Medical Microbiology Study Guide for Optometry Students - Protozoa and Helminths - (1)

Inflammation of the retinal pigment epithelium and retinal vasculitis decreased vision, and panuveitis with secondary glaucoma can occur. Indirect ophthalmoscopy showed vitritis with plenty of vitreous membranes, and subretinal yellow lesions in the peripheral retina along with retinal pigment epithelial tracts [ 36 ]. An aqueous tap and a peripheral blood smear isolate microfilariae of W. Therapy with diethyl carbamazine citrate along with systemic steroids provides symptomatic relief. It is a known cause of neural larva migrans in animals [ 37 ]. It was identified in seven childhood cases manifesting as diffuse unilateral subacute neuroretinitis and choroidal infiltrates in association with neurologic disease.

Those children had a history of pica and raccoon exposure. Differences in inoculum level are likely responsible for isolated ocular larva migrans versus neural larva migrans in humans [ 38 ].

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Identification of the worm in the eye is the definitive diagnosis. Indirect immunofluorescence assays on serum, and cerebrospinal fluid is usually positive or serially positive and increasing [ 39 ]. Treatment is with albendazole and corticosteroids, and prognosis is usually poor. Dirofilaria are parasitic nematodes that are common in domestic and wild animals. Dirofilarial zoonotic infections are caused by mosquito vectors that carry the parasites from their animal hosts to people. As the worm matures, it elicits a host inflammatory response that ultimately produces the clinical presentation of a subcutaneous nodule.

These nodules are most often found on areas with exposed skin [ 41 ]. Subcutaneous dirofilariasis appears as a small subcutaneous nodule that gradually grows over periods of weeks or months. The consistency of the nodule is hard and elastic with marked erythema. When the location is ocular, the worms are situated in the conjunctiva and can be extracted by incision.

The diagnosis of dirofilariasis is established histopathologically. Both the gross and microscopic features of D. Once diagnosed, the recommended treatment is complete removal of the nematode. If the nematode is not removed, it eventually degenerates, and the mature granulomatous response results in either calcification or abscess formation with subsequent purulent expulsion of the parasite.

The agent of loiasis is Loa loa. Infection is acquired by humans through the bite of the tabinid flies of the genus Chrysops. When humans are bitten, larvae pass from the fly to the human, where they develop over 1year into mature adult worms [ 43 ]. These adults migrate through cutaneous and deep connective tissue, producing microfilariae.

Ocular disease may be due to both the presence of microfilaria and the presence of the adult worm. The diagnosis of loiasis is generally made by the detection of circulating microfilariae. In cases of conjunctival involvement, extraction of an adult worm confirms the diagnosis. Therapy of loiasis involves the manual removal of adult worms present in the conjunctiva in addition to the use of diethylcarbamazine DEC.

Severe hypersensitivity responses may occur due to the killing of both microfilariae and adult worms. It appears that humans are the main reservoir of onchocerciasis, with infection occurring from the bite of an infected female blackfly, Simulium spp. The disease is restricted to areas adjacent to river systems.

An estimated 37 million people in 34 countries in Sub-Sahara Africa and South America are affected by it [ 44 ]. After biting an infected person and ingesting microfilariae, the microfilariae mature to the larval stage as they migrate to the proboscis of the fly. There, the larvae may be injected into a human with the next bite, resulting in the formation of an adult worm capable of producing microfilariae. These microfilariae migrate throughout skin and connective tissue, where they die after several years. Adult worms may live in the subcutaneous tissue for years, with a female producing one-half to one million microfilariae yearly.

The site of the adult worm is usually found over a bony prominence and may develop into a firm, nontender nodule, or onchocercoma.

It is the migration of microfilariae through skin and connective tissue which is responsible for the majority of clinical findings in onchocerciasis. There are five predominant ocular findings that correlate with the location of microfilariae: Other findings may include distortion of the pupil, which may also be covered with exudate. Wolbachia and Wolbachia-derived molecules are bacterial symbionts of O. Experiments using Wolbachia-containing extracts of O. The diagnosis of onchocerciasis is accomplished by a combination of clinical symptoms and signs with histopathologic examination of specimens.

Slit lamp examination may confirm the presence of microfilariae in the anterior chamber. A sclerocorneal punch biopsy may aid in the diagnosis as well [ 47 ]. PCR may aid in the diagnosis of disease associated with a low burden of microfilariae. Xenodiagnosis, using laboratory-bred blackflies, may provide a clue as well.

