Ocular dirofilariasis: Ophthalmic implication of climate change on vector-borne parasites.

PURPOSE: To describe a geographically rare case of ophthalmic dirofilariasis. OBSERVATIONS: An 81-year-old male of good socioeconomic status living in the state of Michigan in the United States, presented to the eye clinic with a painful red left eye. He had not traveled outside of the state of Michigan in over three years. He was found to have a 7 cm long subconjunctival roundworm, which was ultimately extracted. CONCLUSIONS AND IMPORTANCE: With increasing global temperatures, ocular dirofilariasis is being introduced in more northern climates and should be included in the differential diagnosis in areas previously isolated from these vector-borne parasites.

Introduction

This is a rare case of ophthalmic dirofilariasis in an 81-year-old man with sudden pain in the left eye. The nematode was located subconjunctivally and recognized as dirofilariasis. This case occurred in an unusual geographic location, in Michigan, U.S.A, which ultimately may be due to global climatic changes toward warmer temperatures.

Case report

An 81-year-old male of good socioeconomic status living in the state of Michigan in the United States, presented to the eye clinic with a painful red left eye in the month of April. Consent to publish was obtained in writing and orally. He had not traveled outside of the state of Michigan in over three years and denied exposure to heavily wooded areas, swampland, or other nature reserves. His left eye had been feeling irritated, and he awoke the morning of presentation with significant tenderness to touch in the superonasal quadrant of the eye. On examination, he had diffuse subconjunctival injection with a mobile, elevated subconjunctival mass superonasally (Fig. 1). The lesion was explored by slit lamp, and a three-inch roundworm was extracted using jeweler forceps, later determined to be Dirofilaria (Fig. 2).

Fig. 1

External photograph of subconjunctival dirofilariasis in the left eye prior to extraction.

Fig. 2

Photograph of Dirofilaria roundworm of roughly 7 cm in length following subconjunctival removal.

Discussion

Commonly known as the dog heartworm, Dirofilaria is a genus of nematodes, or roundworms, endemic to Mediterranean countries. The life cycle of Dirofilaria species relies on a vector, commonly mosquitos, for the “Larvae 3” or L3 stage, as well as a definitive vertebrate hosts, typically canine and feline species. Humans can rarely become hosts, predominantly with pulmonary and cardiac involvement, however ocular dirofilariasis has been reported subconjunctivally, intravitreally, and intraorbitally with the two notable species Dirofilaria immitis and Dirofilaria repens. In recent years, incident rates of animal infections have increased. Although most Dirofilaria infections worldwide occur in tropic and subtropical locations, our unique case shows a trend of migration towards more northern areas typically devoid of such vector-borne parasites. The temperature in Michigan has risen nearly 2° Fahrenheit since 1980 and the northern hemisphere was likely the warmest 30-year period of the last 1400 years, which may allow more incubation time for the L3 stage that develops only at temperatures above 57 °F for a long enough duration for infectious maturity.2, 3, 4 With temperatures continuing to rise globally, including in the northern United States, there may possibly be an increase in incidence of ophthalmic parasitic infections typically reserved for more tropical environments.

Conclusions

With increasing global temperatures, ocular dirofilariasis will have longer incubation time for infectious maturation and may possibly be introduced in more northern climates previously isolated from these vector-borne parasites.

Patient consent

The patient consented to publication of the case in writing and orally.

Financial disclosures

The authors have no proprietary or commercial interest in any materials discussed in this article.

Acknowledgements and disclosures

Funding

No funding or grant support.

Conflicts of interest

The following authors have no financial disclosures: JB, GS, AT.

Authorship

All authors attest that they meet the current ICMJE criteria for Authorship.