Ocular parasitosis in human is more prevalent in geographical areas where environmental factors and poor sanitary conditions favor the parasitism between man and animals. Lesions in the eye can be due to damage directly caused by the infectious pathogen, indirect pathology caused by toxic products, or the immune response incited by infections or ectopic parasitism. The epidemiology of parasitic ocular diseases reflects the habitat of the causative parasites as well as the habits and health status of the patient. An ocular examination may provide clues to the underlying disease/infection, and an awareness of the possibilities of travel-related pathology may shed light on an ocular presentation. This paper is a comprehensive review of the parasitic diseases of the eye. The majority of the clinically important species of parasites involved in eye infection are reviewed in this paper. Parasites are discussed by the disease or infection they cause.
Ocular parasitosis in human is more prevalent in geographical areas where environmental factors and poor sanitary conditions favor the parasitism between man and animals. In recent years, population shift and rapid transport have facilitated the spread of certain parasitic diseases from endemic to nonendemic areas. The routes of infection to man vary with species of the parasite and the animal hosts they infest. Lesions in the eye can be due to damage directly caused by the infectious pathogen, indirect pathology caused by toxic products, immune response incited by infections, or ectopic parasitism of the preadult or adult stages.
The epidemiology of parasitic ocular diseases reflects the habitat of the causative parasites as well as the habits and health status of the patient. Additional consideration must include local sanitation and the presence of a vector for transmission as well as the more complicated life cycles of the parasites and definitive hosts. Dietary history should be considered since most parasitic transmission is through food and water contamination. Travel history to endemic areas is important to determine the source of infection. An awareness of these is therefore important to the clinician evaluating this group of patients.
An ocular examination may provide clues to the underlying disease, and an awareness of the possibilities of travel-related pathology may shed light on an ocular presentation. The eye is involved both in a variety of systemic infections and may be the primary focus of other pathologies. The majorities of conditions affecting the eyes—other than injuries—are infectious.
In some occasions, the ophthalmic lesions occur as a result of antiparasitic treatment as it has been noticed in the prophylactic and therapeutic attempts to treat malaria [
Despite improved understanding of the clinical features of inflammatory eye diseases and advances in diagnostic testing, clinicians should maintain a high index of suspicion for infective parasitic diseases in patients thought to have inflammatory eye involvement.
Because of this somehow more complex scenario, and the tendency for the parasites to cause a wider variety of pathologic lesions, the various parasitic etiologies of ocular diseases will be addressed individually, including epidemiology, pathology, diagnosis, and treatment.
There are two stages in the life cycle of this environmental ameba: the motile trophozoite (8–40
The leading risk factors for
A provisional diagnosis of AK can be made using the clinical features and confocal microscopy although a definitive diagnosis requires culture, histology, or identification of
Chagas’ disease, or American trypanosomiasis, results from infection by
The diagnosis of acute Chagas’ disease is made by the detection of trypomastigotes in the bloodstream by direct examination of uncoagulated blood or buffy coat preparation. Direct culturing of blood on Novy, MacNeal, Nicolle’s medium (NNN) or other suitable media may result in positive cultures in 7to 10days [
Therapy of Chagas’ disease with antitrypanosome therapy is most successful in the acute stage. Two medications are available: nifurtimox and benznidazole. Therapy is usually extended for a period of months, and parasitologic cure rates are somewhat disappointing. Both medications carry a long list of significant side effects.
The protozoan disease giardiasis can cause ocular complications, including “salt and pepper” retinal changes. One study showed that asymptomatic, nonprogressive retinal lesions are particularly common in younger children with giardiasis. This risk does not seem to be related to the severity of the infection, its duration, or the use of metronidazole but may reflect a genetic predisposition [
Diagnosis is confirmed by finding the cyst stage in the fecal smear. Treatment is the same as for intestinal infection, that is, metronidazole.
Once injected into humans during the sandfly blood meal, the promastigote develops into an amastigote after being engulfed by tissue macrophages. Within these cells, the amastigotes replicate and may spread either systemically or cutaneously.
Visceral leishmaniasis, or that which represents systemic disease, is known as kala-azar. The ocular manifestations of kala-azar are relatively uncommon and include chorioretinitis, central retinal vein thrombosis, iritis, papillitis, and keratitis [
Ocular findings in cutaneous leishmaniasis represent a local phenomenon resulting from the initial site of infection near the eye with occasional spread to the lacrimal duct. Ptosis may be a presenting complaint [
The diagnosis of leishmaniasis is made by direct demonstration of organisms on tissue smears or biopsy. Amastigotes are usually demonstrated fairly easily in the case of cutaneous or mucocutaneous ocular disease. However, amastigotes have not been directly identified in cases of ocular disease associated with kala-azar. When present,
Treatment of choice is pentavalent antimony, sodium stibogluconate 15–20 mg per kg per day IM or IV for 15–20 days. A second or even a third treatment course with pentavalent antimonal can be given over 6–8 weeks if healing is not progressive.