Traditional therapy has centered on the use of DEC, but this is active only against microfilariae, allowing adult worms to repopulate the microfilariae in several months. This had led to dramatic improvements in disease control to the extent that elimination has become a realistic target [ 48 ]. Transmission of eyeworms occurs via nonbiting diptera that feed on the ocular secretions, tears, and conjunctiva of animals.

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4. Medical Microbiology Study Guide For Optometry Students Protozoa And Helminths 1.
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The disease, thelaziasis, is characterized by a range of subclinical to clinical signs such as epiphora, conjunctivitis, keratitis, corneal opacity, and ulcers [ 49 ]. The adult and larval stages are responsible for eye disease. Asymptomatic, subclinical thelaziasis occurs mainly when only the male nematodes parasitize animals, whereas evident symptoms have been more frequently registered in the presence of gravid females [ 50 ].

The lateral serration of the Thelazia cuticle causes mechanical damage to the conjunctival and corneal epithelium. Collected nematodes are identified based on morphologic key [ 51 ]. Fortreatment of human cases, the removal of the worm is suggested. Topical treatment with thiabendazole hasalso been reported to kill the worms. Larva migrans in man are a disease characterized by inflammatory reaction around or in the wake of migrating larvae, most commonly larvae of nematode parasites of other animals.

For some of the larva migrans producing larvae, man is merely an accidental but more or less normal intermediate or paratenic host. Toxocariasis is an important cause of unilateral visual loss and leukocoria in infants, and as a differential diagnosis of retinoblastoma. Visceral larva migrans are best known in the form produced by the larvae of Toxocara canis , these having been identified in autopsy specimens of lungs, liver, brain, and in several enucleated eyes [ 52 ].

Human infection by a spiruroid form of nematode Gnathostoma spinigerum has been reported sporadically from Thailand, the Philippines, China, Japan, and India. The high prevalence may be increasing in areas whereby freshwater raw fish is customary. Palpebral oedema with conjuctival erythema developed when lesions developed near the eye.

Intraocular parasites occur so rarely that they are considered as ophthalmological curiosities, nevertheless, it can cause intraocular hemorrhage, uveitis, and loss of vision within 2 days [ 53 ]. Following surgical removal, treatment is with albendazole and topical corticosteroids.

Trichinosis is a parasitic disease which probably presents itself for diagnosis not infrequently. Because of its varied symptomatology trichinosis is, unless by chance, almost as frequently undiagnosed. This is evidenced by the comparatively few cases reported in the literature. Ocular trichinosis can manifest itself as oedema of the face especially around the eyes, conjunctivitis, and exophthalmoses. Diagnosis is only confirmed by finding the worm in a section of the excised muscle see Tables 3 and 4. This helminthic infection caused by the larval cysts of the pork tapeworm Taenia solium.

Infection is often asymptomatic though neurological symptoms—predominantly seizures—are the most common manifestation. Ocular involvement is well recognised and includes orbital, intraocular, subretinal, and optic nerve lesions [ 54 — 57 ]. Cysticercosis can be evident as a free-floating cyst with amoeboid movements within the vitreous or anterior chamber of the eye.

Gaze palsies may also occur secondary to intramuscular cysts or cranial nerve lesions from intracerebral cysts. Diagnosis depends on imaging with ultrasound, MRI, and CT scanning all being useful, depending on the location of the cysts [ 58 , 59 ]. Serology can be useful but in cases of isolated cysts may be negative. Treatment is largely with the antihelminthic albendazole.

Antihelminthic therapy may lead to an increased inflammatory reaction around the lesions, and for this reason corticosteroids are often used when treating neurological or ocular disease. Spontaneous extrusion of cysts from the orbit may occur, and surgery may be required for isolated ocular lesions when they are growing and causing visual loss. Fasciola hepatica is a zoonotic helminth that is prevalent in most sheep-raising countries.

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The biliary duct of the liver is the main site of establishment of the parasite. However, immature flukes may deviate during migration, entering other organs, and causing an ectopic infestation [ 61 ]. In humans, ectopic locations in the orbit [ 62 , 63 ] have been reported. Identification of the route of entry of the parasite larva into the anterior chamber of the eye is difficult. One possible route can be via the central retinal artery into the vitreous, causing vasculitis and endophthalmitis [ 64 ].

Severe intraocular reaction, haemorrhage, diffuse vasculitis, and retinal ischaemia of the patient may be caused as a result of the presence or irritation of the parasite. Early vitrectomy and removal of the parasite resulted in a rapid response, with reasonable final visual acuity. Definitive preoperative diagnosis is difficult [ 67 ]. Laboratory and immunologic tests are generally unhelpful.

