In your eyes

So how do you usually start your day?” This was a question I posed to a colleague in order to keep us from wallowing in possibilities regarding a good friend’s health situation. Being sensitive and astute, he gamely relayed waking up at 4 a.m. to attend to his furry pets, all seven which he affectionately calls “his boys.” This involves preparing their food and making sure that his Labrador gets a quick sprinkling to avoid having a funky smell. In past conversations, I have come to know how seriously he takes this responsibility, ensuring that they get their regular health checks, including dental appointments. On the very same day, we had a pediatric conference on a zoonotic disease that led me into writing on a topic that may be under the radar but is an equally important public health concern, and how we all can play a role in its prevention.

Have you heard about toxocariasis? As of this writing, the true burden of human disease is unknown, as most infections are either asymptomatic or subclinical, and diagnosis by serology comes at a cost. Based on available literature globally, a total of 1.4 billion people are estimated to be affected, with higher infection rates and exposure seen in tropical regions and developing countries.

What is toxocariasis? It is a zoonotic parasitic disease caused by the larvae of roundworms of dogs and cats known as Toxocara canis and Toxocara cati, respectively. Humans are accidental hosts and acquire the infection through the ingestion of embryonated eggs from soil, water, or surfaces contaminated with animal feces or from infected animal tissues.

To give an idea about the possibility of exposure locally, data from the Philippine Survey and Research Center Inc. showed that pet ownership was at 54 percent among the 1,000 households surveyed, with dogs as the most common pets followed by cats. Ownership was more common among higher socioeconomic classes and showed an increasing trend toward older age groups. According to the Philippine Animal Welfare Society report in 2019, the number of stray cats or dogs was estimated at 12 million. While rabies is a principal concern and rightly so, how many are aware of the consequences of Toxocara infection?

Infected individuals who manifest symptoms may present with nonspecific signs, such as fever, weight loss, itch, abdominal pain, rash, hepatomegaly, weakness, and dyspnea. Larvae can migrate through several organ systems, like the liver, lungs, tissues, and the central nervous system, with data showing that they can also affect the heart, gastrointestinal and genitourinary tracts, and the eyes. At our pediatric conference, the cases that were presented were children found to have ocular toxocariasis.

Ocular toxocariasis may affect adults but is mostly seen in older children. It usually involves only one eye and may present with blurring, painless loss of vision, photophobia, floaters, leukocoria, failing vision, and strabismus. According to our resource speaker, a retina specialist, it can also present as a red eye. In one of the three cases presented, ophthalmologic lesions resembled those of retinoblastoma.

Diagnosis rests on a high index of suspicion from the patient’s history (exposure), clinical manifestations, ophthalmologic and imaging findings, and is confirmed by serology. However, one has to take into consideration that serology has limitations, as it can cross-react with other parasitic infections and is not indicative of active or past disease.

Treatment for ocular toxocariasis involves the administration of steroids and albendazole. For complicated cases, surgery may be required. The key to avoiding the development of unfavorable and irreversible consequences lies in early recognition and treatment. Listening to the discussion got us thinking. Given the situation of having high pet ownership in our country and the presence of a considerable number of stray dogs and cats, which may harbor Toxocara species, how many cases remain undiagnosed? As clinicians, we had to ask ourselves if we may at one point have missed out on patients presenting with ocular symptoms. This was a wake-up call for all of us.

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Where to?

Our resource speaker, a highly respected and known figure in the field of parasitology and public health, offered plausible solutions to the problem. First and foremost, we should target the animal source and prevent environmental contamination, as “deworming humans cannot interrupt the life cycle of Toxocara species.” He called for responsible pet ownership, which includes regular deworming and health visits with the veterinarian, prompt and proper disposal of their pets’ waste, and close supervision, especially when around children. On a bigger scale, local government units should be responsible and accountable as the designated frontliners under the Anti-Rabies Act of 2007. While the law may be largely about rabies prevention, it includes measures which could tackle the problem of stray and unregistered dogs who may have missed out on being appropriately dewormed.

Needless to say, we need to act now before we lose sight of the situation.

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