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Nematode Infections of the Eye: Toxocariasis, Onchocerciasis, Diffuse Unilateral Subacute Neuroretinitis, and Cysticercosis

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Nematode Infections of the Eye: Toxocariasis, Onchocerciasis, Diffuse Unilateral Subacute Neuroretinitis, and Cysticercosis Ophthalmol Clin N Am 15 (2002) 351–356 Nematode infections of the eye: toxocariasis, onchocerciasis, diffuse unilateral subacute neuroretinitis, and cysticercosis Nelson Alexandre Sabrosa, MD a,b,*, Moyse´s Zajdenweber, MD c,d aDepartment of Ophthalmology, University of Sa˜o Paulo, FMUSP, Sa˜o Paulo, Brazil bOphthalmology Department, Clı´nica Sa˜o Vicente, Rua Joao Borges, 204-Gavea, CEP 22451-100, Rio de Janeiro, Brazil cDepartment of Ophthalmology, Federal University of Sa˜o Paulo, Paulista School of Medicine, Sa˜o Paulo, Brazil dOphthalmology Department, Instituto Brasileiro de Oftalmologia, Praia de Botafogo 206, Botafogo, Rio de Janeiro, Brazil Ocular toxocariasis may cause a large spectrum of illitis, each of which can lead to loss of vision in the manifestations in the eye, from an asymptomatic affected eye [7]. posterior granuloma, to total retinal detachment [1]. It represents one of the most common parasitic causes Epidemiology of visual loss throughout the world [2], and it usually affects young children. Other nematodes can cause Human toxocariasis is probably one of the most ocular disease, most of them related to adult large widespread zoonotic nematode infections, occurring worms. Diffuse unilateral subacute neuroretinitis mainly in areas where the relationship between man, (DUSN) is a more recently described disorder soil, and dog is particularly close [8]. T canis is an believed to be caused by smaller nematodes [3,4]. often encountered canine parasite, affecting dogs, Onchocerciasis and cysticercosis are seen mainly in wolves, foxes, and other canidis, whereas T catis the developing world. may be found in domestic cats [9–11]. Human beings are contaminated through ingestion of the ova by geophagia, by eating contaminated foods, or by close Toxocariasis contact with puppies. Toxocariasis may manifest itself in the systemic form, visceral larva migrans, Wilder first recognized nematodes as pathogens in or the ocular form, ocular larva migrans. It is rare to the posterior segment of the eye in 1950. In 1952 see the ocular and visceral forms of the disease at the Beaver et al described the association of Toxocara same time. species with human disease [5]. Toxocariasis is a zoonotic disease caused by the infestation of humans Ocular toxocariasis by second-stage larva of the dog nematode Toxocara canis or the cat nematode T cati [6]. Ocular toxocar- Clinical features iasis may affect the eye causing uveitis, posterior and Toxocara is a well-documented cause of intra- peripheral retinochoroiditis, endophthalmitis, or pap- ocular inflammation in children [11]. Clinical pre- sentation depends on the primary tissue or anatomic site of involvement, which may include the peripheral retina, the vitreous, the posterior pole, or the optic * Corresponding author. Ophthalmology Department, Clı´nica Sa˜o Vicente, Rua Joao Borges, 204-Gavea, CEP disk. The most common presentation involves peri- 22451-100, Rio de Janeiro, Brazil. pheral retina and vitreous, occurring separately or E-mail address: [email protected] together. A hazy white lesion may be seen or in the (N.A. Sabrosa). periphery, often with moderate vitreitis. As the 0896-1549/02/$ – see front matter D 2002, Elsevier Science (USA). All rights reserved. PII: S0896-1549(02)00024-X 352 N.A. Sabrosa, M. Zajdenweber / Ophthalmol Clin N Am 15 (2002) 351–356 inflammation resolves, a peripheral elevated white imaging techniques, such as ultrasonography, ultra- mass is seen better, and is typically associated with sound biomicroscopy, CT, or MRI studies, may be retinal folds extending toward the macula [12,13]. An helpful [5,14,15]. intraretinal or subretinal mass, or granuloma, is Treatment options for T canis infection depend on usually seen with the posterior form of disease. the type and severity of infection. Management of the Endophthalmitis, with mild or no anterior inflam- systemic form of toxocariasis includes the use of mation, is an uncommon but recognized presentation. systemic anthelmintic agents, antibiotics, or cortico- Papillitis can also occur, and it is usually caused by steroids [7]. In patients with ocular toxocariasis, one an invasion of the optic nerve by the nematode or as must have in mind the visual potential of the eye, the an inflammatory response to the organism in another amount of active inflammation, and the degree of site of the eye. The condition is almost always macular damage. In eyes with active vitreitis, sys- unilateral and it usually affects children, but also temic or periocular corticosteroids may represent an can be seen in adults [7]. important therapeutic tool. Anthelminthics may be used to destroy nematodes and eliminate further Pathogenesis and differential diagnosis migration of the larva, but the parasite may resist Sprent first described the T canis life cycle in 1958 such treatment. In some situations, such as to clear [5]. As mentioned previously, it is a canine round- vitreous debris, relieve vitreomacular traction, repair worm sharing certain characteristics with the feline tractional and tractional-rhegmatogenous retinal roundworm T catis and with the human roundworm detachments, and remove the posterior hyaloid, pos- Ascaris lumbricoides [5]. Ingested Toxocara eggs terior vitrectomy can be performed [16–18]. emerge in the duodenum. The larvae then perforate the intestinal wall, enter the circulation, and can lodge in the eye, most probably by the choroidal blood Onchocerciasis system. Thereafter the organism can migrate into the subretinal space or vitreous cavity, where it ultimately Onchocerciasis, also named river blindness or dies and is encapsulated by an eosinophilic granu- Robles disease, is a parasitic disease caused by the lomatous inflammatory reaction [4]. microfilariae Onchocerca volvulus [19]. O volvulus Leukocoria is a frequent finding in patients with is transmitted by the bite of the black Simulium ocular toxocariasis. The differential diagnosis includes fly, which breeds in rapidly flowing waters. The retinoblastoma, endophthalmitis, retinopathy of pre- clinical manifestations of onchocerciasis range from maturity, congenital cataracts, persistent hyperplasic no skin or eye lesions to very severe skin involvement primary vitreous, Coats’ disease, and various forms of and blindness. trauma [10,12,13]. Laboratory investigations and therapy Epidemiology Leukocytosis and hypereosinophilia are present in most patients with visceral larva migrans. Eosino- Onchocerciasis is an endemic disease in Africa philia is usually absent in ocular toxocariasis. The and Central America, but pockets of the disease also presence of larva can be disclosed by tissue biopsy, exist in South America. In Africa, the clinical and but because the larvas are rarely able to finish their epidemiologic characteristics are different from other life cycle in humans, they are not detected on stool places. In the savannas, for example, about 40% of analysis. Until the use of the enzyme linked immu- the patients fewer than 40 years old develop blind- nosorbent assay (ELISA) test, immunodiagnostic ness [20]. Because of the high prevalence of this tests lacked sufficient sensitivity and specificity for disease in Africa it has become one of the main the diagnosis of ocular toxocariasis. In recent times, causes of blindness worldwide. According to the however, ELISA has become the main serologic World Health Organization, onchocerciasis affects at method for detecting visceral larva migrans, and for least 18 million people worldwide, and 300,000 are confirming the clinical suspicion of ocular toxocar- blind from the disease [21]. In Central America, the iasis. ELISA has a reported sensitivity of 78% and a clinical presentation seems to be the same, but ocular specificity of 92%, but it is known that the sensitivity involvement occurs earlier. In Brazil, for example, the and specificity of ELISA vary according to the cutoff disease occurs in the Yanomanis Indians in the north titer chosen defined as positive [14]. Most of the part of the country [22]. In this population, the ocular cases of ocular toxocariasis are diagnosed clinically, findings seem to be restricted to the cornea and but in some patients with opaque media radiologic blindness tends not to occur [23]. N.A. Sabrosa, M. Zajdenweber / Ophthalmol Clin N Am 15 (2002) 351–356 353 Ocular features Epidemiology The ocular manifestations of onchocerciasis are Initially described in the Southeastern and Mid- caused by the presence of dead parasites within the western parts of the United States and the Caribbean eye. The microfilariae penetrate the eye by the bulbar islands, DUSN has also been reported in other parts conjunctiva at the limbus, then invade the cornea, of North America, in South America, and in North- aqueous humor, and iris. They reach the posterior western Europe [29,30]. In Brazil DUSN is consid- segment by the circulation or ciliar nerves, which ered an important cause of posterior uveitis in supply the peripheral retina and choroid. children and young healthy adults [34–37]. Puntate keratitis is often the first manifestation of onchocerciasis, the patient referring only to conjunc- Clinical features tival itching. The microfilariae then migrate to the cornea and eventually die causing a corneal opacity Because prompt treatment may prevent visual referred to as cracked-ice or snowstorm.Inlate loss, it is very important that the diagnosis of DUSN stages, the corneal lesions turn to scar tissue pro- be made early. Most patients with DUSN, however, ducing sclerosing
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