Caused by the
Quinacrine and chloroquine are molecules with the same alkyl side chain but different nuclei. The photobiological effects of quinacrine and chloroquine are similar in model systems; thus, development of a bull’s-eye maculopathy with quinacrine ingestion is an unsurprising potential side effect.
The definitive diagnosis of malaria is made by microscopic identification of the parasite in the blood smear. A thin blood film should be examined for at least 15 minutes, whereas a 5-minute search of a thick film should reveal parasites if present. The thick film is the most efficient method of detecting malarial parasites, but interpretation requires an experienced worker.
Antimalarial drugs may be classified as (1) suppressive, by acting upon asexual blood cell stages and preventing the development of clinical symptoms; (2) therapeutic, by also acting on asexual forms to treat the acute attack; (3) radical cure, for destruction of the EE forms; (4) gametocytocidal, for destroying gametes; (5) sporoniticidal, for drugs that render gametocytes noninfective in the mosquito.
Two genera appear to be important in the pathogenesis of ocular disease:
Ocular infection is presumed to occur either by direct inoculation into eye structures or by dissemination systemically, with the latter proposed to be the pathogenesis in patients with AIDS. Ocular findings are generally limited to the conjunctiva and cornea.
With respect to diagnosis, spores have been demonstrated in most cases in which corneal scrapings or biopsy specimens are examined by light or electron microscopy. Where available, serologic testing may assist in the diagnosis of microsporidiosis.
Current recommendations for treatment include the use of albendazole, which has shown some promise in the treatment of corneal disease. Historically, severe, progressive cases of ocular microsporidiosis have resulted in enucleation.
Rhinosporidiosis, caused by
At present, the treatment for rhinosporidiosis is the surgical excision. Some authors proposed a medical therapy with dapsone [
Toxoplasma gondii is a protozoan parasite, the lifecycle of which passes through cats. It represents the commonest cause of uveitis worldwide [
Some patients may present with a glandular fever-like systemic febrile illness with adenopathy. Most cases of adult infection will not present with eye signs, those that do usually present with a focal necrotising retinitis occasionally associated with vascular occlusion [
Serologic tests are very important in the diagnosis of toxoplasmosis. Because of the common occurrence of antibodies to the parasite in the general population, diagnosis by serologic means requires the demonstration of a significant increase in antibody titers.
Drug treatment for ocular and cerebral toxoplasmosis is the same and lesions will continue to grow without therapy. Clindamycin and azithromycin are now commonly used as first line treatment. Azithromycin has been shown to be effective in reducing the number of attacks in Brazil (see Tables
Ocular parasitosis caused by protozoa (
Disease/Infection | Causative agent | Geographical distribution | Ocular findings |
---|---|---|---|
Acanthamoebic keratitis |
|
Worldwide, soil and water | Conjuctival oedema, sever pain, ring infiltrate around the cornea, hypopyon, hyphema, uveitis, loss of vision |
| |||
Chagas' disease |
|
Central and South America | Palpebral and periorbital oedema |
| |||
Giardiasis |
|
Southeast Asia, Europe, USA and South Africa | Salt and pepper retinal changes, chorioretinitis, retinal haemorrhage and uveitis |
| |||
Leishmaniasis |
|
Africa, Mediterranean region, Middle East, parts of Asia and Central and South America |
|
| |||
Malaria |
|
Africa, Central and South America, Oceania and Asia | Retinal haemorrhage, papilloedema, cotton wool spots |
| |||
Microsporidiosis |
|
Worldwide | Conjunctival hyperemia, punctate epithelial keratitis, hyphema, necrotizing keratitis, corneal ulcer |
| |||
Rhinosporidiosis |
|
South America and Africa | Cojuctival granuloma |
| |||
Toxoplasmosis |
|
Worldwide, South America | Congenital: strabismus, nystagmus and blindness |
Ocular parasitosis caused by protozoa (
Disease/Infection | Diagnosis | Treatment |
---|---|---|
Acanthamoebic keratitis | Corneal scrapings, culture | Propamadine (0.1% solution) + antibacterial preparation, polyhexamethylene biguanide (0.02% solution), chlorhexidine (0.02% solution), keratoplasty. |
| ||
Chagas' disease | Blood smear, Buffy coat*, culture, Xenodiagnosis* | Nifurtimox, benznidazole |
| ||
Giardiasis | Diagnosing intestinal disease and exclusion | Metronidazole, albendazole, paromomycin |
| ||
Leishmaniasis | Tissue smears or biopsy, culture in NNN medium | Antimonials, amphotericin B, Paromomycin, Fluconazole, zinc sulfate |
| ||
Malaria | BFMP*, Buffy coat, PCR, serological | Chloroquine, Primaquine, Dapsone, Mefloquine, artemisinin derevatives |
| ||
Microsporidiosis | Corneal scrapings, biopsy, serological | Albendazole |
| ||
Rhinosporidiosis | Histopathologic demonstration | Dapsone, amphotericin B |
| ||
Toxoplasmosis | Serology (IgM, IgG), PCR | Clindamycin+ azithromycin, pyrimethamine+ sulfadiazine, |
*Buffy coat: The thin layer of concentrated white blood cells that forms when a tube of blood is spun in a centrifuge.