From the literature and our own observations, orbital hydatid cysts usually appear as a well-defined, thin-walled, oval shape lesions with fine peripheral rim enhancement of their fibrous capsule after contrast medium administration [ 68 ]. Various theories have been postulated as to the different routs by which the schistosoma ova or even the adult worms can reach the systemic circulation and then after lodged in ectopic sites such as the eyes. Cercariae the infective stage develop to maturity and lay their eggs in the veins directly under the skin or the mucous membrane through which they have penetrated if the part is richly vascularised [ 69 ].

The presence of schistosomal eggs in the eye can produce granuloma formation and inflammatory sequelae [ 70 ]. Considering how common the infection is in endemic areas, involvement of the eye is incredibly rare. Effective treatment, using the drug praziquantel, has been available for 25 years, but the growth of human populations in high-risk areas, as well as the high probability of rapid re-infection after treatment, has thwarted efforts to control the number of human infections worldwide [ 71 ] see Tables 5 and 6. Ocular myiasis is the result of invasion of the eye by larvae of flies.

Ophthalmomyiasis may be categorized into three categories: Ophthalmomyiasis externa is usually seen in areas of shepherding and is typically due to larvae of the sheep nasal botfly, Oestra ovis [ 73 ].

A crawling or wriggling sensation accompanied by swelling and cellulitis may be seen in palpebral myiasis. Ophthalmomyiasis interna is most commonly caused by a single larva of the Hypoderma spp. Infection is due to invasion of the tissues, leading to uveitis. More serious complications may include lens dislocation and retinal detachment [ 74 ]. Orbital myiasis may be due to a number of fly species and is generally seen in patients who are unable to care for themselves [ 75 ]. Diagnosis of ophthalmomyiasis is made by demonstration of maggots, and histologic examination may show granuloma formation.

Anticholinesterase ointment may help kill or paralyze the larvae. Steroids and antibiotics may be necessary to control inflammation and secondary bacterial infection. Lice belong to the order Anoplura. Of these, medically important species include Pediculus humanus var. Depending on the species, eggs, or nits, are laid and glued to body hairs or clothing fibers. Following this, nymphs emerge to feed on the host, giving rise to symptoms of pruritis.

Of the species mentioned, P. In addition to pruritis, small erythematous papules with evidence of excoriation may be present. Involvement of the eyelash may cause crusting of the lid margins. In this case, diagnosis is relatively simple as nits are easily seen at the base of the eyelash [ 76 ].

Ticks are arthropods belonging to the class Arachnida. There are a number of different species of ticks which may cause disease in humans and animals. Ticks exist in three life stages—larva, nymph, and adult—all of which requires blood meals. Most tick bites are uncomplicated, and prompt removal of the tick is all that is necessary [ 78 ].

Ticks have been reported to attach to ocular structures. In one such case, the nymph was associated with a stinging sensation [ 79 ].

Immunity to Parasitic Infection

Following the removal of the tick, a firm nodule, representing a tick bite granuloma, may remain for several weeks. This granuloma likely represents retained tick material and generally resolves spontaneously. The majority of the clinically important species of parasites involved in eye infections are reviewed in this paper.

Emphases have been placed on literatures published within the past decade, but prior noteworthy reviews and case reports are included. We searched the MEDLINE database via PubMed and identified articles by cross-referencing the terms ocular, eye, ophthalmic, retinitis, endophthalmitis, conjunctivitis, and uveitis to specific infectious diseases in adults. We searched the Cochrane database for systematic reviews on the treatment of specific parasitic ocular infections. Additionally, we reviewed texts for completeness and to obtain other references of eye complications of systemic infections see Tables 7 and 8.

Interdisciplinary Perspectives on Infectious Diseases. Subscribe to Table of Contents Alerts. Table of Contents Alerts. Abstract Ocular parasitosis in human is more prevalent in geographical areas where environmental factors and poor sanitary conditions favor the parasitism between man and animals. Introduction Ocular parasitosis in human is more prevalent in geographical areas where environmental factors and poor sanitary conditions favor the parasitism between man and animals. Protozoan Eye Infection 2. Acanthamoeba Keratitis Acanthamoeba spp.

Malaria Caused by the Plasmodium species and transmitted via the bite of the female anopheles mosquito, this sometimes fatal infectious disease has characteristic findings in the eye. Microsporidiosis Two genera appear to be important in the pathogenesis of ocular disease: Toxoplasmosis Toxoplasma gondii is a protozoan parasite, the lifecycle of which passes through cats.

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