Ocular parasitic diseases: a review on toxocariasis and diffuse unilateral subacute neuroretinitis

Recurrent vitreous opacity caused by intraocular Toxocara larva: a case report and literature review

BACKGROUND

Toxocara larva entity has seldom been reported on the surface of the retina. We report on an unusual case of recurrent vitreous opacity caused by intraocular Toxocara larva after vitrectomy.

CASE PRESENTATION

A 34-year-old male was referred to our clinic with a 6-month history of decreased visual acuity in the right eye characterized as red, painless, and progressive. Optos fundus photograph showed optic disc elevation with granuloma, and proliferative membrane starting from the optic disc and running towards the superior temporal retina due to the movement of a Toxocara larva, which was covered by the proliferative membrane in the superior temporal retina. Since it adhered closely to the retina, the lesion in the superior temporal retina was not removed to avoid induction of an iatrogenic retinal break and the larva was not found during the first diagnostic pars plana vitrectomy. Intraocular Anti-Toxocara IgG was 45.53U (< 3, enzyme-linked immunosorbent assay (ELISA)), and the Goldmann-Witmer coefficient was 8.55, confirming the diagnosis of ocular toxocariasis. After this operation, visual acuity improved to 20/200. However, vitreous opacity worsened again, and the proliferative membrane expanded around the Toxocara larva three weeks after the operation. Toxocara larva was found and removed in the superior temporal region during the second operation. His visual acuity improved to 20/100, vitreous opacity disappeared, and the retina was stable two months after the second operation.

CONCLUSION

It is advisable to remove suspected Toxocara larva to prevent the reoccurrence of ocular toxocariasis.

Frequency of Toxocara Antibodies in Patients Clinically Suspected to Ocular Toxocariasis, Northeast of Iran

Background:

Human toxocariasis is a neglected parasitic disease in most countries including Iran. Among different clinical forms of toxocariasis, ocular toxocariasis (OT) is an important disease resulting in severe vision loss. However, the prevalence and incidence of OT are currently unclear in Iran. This study aimed to determine the prevalence of ocular toxocariasis among patients with uveitis in the Northeast of Iran.

Methods:

From 2015 to 2017, 510 patients with uveitis referred to Khatam-al-Anbia, a tertiary eye hospital at Mashhad, Iran were examined for OT. Serum samples of the suspected patients were obtained and evaluated for IgG against Toxocara canis using ELISA test. Anti-Toxocara IgG positive serums were further investigated using confirmatory Western blotting (WB) analysis.

Results:

Twenty patients had pathologic changes and clinical presentations in the anterior and posterior segments of their eyes and they were clinically diagnosed ocular toxocariasis. Among the 20 patients, 2 (10%) patients showed IgG antibody against Toxocara canis on ELISA as well as on WB test. The calculated prevalence of ocular toxocariasis was about 0.4%.

Conclusion:

Ocular toxocariasis can be diagnosed both clinically and serologically in Mashhad, northeastern Iran. Although OT is a rare pathologic eye disease, it should be considered as one of the important cause of infectious posterior uveitis.

Short-term oral albendazole therapy for diffuse unilateral subacute neuroretinitis: A case report

Purpose

To report on a case of diffuse unilateral subacute neuroretinitis (DUSN) that was successfully treated with a short course of oral albendazole.

Observations

A 51-year-old male presented with severe visual loss secondary to DUSN associated with a positive Toxocara serology. Because the parasite could not be detected on fundoscopy, first-line treatment with photocoagulation could not be administered. Treatment with a 6-day course of oral albendazole resulted in the resolution of DUSN as well as the restoration of visual acuity.

Conclusion and importance

Although DUSN is characterized by the presence of a parasitic organism in the retina, there are cases in which the parasite is not visible. Albendazole has been used to treat such cases, but a standard treatment regimen has not been determined yet. Our case suggests that the resolution of DUSN can be achieved with short-term albendazole therapy.

Toxocara Awareness Among Medical Practitioners in Saudi Arabia

Human toxocariasis is a zoonotic infection with global and regional impacts. Worldwide it is underestimated and clinically overlooked. Medical practitioners are generally unaware of the extent of the resulting disease spectrum. The objective of the study was to assess knowledge and disease awareness among medical practitioners in Aseer, south-western Saudi Arabia. A questionnaire addressing knowledge about the parasite, its visceral larva migrans and the disease spectrum generated was used to interview participants. The study included 285 participants. In answer to the question what is toxocara, only 27%, answered correctly that it is a nematode, paediatricians being the majority. With regard to years of experience among participants, 56.8% of those who answered correctly had less than 5-year experience, as opposed to 35.4% for those with more than 10-year experience. The cumulative awareness about the disease manifestations and spectrum, i.e. those who knew, was less than 30% across specialties and years of experiences. Lack of awareness regarding Toxocara infection and the disease spectrum it can generate is evident. The consequence for such lack of knowledge within our practising medical community is simply unacceptable as it might translate into misdiagnosis and consequently misguided treatment.

