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Diagnosis

Diagnosis of either visceral toxocariasis or ocular toxocariasis are based on the presence of signs of VT or OT and history of exposure to a potential source of infectious Toxocara eggs or larvae (e.g. in undercooked infected meat or offal). The diagnosis of visceral toxocariasis is based on compatible disease and exposure history with positive results by serological testing. The currently recommended test is an enzyme-linked immunosorbent assay (ELISA) with larval stage antigens, usually excretory/secretory antigens are released when infective Toxocara larvae are cultured. The specificity of this assay is good although cross reactivity with antibody to the human roundworm, Ascaris lumbricoides, is possible; however, assays employing Toxocara excretory/secretory antigens minimize this problem. Positive serological results should be interpreted with consideration of the patient’s clinical status. Detectable antibody may be the result of infection in the past. Also, seropositivity can be present in asymptomatic Toxocara infection. Paired serum samples demonstrating a significant rise in antibody level over time may be useful to confirm active infection.

In ocular toxocariasis, Toxocara antibody levels in serum can be low or absent despite clinical disease. In some cases, Toxocara antibody can be detected in the aqueous or vitreous fluid samples from the affected eye and may be due to local antibody production or leakage of antibody from the circulation. The ocular fluid sample may be tested at a lower dilution than serum to improve ELISA sensitivity.

Signs and symptoms of VT or OT can be caused by the migrating larvae of other helminths, including Baylisascaris procyonis (both VT and OT), Strongyloides spp. (VT), and Paragonimus spp. (VT). Careful attention to disease course, exposure history and serological testing can be useful for differential diagnosis. For OT, if a larva is visualized in the eye, measuring size may help differentiate the larger larvae of Baylisascaris from Toxocara or other larvae.

Disease

The manifestations of toxocariasis reflect the number of migrating larvae, where the larvae have migrated in the body, and the degree of immune response and inflammation that developed in response to the presence of the larvae. Many infections are asymptomatic. In heavy infections, large numbers of larvae may migrate through liver and lungs or other internal organs, causing inflammation and symptomatic disease (VT). Rarely, larvae may migrate to the central nervous system (CNS) causing eosinophilic meningoencephalitis or granuloma formation in the CNS. Signs of VT include fever, cough, wheezing, abdominal pain, and hepatomegaly. Eosinophilia is often present. Visceral toxocariasis has been proposed as a cause of asthma; however, there may be multifactorial causes of asthma and further study is needed to establish a causative link between toxocariasis and asthma.

Typically, OT is a unilateral disease, when a larva penetrates a single eye. Common signs are associated with granulomatous inflammation especially in the retina, uveitis, and/or chorioretinitis. Patients can present with leukocoria and decreased vision in the affected eye which may be confused with retinoblastoma. Diffuse unilateral subacute neuroretinitis or vitreal bands may develop.

Treatment

Treatment with albendazole or mebendazole is indicated for visceral toxocariasis, although optimal duration of treatment is undefined. Both drugs are metabolized in the liver; prolonged use of albendazole (weeks to months) has led to development of pancytopenia in some patients with compromised liver function. Patients on long term treatment should be monitored by serial blood cell counts. However, albendazole has been used to treat millions of patients worldwide and in mass drug administration campaigns, and it is considered to be a safe drug with low toxicity record. In addition to antiparasitic therapy, symptomatic therapy including steroid treatment to control inflammation may be indicated.

Drug	Dose and duration
Albendazole	400 mg by mouth twice a day for five days (both adult and pediatric dosage)
Mebendazole	100-200 mg by mouth twice a day for five days (both adult and pediatric dosage)

Oral albendazole is available for human use in the United States.

Oral mebendazole is available for human use in the United States.

For ocular toxocariasis, the goal of treatment is to minimize damage to the eye. Systemic antiparasitic treatment with albendazole or mebendazole at the same doses as for visceral disease may be beneficial for active disease. Attempts to surgically remove the larva may be unsuccessful. Control of inflammation in the eye by use of topical or systemic steroids may be indicated. For patients with quiescent disease, improved outcomes may result from surgical intervention to prevent further damage due to chronic inflammation.

Albendazole

Albendazole is pregnancy category C. Data on the use of albendazole in pregnant women are limited, though the available evidence suggests no difference in congenital abnormalities in the children of women who were accidentally treated with albendazole during mass prevention campaigns compared with those who were not. In mass prevention campaigns for which the World Health Organization (WHO) has determined that the benefit of treatment outweighs the risk, WHO allows use of albendazole in the 2nd and 3rd trimesters of pregnancy. However, the risk of treatment in pregnant women who are known to have an infection needs to be balanced with the risk of disease progression in the absence of treatment.

Pregnancy Category C: Either studies in animals have revealed adverse effects on the fetus (teratogenic or embryocidal, or other) and there are no controlled studies in women or studies in women and animals are not available. Drugs should be given only if the potential benefit justifies the potential risk to the fetus.

It is not known whether albendazole is excreted in human milk. Albendazole should be used with caution in breastfeeding women.

The safety of albendazole in children less than 6 years old is not certain. Studies of the use of albendazole in children as young as one year old suggest that its use is safe. According to WHO guidelines for mass prevention campaigns, albendazole can be used in children as young as 1 year old. Many children less than 6 years old have been treated in these campaigns with albendazole, albeit at a reduced dose.

Mebendazole

Mebendazole is in pregnancy category C. Data on the use of mebendazole in pregnant women are limited. The available evidence suggests no difference in congenital anomalies in the children of women who were treated with mebendazole during mass treatment programs compared with those who were not. In mass treatment programs for which the World Health Organization (WHO) has determined that the benefit of treatment outweighs the risk, WHO allows use of mebendazole in the 2nd and 3rd trimesters of pregnancy. The risk of treatment in pregnant women who are known to have an infection needs to be balanced with the risk of disease progression in the absence of treatment.

It is not known whether mebendazole is excreted in breast milk. The WHO classifies mebendazole as compatible with breastfeeding and allows the use of mebendazole in lactating women.

The safety of mebendazole in children has not been established. There is limited data in children age 2 years and younger. Mebendazole is listed as an intestinal antihelminthic medicine on the WHO Model List of Essential Medicines for Children, intended for the use of children up to 12 years of age.

Page last reviewed: May 26, 2020

Content source: Global Health, Division of Parasitic Diseases and Malaria