Most insects and parasites that live on the human eye affect people living in tropical and developing countries, and travellers to these areas are at risk of being infected with these parasites. Other parasites can affect contact lens wearers who are particularly at risk of catching an infection from a protozoan that can live on poorly cared for lenses.
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This parasitical worm is caused by infected female blackfly bites. The worm causes onchocerciasis, commonly known as River Blindness. The Centers for Disease Control and Prevention (CDC) says that onchocerciasis is most common in rural African villagers who live by rapidly flowing streams. Travellers rarely get infected with this parasite because it takes more than a single bite from the blackfly to contract the condition. Microscopic worms spread across the human eye causing lesions. If the infestation is severe enough it can cause blindness.
There is no vaccine; however, medication can control the microscopic worms, decreasing the damage, says the CDC.
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The loa loa, also known as the African eyeworm, causes the loiais infection. Certain deerfly and mango fly bites transmit loa loa. The medical research site, Oriel, reports that humans are the only known hosts in which this parasite can reproduce. Loa loa can infect the brain and cause cause encephalitis. Loiasis can be treated with diethylcarbamazine which can control the larvae. Loiasis can also be treated with chemotherapy or by surgically removing the adult worms.
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This pork tapeworm causes the infection known as cysticerosis which prefers the brain and eyes. Found all over the world, this parasite is prevalent in areas where pigs are able to roam free. People can contract cysticerosis by ingesting the parasite's eggs through food, water or oral contact. In the human eye, these parasites cause blurred vision and may cause the eye to swell, subsequently causing the retina to detach. The CDC says that symptoms can occur months to years after the initial infection. Drugs and surgery are used to treat cysticercosis.
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Acanthamoeba live in fresh and marine water, air conditioners, hot tubs, shower heads, air and soil. Acanthamoeba are common and most people are exposed to them during their lifetime, says the CDC. Acanthamoeba cause the human eye infection, ancanthamoeba keratitis, which can lead to visual impairment or blindness. It most often affects people with improper contact lens hygiene or who wear their contact lenses while swimming or showering. Using tap water or homemade contact lens cleansing solution can also increase the risk of infection. Symptoms include eye irritation, eye pain, blurred vision and sensitivity to light. If acanthamoeba keratitis is diagnosed promptly, it can be treated effectively.
- "Clinical Microbiology Review", Fungal and Parasitical Infections of the Eye, Stephen Klotz et al, (2000, Oct. 13),
- Centers for Disease Control and Prevention, Parasitic Disease Information, River Blindness (Onchocerciasis),
- CDC, Parasitic Disease Information, Cysticercosis,
- CDC, Parasitic Disease Information, Acanthomoeba Infection FAQs