Diffuse unilateral subacute neuroretinitis: review article

Diffuse unilateral subacute neuroretinitis (DUSN) is an ocular infectious disease that can lead to severe visual impairment and blindness. It usually occurs in healthy young individuals and depending on the stage of the disease, it may present as vitritis, multifocal gray-white lesions in the outer retina, and derangement of the retinal pigment epithelium, narrowing of the retinal vessels and optic atrophy. Parasites of different sizes and species have been proposed as the etiologic agent of DUSN, including Ancylostoma caninum, Toxocara canis, and others. Thus, it is hypothesized that different infectious worms may be considered as the likely cause of both an autoimmune and toxic form of nematode retinopathy. Because serologic testing is variable, the definitive diagnosis is made when clinical characteristics of DUSN are found in conjunction with an intraocular worm. Ancillary tests can assist in the differential diagnosis when the nematode cannot be visualized, such as fluorescein and indocyanine green angiography, electrophysiological tests, visual field studies, and more recently, optical coherence tomography angiography. Cases in which the worm can be identified, it is defined as confirmed DUSN, and eyes with the typical clinical features but without identification of the worm should be classified as presumed DUSN. In confirmed DUSN, the classic treatment is directly photocoagulation of the worm; however, it can only be visualized in 30% (to 40%) of cases. Treatment of presumed DUSN cases with high-dose oral albendazole has shown encouraging results. However, perhaps due to the disease’s rarity or its underdiagnosis, there are no studies comparing current treatment modalities in both presumed and confirmed DUSN. Due to the possibility of this disease being, in part, autoimmune nematode retinopathy, corticosteroids associated with both albendazole or laser therapy, could be in any way beneficial. Thus, further comparative studies are necessary to elucidate the best treatment for this potentially blinding disease.

New insight into the diagnostic cut-off value of serum anti-Toxocara IgG for ocular toxocariasis in uveitis patients

Uveitis is one of the commonest causes of vision loss worldwide and its exact etiology is still not clarified in most patients. The current study is a trial to assess the efficacy of serum anti-Toxocara immunoglobulin G (IgG) by enzyme-linked immunosorbent assay (ELISA) as a diagnostic tool for ocular toxocariasis (OT) and to detect OT prevalence and the associated ocular manifestations in sera of patients with uveitis. One hundred and twelve patients (62 females and 50 males) with uveitis were diagnosed by ophthalmologists, radiologists and rheumatologists according to ocular manifestations, laboratory and radiological investigations. Serum anti-Toxocara IgG titers were determined by ELISA in sera of all patients. Our results revealed that OT is highly associated with intermediate and posterior uveitis. Children and young adult females, especially those residing in rural areas, complained mainly of diminution of vision in the left eye, with strabismus and leukocoria. At a cut-off value of 0.258, the sensitivity and specificity of IgG ELISA were 93.3% and 100%, respectively. In conclusion, at a novel cut-off value of 0.258 the serum anti-Toxocara IgG ELISA is predicted to be a diagnostic tool for OT regarding sensitivity and specificity. Also, it has potential importance in the interpretation and differential diagnosis of OT. Thus, serum anti-Toxocara IgG ELISA should be a routine test for screening of suspected cases.

Toxocara Neuroretinitis Associated with Raw Meat Consumption

Neuroretinitis characterized by optic disc edema and star-like exudates in the macula was detected in a patient who presented with sudden unilateral painless vision loss and had a history of raw meat consumption. The patient tested seropositive for Toxocara. Combination therapy with steroid and albendazole resulted in an increase in visual acuity and complete resolution of clinical signs.

Baylisascaris procyonis Roundworm Seroprevalence among Wildlife Rehabilitators, United States and Canada, 2012-2015

Baylisascaris procyonis roundworms can cause potentially fatal neural larva migrans in many species, including humans. However, the clinical spectrum of baylisascariasis is not completely understood. We tested 347 asymptomatic adult wildlife rehabilitators for B. procyonis antibodies; 24 were positive, suggesting that subclinical baylisascariasis is occurring among this population.

Prevalence of Baylisascaris in domestic dog coprological examinations in the United States, 2013-2016

Dogs are alternative definitive hosts for Baylisascaris procyonis, the raccoon roundworm, but broad-scale prevalence and distribution of canine cases is not known. Based on a large dataset from nationwide reference laboratories, Baylisascaris spp. eggs were detected in 504/9,487,672 (0.005%) canine fecal samples. While many of the positive dog samples originated in areas of known high B. procyonis prevalence in raccoons, positives were also detected in 9 new states. Young dogs, large breeds, and certain regions had higher prevalence. Although overall prevalence was low, and some infections may be spurious, these results demonstrate that dogs may shed Baylisascaris spp. into domestic environments. Routine parasitic testing, rigorous preventive use, and restrictions on coprophagy should be encouraged to reduce risk of human or animal exposure to infectious eggs.