*Xenodiagnosis: a method of animal inoculation using laboratory-bred bugs and animals.
*BFMP: Blood Film for Malaria Parasite.
Ocular angiostrongyliasis, caused by
Although blood eosinophilia is demonstrated in most cases of eosinophilic meningitis [
Although a wide range of initial visual acuity was reported, from finger count to 6/6, five cases had visual acuity less than 2/60. The duration of visual impairment varied from 4 days to 8 weeks, mostly 2-3 weeks. Additionally, indirect ophthalmoscopy should be recommended in any individual presenting with a history of eating raw
Any types of laser, surgical removal, and corticosteroid treatment did not improve visual acuity. Alteration of the retinal pigment epithelium or retinal inflammation caused directly by parasites was the main reasons for poor vision at presentation. Furthermore, it produced permanent damage to an affected eye and gave a poor outcome. Although corticosteroids and albendazole have been reported to be effective in ocular cysticercosis and neurocysticercosis [
Human ocular infestation by live filarial worm is a rare occurrence and has been reported mostly from South-East Asia. It involves the eyelids, conjunctiva, cornea, anterior chamber, and uvea. Ocular filariasis can present in an otherwise asymptomatic patient without any constitutional symptoms. 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 [
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 [
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. Although these infections remain rare, they are increasing in incidence and human dirofilariasis may be considered an “emergent zoonosis [
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 [
The diagnosis of dirofilariasis is established histopathologically. Both the gross and microscopic features of
The agent of loiasis is
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,
It is the migration of microfilariae through skin and connective tissue which is responsible for the majority of clinical findings in onchocerciasis. Ocular onchocerciasis is due to the presence and/or migration of microfilariae in and through ocular structures as well as the host’s response to the migration [
Wolbachia and Wolbachia-derived molecules are bacterial symbionts of
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 [
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.
Ivermectin is the treatment of choice and mass distributed by the WHO Onchocerciasis Control and the Onchocerciasis Elimination Programme for the Americas. This had led to dramatic improvements in disease control to the extent that elimination has become a realistic target [
Transmission of eyeworms occurs via nonbiting diptera that feed on the ocular secretions, tears, and conjunctiva of animals. The disease, thelaziasis, is characterized by a range of subclinical to clinical signs such as epiphora, conjunctivitis, keratitis, corneal opacity, and ulcers [
Collected nematodes are identified based on morphologic key [
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.
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
Ocular parasitosis caused by round worms (
Disease/Infection | Causative agent | Geographical distribution | Ocular findings |
---|---|---|---|
Angiostrongyliasis |
|
Southeast Asia, Pacific region, eastern Australia | Blurred vision and poor visual acuity |
| |||
Bancroftian and Brugian filariasis |
|
Southeast Asia | Retinal vasculities, decreased vision and panuveitis with secondary glaucoma |
| |||
Baylisascariasis |
|
Few records in US, Japan, Germany | Vision loss, transient visual obscuration, and diffuse unilateral subacute neuroretinitis |
| |||
Dirofilariasis |
|
Europe, Asia and Africa | Pain, oedema, and congestion of the conjunctiva, diplopia, foreign body sensation in the eye |
| |||
Loiasis |
|
Central and West Africa | Conjunctival congestion and pain with movement of the eye. May affect vision transiently. Retinal hemorrhages and perivascular inflammation |
| |||
Onchocerciasis |
|
Tropical Africa, South America, and the Arabian peninsula | Chorioretinitis, keratitis, uveitis, corneal opacification, neovascularisation, blindness |
| |||
Thelaziasis |
|
Asian Pacific region | Epiphora, conjunctivitis, keratitis, corneal opacity and ulcers |
| |||
Toxocariasis |
|
Wide spread | Peripheral white mass is often visible in affected eyes |
| |||
Trichinosis |
|
Central and eastern Europe, united States | Oedema around the eye, conjunctivitis and exophthalmoses |
Ocular parasitosis caused by round worms (
Disease/Infection | Diagnosis | Treatment |
