Ocular Filariasis in Human Caused by Breinlia (Johnstonema) annulipapillata Nematode, Australia

We report a human case of ocular filariasis, caused by a species of Breinlia nematode, from Queensland, Australia. Morphological and molecular evidence indicated that the nematode Breinlia (Johnstonema) annulipapillata, or a closely related taxon, likely transmitted from a macropodid marsupial host was involved, which might represent an accidental finding or an emerging zoonosis.

The sequences obtained were aligned to those accessible publicly for 34 (SSU) or 29 (cox-1) species of filarioid and of Mastophorus muris (outgroup) ( Figure  2). Aligned SSU and cox-1 sequence data were subjected to separate phylogenetic analyses using the Bayesian inference method (8), with nodal support values given as posterior probabilities. The resultant trees ( Figure 2) revealed that the nematode under study is a member of the genus Breinlia, as it grouped with Breinlia from the opossum, B. mundayi (SSU only), and B. jittapalapongi with strong statistical support. Thus, this worm could be identified molecularly as a Breinlia sp.; it could not be identified to species because of the lack of sequence data for Breinlia spp. in public databases.
There are 5 reports of human intraocular filariasis from Australia: 4 suspected D. immitis cases from New South Wales, Queensland, and Victoria (9-12); and 1 Dipetalonema (Acanthocheilonema) reconditum case from Victoria (13). The short, heavily sclerotized spicules of this specimen, with a bifid distal extremity on the right spicule ( Figure 1), indicated that it was neither of these taxa, but rather B. (J.) annulipapillata. This species occurs in a range of macropodid species, predominantly in northern Australia, although it is also found in swamp wallabies in the south.   larger, heavily sclerotized spicules, but without a bifid extremity on the right spicule, and occurs in the short-eared rock wallaby (Petrogale brachyotis) in the Northern Territory (14).
Although no life cycles of subgenus Johnstonema nematodes are known, those of 4 species of the subgenus Breinlia are known and involve Aedes mosquitoes as intermediate hosts (14). The patient was probably been bitten by the intermediate host of this filarioid, possibly a mosquito, that had previously taken a blood meal from a macropodid and was carrying infective larval stages (L3s). Once in the patient, the L3s would have undergone 2 additional molts and established themselves in the eye and perhaps in other tissues throughout the body (although there was no evidence of infection elsewhere). Adult Breinlia nematodes are found predominantly in the peritoneal and pleural cavities of mammalian definitive hosts (14). However, other filarial nematodes have a tropism for the eye, and several cases have been reported of zoonotic filariasis of the eye relating to Dirofilaria sp. nematodes (1). Breinlia nematodes had not been found previously in humans, but B. sergenti nematodes has been recorded in the slow loris (Nycticebus coucang) in Southeast Asia (14). It is possible that ocular Breinlia infections may go undetected in humans, particularly in less conspicuous places than the eye, and may be more common than expected in areas where Breinlia-infected marsupials are prevalent.

Conclusions
This human case of ocular filariasis caused by Breinlia sp. nematodes is highly unusual and was likely transmitted from a kangaroo or wallaby via a bloodfeeding intermediate host, possibly a mosquito, to the patient. Microscopic identification of filarioids can be challenging, depending on their stage of development and sex, but fortuitously that was not the case here. Nevertheless, the use of the current molecular approach can be advantageous for generic or specific identification, provided that sufficient sequence data are available in public databases. We recommend that both morphological and molecular tools be used to attempt to achieve a specific diagnosis in cases of human ocular filariasis.
This study was partially supported through a grant from the Australian Research Council (grant no. LP160101299 to R.B.G. and A.V.K.).

About the Author
Dr. Koehler is a molecular parasitologist in the Gasser Lab in the Department of Veterinary Biosciences at The University of Melbourne, Australia. His research interests include the phylogenetics and biology of parasites.