Cerebral Toxocariasis: Silent Progression to Neurodegenerative Disorders?

Toxocara canis and T. cati are highly prevalent nematode infections of the intestines of dogs and cats. In paratenic hosts, larvae do not mature in the intestine but instead migrate through the somatic tissues and organs of the body. The presence of these migrating larvae can contribute to pathology. Toxocara larvae can invade the brains of humans, and while case descriptions of cerebral toxocariasis are historically rare, improved diagnosis and greater awareness have contributed to increased detection. Despite this, cerebral or neurological toxocariasis (NT) remains a poorly understood phenomenon. Furthermore, our understanding of cognitive deficits due to toxocariasis in human populations remains particularly deficient. Recent data describe an enhanced expression of biomarkers associated with brain injury, such as GFAP, AβPP, transforming growth factor β1 (TGF-β1), NF-L, S100B, tTG, and p-tau, in mice receiving even low doses of Toxocara ova. Finally, this review outlines a hypothesis to explore the relationship between the presence of T. canis larvae in the brain and the progression of Alzheimer's disease (AD) due to enhanced AD-associated neurodegenerative biomarker expression.

Clinical experience in treatment of diffuse unilateral subretinal neuroretinitis

Purpose

To describe the clinical features, management, and outcomes of patients with diffuse unilateral subacute neuroretinitis (DUSN).

Methods

A noncomparative, consecutive analysis of case series from two tertiary care campuses of LV Prasad Eye Institute, India, between January 2011 and April 2014 was performed. Medical records of the patients presenting with DUSN (early or late stage) were reviewed.

Results

The current study included 13 patients. The majority (10/13, 76.92%) of the patients were aged 20 years or less. All patients had unilateral eye involvement. Visual acuity at presentation was 20/200 or worse in 9/13 (69.23%) patients. A delay in diagnosis occurred in 6/13 patients, and initial diagnosis in these patients included retinitis pigmentosa (4 patients) and posterior uveitis (2 patients). Clinical features included early presentation (prominent vitritis, localized retinitis, and vasculitis) in 7/13 (53.85%) patients and late presentation (attenuation of vessels, retinal pigment epithelium atrophic changes, and optic atrophy) in 6/13 (46.15%) patients. Worm could not be identified in any of the cases. All the patients received laser photocoagulation of retina and oral albendazole treatment for a period of 30 days. With treatment, visual acuity improved in seven patients (six early stage, one late stage) and remained unchanged in six patients. Mean follow-up period was 8.69 months (range, 1–21 months). The mean central foveal thickness in the affected eye, done by optical coherence tomography, during the late stage of the disease was 188.20±40 µm (range, 111–242 µm), which was significantly thinner than the fellow eye, 238.70±36.90 µm (range, 186–319 µm), P=0.008.

Conclusion

DUSN is a serious vision threatening disease, which may progress to profound vision loss in the later stage of the disease. Visualization of subretinal worm is usually not possible. Treatment with high-dose albendazole therapy and laser photocoagulation may alter the blood–retinal barrier and may be useful in achieving visual recovery.

Diffuse unilateral subacute neuroretinitis in a healthy Korean male: the first case report in Korea

A 52-yr-old male was referred for progressive visual loss in the left eye. The decimal best-corrected visual acuity (BCVA) was 0.01. Fundus examination revealed diffuse retinal pigment epithelial degeneration, focal yellow-white, infiltrative subretinal lesion with fuzzy border and a live nematode within the retina. Diffuse unilateral subacute neuroretinitis (DUSN) was diagnosed and the direct laser photocoagulation was performed to destroy the live nematode. During eight months after treatment, BCVA gradually improved to 0.2 along with the gradual restoration of outer retinal layers on SD-OCT. We report on the first case of DUSN in Korea. DUSN should be included in the differential diagnosis of unexplained unilateral visual loss in otherwise healthy subjects.

Toxocariasis: A Review for Pediatricians

Toxocariasis is a parasitic disease caused by roundworms of cats and dogs. The disease is endemic throughout the United States and causes significant morbidity in children, including damage to the lungs, liver, or central nervous system, especially the eyes. Two well established clinical syndromes of disease include visceral and ocular toxocariasis. Symptoms of visceral toxocariasis include abdominal pain, cough, or wheezing. Vision loss or strabismus are common symptoms of ocular toxocariasis. Serologic testing for presence of Toxocara antibody is available, although a positive test result does not necessarily correlate with active clinical infection. Albendazole or mebendazole is the recommended treatment for visceral toxocariasis. Treatment options for ocular toxocariasis include corticosteroids or ophthalmic surgery; anthelminthic medications also may be used. Risk for toxocariasis can be reduced by handwashing after soil contact, routine pets deworming, discouraging geophagia, and appropriate disposal of pet feces.

