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Live cycle of Acanthamoeba. In the water the cyst becomes a trophozoite. This then undergoies mitosis to form more trophozoites. Trophozoites can also become cysts. The amebae (cysts and trophozoites) can enter humans in various ways. Amoebae can enter through the eye, resulting in severe keratitis of the eye. Whn amoebae enter through nasal passages and infect the lower respiratory tract, it can result in granulomatous amebic encephalitis (GAE) and/or disseminated disease in individuals with compromised immune systems. Amoebae entering through ulcerated or broken skin can cause granulomatous amebic encephalitis (GAE), disseminated disease, or skin lesions in individuals with compromised immune systems.
Acanthamoeba spp. are waterborne parasites very common in unchlorinated aqueous environments. As shown in this life cycle, Acanthamoeba cysts and trophozoites are both capable of entering the body through various routes, causing infections of the eye, skin, and central nervous system. (credit: modification of work by Centers for Disease Control and Prevention)
a) an acanthamoeba cyst is shown. b) an acanthamoeba trophozoite micrograph is shown. c) a photo of an eye with a fluorescent cornea is shown.
(a) An Acanthamoeba cyst. (b) An Acanthamoeba trophozoite (c) The eye of a patient with Acanthamoeba keratitis. The fluorescent color, which is due to sodium fluorescein application, highlights significant damage to the cornea and vascularization of the surrounding conjunctiva. (credit a: modification of work by Centers for Disease Control and Prevention; credit b, c: modification of work by Jacob Lorenzo-Morales, Naveed A Kahn and Julia Walochnik)
  • How are Acanthamoeba infections acquired?

Loiasis

The helminth Loa loa , also known as the African eye worm, is a nematode that can cause loiasis , a disease endemic to West and Central Africa ( [link] ). The disease does not occur outside that region except when carried by travelers. There is evidence that individual genetic differences affect susceptibility to developing loiasis after infection by the Loa loa worm. Even in areas in which Loa loa worms are common, the disease is generally found in less than 30% of the population. Garcia, A.. et al. “Genetic Epidemiology of Host Predisposition Microfilaraemia in Human Loiasis.” Tropical Medicine and International Health 4 (1999) 8:565–74. http://www.ncbi.nlm.nih.gov/pubmed/10499080. Accessed Sept 14, 2016. It has been suggested that travelers who spend time in the region may be somewhat more susceptible to developing symptoms than the native population, and the presentation of infection may differ. Spinello, A., et al. “Imported Loa loa Filariasis: Three Cases and a Review of Cases Reported in Non-Endemic Countries in the Past 25 Years.” International Journal of Infectious Disease 16 (2012) 9: e649–e662. DOI: http://dx.doi.org/10.1016/j.ijid.2012.05.1023.

The parasite is spread by deerflies (genus Chrysops ), which can ingest the larvae from an infected human via a blood meal ( [link] ). When the deerfly bites other humans, it deposits the larvae into their bloodstreams. After about five months in the human body, some larvae develop into adult worms, which can grow to several centimeters in length and live for years in the subcutaneous tissue of the host.

The name “eye worm” alludes to the visible migration of worms across the conjunctiva of the eye. Adult worms live in the subcutaneous tissues and can travel at about 1 cm per hour. They can often be observed when migrating through the eye, and sometimes under the skin; in fact, this is generally how the disease is diagnosed. It is also possible to test for antibodies, but the presence of antibodies does not necessarily indicate a current infection; it only means that the individual was exposed at some time. Some patients are asymptomatic, but in others the migrating worms can cause fever and areas of allergic inflammation known as Calabar swellings . Worms migrating through the conjunctiva can cause temporary eye pain and itching, but generally there is no lasting damage to the eye. Some patients experience a range of other symptoms, such as widespread itching, hives, and joint and muscle pain.

Worms can be surgically removed from the eye or the skin, but this treatment only relieves discomfort; it does not cure the infection, which involves many worms. The preferred treatment is diethylcarbamazine , but this medication produces severe side effects in some individuals, such as brain inflammation and possible death in patients with heavy infections. Albendazole is also sometimes used if diethylcarbamazine is not appropriate or not successful. If left untreated for many years, loiasis can damage the kidneys, heart, and lungs, though these symptoms are rare.

The first part of the image is a photograph of an eye with a visible worm inside of it and a photo of a close-up of the worm. The second image is a illustrated chart showing the Life cycle of Lao lao. Fly (genus Chrysops) takes a blood meal (L3 larvae enter the bite wound). Adults grow into long worms in the subcutaneous tissue. Adults produce sheathed microfilariae that are found in spinal fluid, urine, sputum, peripheral blood, and in the lungs. Another fly take a blood meal and ingests microfilariae. The microfilariae shed sheaths, penetrate fly’s midgut, and migrate to thoracic muscles. The L1 larvae forms and becomes an L3 larvae which migrates to the head and fly’s proboscis. The fly is now ready to infect another person
This Loa loa worm, measuring about 55 mm long, was extracted from the conjunctiva of a patient with loiasis. The Loa loa has a complex life cycle. Biting deerflies native to the rain forests of Central and West Africa transmit the larvae between humans. (credit a: modification of work by Eballe AO, Epée E, Koki G, Owono D, Mvogo CE, Bella AL; credit b: modification of work by NIAID; credit c: modification of work by Centers for Disease Control and Prevention)
  • Describe the most common way to diagnose loiasis.

Parasitic skin and eye infections

The protozoan Acanthamoeba and the helminth Loa loa are two parasites capable of causing infections of the skin and eyes. [link] summarizes the characteristics of some common fungal infections of the skin.

Table titled: Parasitic Skin and Eye Infections. Columns: Disease, Pathogen, Signs and Symptoms, Transmission, Antimicrobial Drugs. Acanthamoeba keratis, Acanthamoeba, Inflammation and damage to cornea; vision impairment or blindness, Exposure to pathogens in contaminated water or on contact lenses, Polyhexamethylene biguanide, chlorhexidine, azoles. Loiasis, Loa loa, Recurring fever and localized Calabar swelling, itching, and skin or eye pain during subcutaneous migration of worms, Larvae transmitted between humans by deerfly vector, Diethylcarbamazine, albendazole.

Key concepts and summary

  • The protozoan Acanthamoeba and the helminth Loa loa are two parasites that can breach the skin barrier, causing infections of the skin and eyes.
  • Acanthamoeba keratitis is a parasitic infection of the eye that often results from improper disinfection of contact lenses or swimming while wearing contact lenses.
  • Loiasis , or eye worm, is a disease endemic to Africa that is caused by parasitic worms that infect the subcutaneous tissue of the skin and eyes. It is transmitted by deerfly vectors.

Fill in the blank

Eye worm is another name for ________.

loiasis

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The ________ is the part of the eye that is damaged due to Acanthamoeba keratitis.

cornea

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Source:  OpenStax, Microbiology. OpenStax CNX. Nov 01, 2016 Download for free at http://cnx.org/content/col12087/1.4
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