
8 Answer Acanthamoeba spp. granulomatous amebic encephalitis (GAE) Once infected, a person may suffer with headaches, stiff neck, nausea and vomiting, tiredness, confusion, lack of attention to people and surroundings, loss of balance and bodily control, seizures, and hallucinations. Signs and symptoms progresses over several weeks and death usually occurs.
9 QUESTIONS2. Which ameba may cause a more serious and acute CNS infection and may be confused with this parasite?
10 Answer Naegleria fowleri Infection with Naegleria causes the disease primary amebic meningoencephalitis (PAM), a brain inflammation, which leads to the destruction of brain tissue.Initial signs and symptoms of PAM include headache, fever, nausea, vomiting, and stiff neck. As the ameba causes more extensive destruction of brain tissue this leads to confusion, lack of attention to people and surroundings, loss of balance and bodily control, seizures, hallucinations. The disease progresses rapidly and infection usually results in death within 3 to 7 days.
11 QUESTIONS3. How can you distinguish between these amebae?
16 AnswerPAM occurs in persons who are generally healthy prior to infection. Central nervous system involvement arises from organisms that penetrate the nasal passages and enter the brain through the cribriform plate. The organisms can multiply in the tissues of the central nervous system and may be isolated from spinal fluid. In untreated cases death occurs within 1 week of the onset of symptoms.
17 AnswerGAE occurs in persons who are immunodeficient in some way; the organisms cause a granulomatous encephalitis that leads to death in several weeks to a year after the appearance of symptoms. The primary infection site is thought to be the lungs, and the organisms in the brain are generally associated with blood vessels, suggesting vascular dissemination. Prior to 1985 amoebae had been reported isolated from diseased eyes only rarely; cases were associated with trauma to the eye. In , 24 eye cases were reported to CDC and most of these occurred in wearers of contact lenses. It has been demonstrated that many of these infections resulted from the use of home-made saline solutions with the contact lenses.
18 QUESTIONS5. How is the laboratory diagnosis of this infection made?
19 AnswerIn Naegleria infections, the diagnosis can be made by microscopic examination of cerebrospinal fluid (CSF). A wet mount may detect motile trophozoites, and a Giemsa-stained smear will show trophozoites with typical morphology.
20 AnswerIn Acanthamoeba infections, the diagnosis can be made from microscopic examination of stained smears of biopsy specimens (brain tissue, skin, cornea) or of corneal scrapings, which may detect trophozoites and cysts. Cultivation of the causal organism, and its identification by direct immunofluorescent antibody, may also prove useful.
21 QUESTIONS6. Does the ameba causing CNS infection in this patient cause other types of infections?
22 AnswerAcanthamoeba can enter the skin through a cut, wound, or through the nostrils. Once inside the body, amebas can travel to the lungs and through the bloodstream to other parts of the body, especially the central nervous system (brain and spinal cord).
23 AnswerThrough improper storage, handling, and disinfection of contact lenses, Acanthamoeba can enter the eye and cause keratitis resulting superficial corneal abrasions.
24 QUESTIONS7. Which other free-living ameba, recently placed in the same genus as this parasite, causes a CNS infection in humans?
26 QUESTIONS8. Why is there no satisfactory treatment available to treat this infection?
27 AnswerTreatment with sulfamethazine may be effective in controling Acanthamoeba spp.The following agents have been used to successfully eliminate the amoebic infection in the eye: ketoconazole, microconazole, and propamidine isothionate; however, penetrating keratoplasty has been necessary to restore useful vision.