Toxocara canis and Toxocara cati are nematode members of the family Ascarididae and known to cause toxocariasis in dogs and cats,1 as well as ocular toxocariasis in humans. Toxocara canis was first successfully recovered from a human eye in 19502 and has been recognized as a major cause of ocular toxocariasis in humans. We report a case in which T cati was possibly involved in the development of ocular toxocariasis.
A 38-year-old woman, with a history of keeping cats, complained of decreased visual acuity in her right eye. Corrected visual acuity was 20/200 OD. We found a yellowish, creamy lesion of two-thirds disc diameter in the inferior region of the macula. (Figure 1). Standard enzyme-linked immunosorbent assay (ELISA) using excretory–secretory products of second-stage larvae of T canis showed that antibody production was marginal. Despite this inconclusive result, we suspected ocular toxocariasis. If T cati was involved, antibody titer could be weak owing to an incomplete cross-reactivity between T canis and T cati. We conducted ELISA of the patient's serum samples using antigens of adult T cati, adult T canis, and second-stage larvae of T canis (Figure 2).
View of a fundus of the right eye showing mass formation caused by an allergic reaction to Toxocara cati.
Enzyme-linked immunosorbent assay of patient serum sample shows adult Toxocara cati, adult Toxocara canis, and second-stage larvae of T canis as simultaneous antigens. The results were inconclusive for patient 2 and showed the presence of T canis in patients 3 and 4.
In Figure 2, our case corresponds to patient 2, who showed an extraordinarily high antibody titer against adult T cati as compared with patients 3 and 4. Patients 3 and 4 were diagnosed as having ocular toxocariasis, shown by ELISA using T canis larvae and typical funduscopic features. The patient's several cats also provided evidence of ocular toxocariasis possibly caused by T cati. Though we had been unable to detect the presence of ova of T cati in the soil of cats, an unusually high titer of antibody against T cati prompted us to initiate therapy. Visual acuity in our patient returned to 20/20 OD following corticosteroid treatment.
Clinical diagnosis of ocular toxocariasis depends on serological testing,1 and ELISA has both high sensitivity and high specificity.3 Standard ELISA tests use the antigen prepared from T canis and show a high cross-reactivity between T canis and T cati,4 that is by no means incomplete. In this case, standard ELISA using T canis revealed that antibody titer was marginal. When using an antigen prepared from T cati, antibody titer was exceptionally high; consequently, we reached to a clinical diagnosis of ocular toxocariasis caused by T cati. Uga et al5 reported that cats are in closer contact to humans than dogs, underscoring the need to consider T cati in cases of ocular toxocariasis. Ophthalmologists should always be aware that ocular toxocariasis can be caused by T cati and consider conducting serological testing using T cati as a routine examination.
Corresponding author: Hidetoshi Kawashima, MD, Department of Ophthalmology, Jichi Medical School, Yakushiji, Minamikawachi, Kawachi-gun, Tochigi 329-0498, Japan (e-mail: email@example.com).
Sakai R, Kawashima H, Shibui H, Kamata K, Kambara C, Matsuoka H. Toxocara cati–Induced Ocular Toxocariasis. Arch Ophthalmol. 1998;116(12):1686-1687. doi: