Short CommunicationExperimental Pathology and Health Sciences

2015;7 (2): 5-6

Human ophtalmologic infections caused by visceral larva migrans

Rafael Santos 1, Teresa Mateus 1, 2, 3, 4, Ana Calado1, 5

AbstractZoonotic Toxocara eggs are excreted by dogs and cats. A ubiquitous distribution and resistance may lead to human, mainly children, accidental ingestion of embryonated eggs and infection. In humans the infection remains occult, often resulting in disease caused by the migration larval stages. Human infec-tion by Toxocara canis or Toxocara cati may progress to systemic and ocular toxocariasis. Specifically, it has been observed that systemic toxocariasis, also called visceral larva migrans, tends to affect children younger than 3 years of age, whereas ocular toxocariasis typically presents in older children and young adults. Most ocular damage results from the inflammatory response that occurs following larval death that eventually may progress to blindness. The diagnosis of ocular toxocariasis can be challenging since it´s a rare disease with prevalence less than 1% with variable clinical presentation.

PARASITE BIOLOGYToxocara canis accomplishes its life cycle in dogs, with humans acquiring the infection as an accidental host [1, 2]. Unembryonated eggs are shed with the feces of the dog [1, 2]. Eggs embryonate and become infective in the environment [2]. Following ingestion by dogs, the infective eggs hatch and larvae penetrate the gut wall [2]. In younger dogs, the larvae migrate through the lungs, bronchial tree, and esophagus becoming sexually mature adult worms in the small intestine [2]. In older dogs, pat-ent infections can also occur, but larval cysts in tissues are more common [2]. Encysted stages are reactivated in female dogs during late pregnancy and pass to the offspring through placenta, and less by lactation, to the puppies small intestine where adult worms become es-tablished. Puppies are a major source of environmental egg contamination. Toxocara canis can also be transmit-ted to dogs when they eat paratenic hosts like rabbits with parasite cysts [3].Humans are accidental hosts who become infected by the ingestion of infective eggs in contaminated soil or infected paratenic hosts [1, 3-5]. After ingestion, the eggs hatch and larvae penetrate the intestinal wall and are carried by the circulation to a wide variety of tissues like liver, heart, lungs, brain, muscle and eye[3]. The two main clinical pre-sentations of toxocariasis are visceral larva migrans and ocular larva migrans [6-10]. Diagnosis is usually made by serology or the finding of larvae in biopsy or autopsy specimens [3]. Toxocara cati has a similar life cycle but vertical transmission is essentially by lactogenic route from the queen to kittens [4, 11].

CLINICAL ASPECTSOcular toxocariasis is unilateral in 90 percent of patients [12]. The condition has traditionally been taught to affect primarily infants and young children, but recent surveys have reported Toxocara infections in a number of teenag-ers and young adults, as well [12]. Common symptoms that bring patients to the clinic include blurred vision and floaters [12, 13]. Pain and photophobia may also be pres-ent but are typically mild [12]. In young patients, the eye infection may not be noticed until they fail a school vi-sion screening test, or develop strabismus or leukocoria [8, 12]. The most serious consequence of the infection is invasion of the retina, leading to granuloma formation, which occurs typically peripherally or in the posterior pole [12]. These granulomas drag the retina and create a dis-tortion, heteropia, or detachment of the macula [3]. This pathology can also cause diffuse endophthalmitis or pap-illitis with secondary glaucoma and chorioretinitis [3]. Less than 25 percent of eyes with toxocariasis present with dense vitreous inflammation mimicking endophthalmitis. Interestingly ocular toxocariasis present with minimal or absent pain and photophobia and anterior or posterior synechiae [8]. Fundus visualization through the vitreous inflammation is usually difficult. Severe cases may de-velop an exudative retinal detachment. As the inflamma-tion subsides, vitreous membranes may organize into a retrolental mass, which in severe cases can produce cili-ary body detachment, hypotony and irreversible damage [8]. Infection with T. cati was implicated in a further case where decreased visual acuity was caused by a lesion in the macula of the eye [11].Prevention of toxocariosis and control strategies address-ing the dog and cat population

1 Departamento de Medicina Veterinária, Escola Universitária Vasco da Gama, Coimbra, Portugal2 Escola Superior Agrária de Ponte de Lima, Instituto Politécnico de Viana do Castelo, Ponte de Lima, Portugal 3 EpiUnit, Instituto de Saúde Pública da Universidade do Porto, Porto, Portugal4 CECAV - Centro de Estudos em Ciência Animal e Veterinária, Universidade de Trás-os-Montes e Alto Douro, Vila Real, Portugal5 Centro de Química da Universidade de Coimbra

Experimental Pathology and Health Sciences

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Toxocara spp. eggs are very resistant to adverse environ-mental conditions and remain infective for years [1, 5, 10, 14]. Since no practical methods exist for environmental egg reduction, prevention of initial contamination of the environment is the most important approach [2]. This can be achieved by taking several measures such as eliminat-ing patent infections in dogs and cats, preventing defeca-tion of pets in public areas, hygiene, and educating the public [6, 15, 16]. Methods to decrease contamination include: restriction of free-roaming dogs and cats, clean-ing up feces from soil and on pavements by dog owners, preventing access of dogs and cats to public places, es-pecially children’s playgrounds, and the use of strategic anthelminthic treatment of dogs and cats [1, 2, 4, 5]. Despite the proven association of household pet dogs and human toxocariasis, only a third (148/450) of veterinarian respondents routinely discussed the potential zoonotic hazards of canine roundworms with their clients and a large majority start anthelmintic on puppies after 4 weeks of age, when they already contaminate the environment [10, 17]. All dogs and cats should be screened for intesti-nal parasites, including ascarids, at least four times in the first year of life and at least twice every year in adults [2, 4]. Puppies and kittens should be given anthelmintic start-ing at 2 weeks of age and repeating every 2 weeks until regular broad-spectrum parasite control begins, and adult pets should receive year-round broad-spectrum parasite control with efficacy against ascarids [10].

REFERENCES1. Traversa D, Frangipane di Regalbono A, Di Cesare A, La Torre F, Drake J, Pietrobelli M: Environmental contami-nation by canine geohelminths. Parasites & vectors 2014, 7:67.2. Overgaauw PA, van Knapen F: Veterinary and public health aspects of Toxocara spp. Veterinary parasitology 2013, 193(4):398-403.3. Despommier D: Toxocariasis: clinical aspects, epide-miology, medical ecology, and molecular aspects. Clinical microbiology reviews 2003, 16(2):265-272.4. Palmer CS, Robertson ID, Traub RJ, Rees R, Thomp-son RC: Intestinal parasites of dogs and cats in Australia: the veterinarian’s perspective and pet owner awareness. Veterinary journal 2010, 183(3):358-361.5. Macpherson CN: The epidemiology and public health importance of toxocariasis: a zoonosis of global impor-tance. International journal for parasitology 2013, 43(12-13):999-1008.6. Glickman LT, Shofer FS: Zoonotic visceral and ocular larva migrans. The Veterinary clinics of North America Small animal practice 1987, 17(1):39-53.7. Glickman LT, Magnaval JF: Zoonotic roundworm infec-tions. Infectious disease clinics of North America 1993, 7(3):717-732.8. Stewart JM, Cubillan LD, Cunningham ET, Jr.: Prev-alence, clinical features, and causes of vision loss among patients with ocular toxocariasis. Retina 2005, 25(8):1005-1013.9. Petithory JC: [Visceral and cutaneous larva migrans]. La Revue du praticien 2007, 57(18):1977-1983.10. Lee AC, Schantz PM, Kazacos KR, Montgomery SP, Bowman DD: Epidemiologic and zoonotic aspects of as-carid infections in dogs and cats. Trends in parasitology 2010, 26(4):155-161.11. Fisher M: Toxocara cati: an underestimated zoonotic agent. Trends in parasitology 2003, 19(4):167-170.12. Singh A, Jr C, Stewart JM: Detection and Treatment Of Ocular Toxocariasis. Review of Ophthalmology 2007, 7.13. Singh BB, Sharma R, Gill JP: Toxocara canis, Trichi-nella spiralis and Taenia solium helminthozoonoses: se-roprevalence among selected populations in north India. Journal of parasitic diseases : official organ of the Indian Society for Parasitology 2015, 39(3):487-490.14. Parsons JC: Ascarid infections of cats and dogs. The Veterinary clinics of North America Small animal practice 1987, 17(6):1307-1339.15. Overgaauw PA, van Knapen F: [Negligible risk of vis-ceral or ocular larva migrans from petting a dog]. Neder-lands tijdschrift voor geneeskunde 2004, 148(32):1600-

1603.16. Aydenizoz-Ozkayhan M, Yagci BB, Erat S: The inves-tigation of Toxocara canis eggs in coats of different dog breeds as a potential transmission route in human toxo-cariasis. Veterinary parasitology 2008, 152(1-2):94-100.17. Harvey JB, Roberts JM, Schantz PM: Survey of vet-erinarians’ recommendations for treatment and control of intestinal parasites in dogs: public health implications. Journal of the American Veterinary Medical Association 1991, 199(6):702-707.