---|---|---|
Angiostrongyliasis | Identification of |
Oral and topical prednisolone, laser treatment, surgical removal of the parasite |
| ||
Bancroftian and Brugian filariasis | An aqueous tap and a peripheral blood smear isolate microfilariae or adult worm | Carbamazine citrate along with systemic steroids |
| ||
Baylisascariasis | Exclusion of other known causes of OLM* | Steroids and antihelminthic agents |
| ||
Dirofilariasis | Excision biopsy |
Surgical excision of the adult worm, DEC* |
| ||
Loiasis | Extraction of adult worm or microfilaria | Manual removal of adult worm or microfilaria present in the conjunctiva and DEC |
| ||
Onchocerciasis | Slit lamp, sclerocorneal punch biopsy, Xenodiagnosis | Manual removal of adult worms, ivermectin or mebendazole |
| ||
Thelaziasis | Eggs or larvae can be seen when tears or other eye secretions are examined under light microscope | Surgical |
| ||
Toxocariasis | Serology | Cryopexy and photocoagulation, albendazole and corticosteroid |
| ||
Trichinosis |
Muscle biopsy | Thiabendazole, mebandazole, steroids |
This helminthic infection caused by the larval cysts of the pork tapeworm (
Diagnosis depends on imaging with ultrasound, MRI, and CT scanning all being useful, depending on the location of the cysts [
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.
Hydatid cysts are most commonly seen in the liver (60–70%) and lungs (20%) [
Definitive preoperative diagnosis is difficult [
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 [
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 [
Ocular parasitosis caused by flat worms (
Disease/Infection | Causative agent | Geographical distribution | Ocular findings |
---|---|---|---|
Cysticercosis |
|
Mexico, Central America, Indian subcontinent, Far East and Africa | Subconjunctival and eyelid masses, papilloedema, cranial nerve palsies, vitritis and optic neuritis |
| |||
Fascioliasis |
|
Africa and Asia | Painful red eye, and there may be visual defect |
| |||
Hydatid cyst |
|
South America, Australia, Middle East and Mediterranean countries | Orbital swelling, exophthalmus and proptosis |
| |||
Schistosomiasis |
|
Sub-Sahara Africa, China, South Asia | Uveitis and subretinal granuloma |
Ocular parasitosis caused by flat worms (
Disease/Infection | Diagnosis | Treatment |
---|---|---|
Cysticercosis | Imaging with ultrasound, MRI and CT |
Albendazole, corticosteroids |
Fascioliasis | Adult worm in the eye | Vitrectomy and removal of the parasite |
Hydatid cyst | Imaging | Surgical removal |
Schistosomiasis | Eggs in the feces, urine or eggs/cercariae in the eye | Praziquantel |
Ocular myiasis is the result of invasion of the eye by larvae of flies. Genera important to human myiasis include
Ophthalmomyiasis externa is usually seen in areas of shepherding and is typically due to larvae of the sheep nasal botfly,
Ophthalmomyiasis interna is most commonly caused by a single larva of the
Orbital myiasis may be due to a number of fly species and is generally seen in patients who are unable to care for themselves [
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
Eyelid disease is treated with a thick layer of petrolatum twice a day for 8days, or the application of 1% yellow oxide of mercury four times a day for 2 weeks [
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 [
This is a comprehensive paper of the parasitic diseases/infections of the eye. The majority of the clinically important species of parasites involved in eye infections are reviewed in this paper. Parasites are discussed by the disease or infection they cause. 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
Ocular parasitosis caused by ectoparasites (
Disease/Infection | Causative agent | Geographical distribution | Ocular findings |
---|---|---|---|
Myiasis |
Larvae of flies | Shepherding places | Uveitis, lens dislocation and retinal detachment |
Phthiriasis palpebrum |
|
Cosmopolitan | Crusting of the eyelid margins |
Tick infestation | Hard and soft ticks | Cosmopolitan | Stinging sensation |
Ocular parasitosis caused by ectoparasites (
Disease/Infection | Diagnosis | Treatment |
---|---|---|
Myiasis |
Demonstration of maggots, histological examination | Manual removal of the maggots, anticholinesterase ointment |
Phthiriasis palpebrum |
Nits seen at the base of eyelashes | Manual removal of the lice and nits, thick layer of petrolatum, 1% yellow oxide of mercury |
Tick infestation | Biomicroscopy may reveals ticks embedded in conjunctiva, eyelid margins or crawling on the eyelashes | Removal by conjunctival excision |