Therapeutic battle against larval toxocariasis: are we still far behind?

Toxocariasis is a widespread zoonotic helminthic disease. Human infection is acquired by ingestion of embryonated eggs of Toxocara which reach the environment via stools of dogs and cats. In paratenic hosts, such as humans and mice, the hatched larvae migrate systematically in the body and could reach critical sites such as the eye and the central nervous system. The clinical expression of toxocariasis includes two main forms of varying intensity: visceral and ocular, as well as several organ-specific clinical manifestations. The issue of treatment is a matter of great controversy not only because of limited efficacy of anthelmintic drugs in terms of parasite eradication, but also because of doubts about the benefits of therapy as most Toxocara infections are self-limiting. Many animal studies were conducted employing different drugs and regimens, yet the results were variable and inconsistent. On the other hand, experience in human therapy is unfortunately limited due to paucity of clinical trials. Herein, the problems and pitfalls of treatment of toxocariasis are addressed, and new trends in therapy are discussed.

Ocular toxocariasis: epidemiologic, anatomic, and therapeutic variations based on a survey of ophthalmic subspecialists

PURPOSE

To assess the current burden of ocular toxocariasis (OT) and to gain knowledge regarding the diagnostic and treatment practices used in the ophthalmologic community in the United States.

DESIGN

Web-based, cross-sectional survey.

PARTICIPANTS

Subspecialty ophthalmologists who are currently practicing in the United States.

METHODS

An electronic survey was sent to 3020 ophthalmologic subspecialists belonging to the American Uveitis Society (AUS), the American Society of Retina Specialists (ASRS), or the American Association for Pediatric Ophthalmology and Strabismus (AAPOS) to capture demographic, clinical, diagnostic, and treatment data on patients with OT seen in their practices between September 2009 and September 2010.

MAIN OUTCOME MEASURES

The demographic, epidemiologic, and clinical characteristics of each reported patient with OT.

RESULTS

A total of 159 patients with OT were reported by 559 respondents (19%). The median patient age was 11.5 years (range, 1-66 years). Seventy-two patients (45%) with OT lived in the Southern region of the United States. Thirty-one (69%) of 45 patients with OT owned a dog or cat. Vision loss was reported in 46 (85%) of 54 patients with OT; 32 (71%) of 45 patients had permanent vision loss, 13 patients (29%) had temporary vision loss, and duration of vision loss was unreported for 1 patient. Of the 32 patients with OT with permanent vision loss, 30 (94%) had a subretinal granulomatous mass/scar, peripheral granuloma with traction bands, or posterior pole granuloma noted on ophthalmologic examination. Subretinal granulomatous mass/scar, vitritis, and scotoma were the most common ophthalmologic signs found on examination of patients with OT.

CONCLUSIONS

Ocular toxocariasis continues to occur in the United States, where it affects mainly children and causes permanent vision loss in many patients. Healthcare professionals should counsel patients and their family members about prevention strategies in an effort to decrease infection rates and morbidity due to Toxocara. Further improvement of diagnostic and treatment tools is needed to assist ophthalmologists in treating patients with OT.

FINANCIAL DISCLOSURE(S)

The author(s) have no proprietary or commercial interest in any materials discussed in this article.

Zoonotic helminths affecting the human eye

Nowaday, zoonoses are an important cause of human parasitic diseases worldwide and a major threat to the socio-economic development, mainly in developing countries. Importantly, zoonotic helminths that affect human eyes (HIE) may cause blindness with severe socio-economic consequences to human communities. These infections include nematodes, cestodes and trematodes, which may be transmitted by vectors (dirofilariasis, onchocerciasis, thelaziasis), food consumption (sparganosis, trichinellosis) and those acquired indirectly from the environment (ascariasis, echinococcosis, fascioliasis). Adult and/or larval stages of HIE may localize into human ocular tissues externally (i.e., lachrymal glands, eyelids, conjunctival sacs) or into the ocular globe (i.e., intravitreous retina, anterior and or posterior chamber) causing symptoms due to the parasitic localization in the eyes or to the immune reaction they elicit in the host. Unfortunately, data on HIE are scant and mostly limited to case reports from different countries. The biology and epidemiology of the most frequently reported HIE are discussed as well as clinical description of the diseases, diagnostic considerations and video clips on their presentation and surgical treatment.