What are the other Names for this Condition? (Also known as/Synonyms)
- Ocular Toxocariasis
- OLM (Ocular Larva Migrans)
What is Ocular Larva Migrans? (Definition/Background Information)
- Ocular Larva Migrans (OLM) is a type of toxocariasis, which is a parasitic roundworm infection. In OLM, the larvae of the infecting parasite migrate to the eyes and optic nerve, causing characteristic eye-related symptoms
- Toxocariasis is transmitted from animals (commonly cats and dogs) to humans, making it a zoonotic infection. The infection occurs when a human ingests the parasite
- This mostly occurs via contamination of one’s hands or food (prior to eating) with the feces of an infected animal. The infection can occur from ingestion of undercooked or raw meat/poultry that is infected
- The symptoms of Ocular Larva Migrans include swollen eyes and vision abnormalities. If left untreated, the individual can lose vision in the affected eye. Additionally, there is a likelihood of secondary ocular infections, or the condition being misdiagnosed as retinoblastoma (a malignant eye tumor)
- The treatment of Ocular Larva Migrans infection is aimed at limiting damage to the eyes and restoring one’s vision. The treatment measures may include steroids (topical or injected), anti-parasitic medication, and surgery (if required). With early detection and prompt treatment, it may be possible to clear the infection and save the infected eye
Who gets Ocular Larva Migrans? (Age and Sex Distribution)
- Ocular Larva Migrans is reported globally, although it is predominantly diagnosed in individuals living in poverty and poor economic status
- The infection occurs more commonly in teenagers and adults
- No gender bias is noted and both males and females are affected
What are the Risk Factors for Ocular Larva Migrans? (Predisposing Factors)
The following factors may increase one’s risk of being infected by Ocular Larva Migrans:
- Having a cat or dog, especially puppies and kittens: Young animals have a weaker immune system and decreased ability to fight infections and foreign pathogens. Toxocara can also be passed through milk from a lactating dog or cat to its offspring
- Owning a household pet that has not been treated for worms
- Breeding animals inside the house/household
- Young children who play outdoors: Children may come into contact with animal feces or soil contaminated by animal feces, which may then infect them via the oral route (mouth). Toys dropped to the ground may be inadvertently placed in the mouth
- Ingesting raw or undercooked meat infected with larvae of Toxocara
It is important to note that having a risk factor does not mean that one will get the condition. A risk factor increases one’s chances of getting a condition compared to an individual without the risk factors. Some risk factors are more important than others.
Also, not having a risk factor does not mean that an individual will not get the condition. It is always important to discuss the effect of risk factors with your healthcare provider.
What are the Causes of Ocular Larva Migrans? (Etiology)
Ocular Larva Migrans (OLM) is caused by the parasitic roundworm belonging to the genus Toxocara. OLM is a type of infection known as Toxocariasis.
- Eggs of Toxocara species are often found in animal feces, or soil that has been contaminated by animal feces
- However, it may take between 2-4 weeks under ideal conditions (such as temperature and humidity) to become infective
- When Toxocara eggs containing embryos are ingested and enter the human gut, they hatch. The released larvae then infect the intestinal wall
- The larvae live inside the host, feeding-off the host cells by digesting them
- The larvae/worm can also move from one site to another within the human body via the bloodstream, causing inflammatory reactions at each site, resulting in symptoms
- When Toxocara has traveled or migrated to the eye of the host, it causes lesions in the eye. Typically, only one eye is infected
What are the Signs and Symptoms of Ocular Larva Migrans?
The severity of symptoms of Ocular Larva Migrans may vary among the affected individuals. The signs and symptoms may include:
- Low-grade fever
- Eosinophilia: Elevated eosinophils in blood, indicative of a parasitic infestation
- White spots in the eye (or granulomas, often misdiagnosed as retinoblastoma)
- Swelling or inflammation of the eye
- Vision changes and vision loss
How is Ocular Larva Migrans Diagnosed?
A diagnosis of Ocular Larva Migrans (OLM) is made by the following tests and exams:
- A thorough physical examination and complete medical history investigation
- Dilated eye exams
- Blood test for measuring the level of eosinophils
- Confirmation of the presence of parasitic infection in the serum/intra-ocular fluids/cerebrospinal fluid, through antibody detection using enzyme-linked immunosorbent assay (ELISA)
- Differential diagnosis for OLM: Ruling out other eye conditions that may present with similar symptoms. One such example is retinoblastoma, and imaging techniques, such as optical coherence tomography or B-scan ultrasonography, may be helpful for a differential diagnosis
Many clinical conditions may have similar signs and symptoms. Your healthcare provider may perform additional tests to rule out other clinical conditions to arrive at a definitive diagnosis.
What are the possible Complications of Ocular Larva Migrans?
Ocular Larva Migrans may lead to the following complications:
- Vision impairment due to tractional and retinal detachment
- Complete loss of vision
- Removal of the affected eye - that may be warranted due to excessive damage of the eye, or from misdiagnosis of the condition as retinoblastoma
How is Ocular Larva Migrans Treated?
Ocular Larva Migrans is typically difficult to treat. The methods adopted are meant to address deterioration of vision and prevent further damage to the affected eye. These may include:
- Topical steroids to reduce eye inflammation
- In severe cases, administration of steroid injections in the periocular space (the area surrounding the eyeball)
- Use of prescription anti-parasitic medication has found limited success. The medicine of choice is albendazole
- Vitrectomy: It is the surgical removal of the vitreous gel from the middle of the eye. This surgery is performed to correct retinal detachment and improve vision
How can Ocular Larva Migrans be Prevented?
Ocular Larva Migrans may be achieved by adhering to the following practices:
- Washing hands, especially after being outdoors, gardening, or handling animals or playing with pets, prior to eating or performing other related activities
- Frequently deworming household animals including cats and dogs
- Having thoroughly cooking food (especially meat)
- Clearing/disposing pet feces in a timely and appropriate manner
- Supervising young children while they play outdoors; ensuring that children avoid the ingestion of soil or dirt
What is the Prognosis of Ocular Larva Migrans? (Outcomes/Resolutions)
- The prognosis of Ocular Larva Migrans is determined by the severity of infection, and if any complications have developed
- Mild infections may be treatable using steroidal and anti-parasitic medications. Severe infections with complications may result in loss of vision in the affected eye
Additional and Relevant Useful Information for Ocular Larva Migrans:
The life cycle of Toxocara is as follows:
- The parasite eggs are passed through the feces of an infected animal
- The eggs become embryonated in the environment (outside the animal), if conditions, such as humidity and temperature, are ideal
- Once embryonated, the eggs are infective, and hatch once ingested by an animal or human
- The larvae infect the intestinal wall in the small intestine
- The roundworm develops into an adult, once it infects the small intestine and is able to lay eggs that are passed through the feces
- The cycle repeats when eggs are ingested by another animal or host
Humans are paratenic hosts i.e., hosts who are not necessary for the parasite to complete its life cycle. However, such hosts may still contribute towards maintaining the life cycle of the parasite.