Diagnosis of Ocular Loiasis in a Patient from a Dirofilaria-Endemic Area

A 49-year-old man visited our hospital to confirm filarial infection. He had a history of subconjunctival worm extraction in Dubai, where the peripheral blood smear was positive for microfilaria. He was then referred for treatment in his hometown (Kerala, India). He had no systemic or visual symptoms. He had worked in Nigeria for three years before moving to Dubai. Histopathological sections and peripheral blood smears were analyzed. Longitudinal sections of the extracted adult worm showed a rounded anterior end with no lips (Figure 1A) and the uterus filled with embryonic microfilariae (Figure 1B). Blood smears revealed sheathed microfilariae, with nuclei extending to the pointed tail tip (Figure 1C, 1D). The adult worm was identified as a female Loa loa worm. He received systemic therapy with corticosteroids and diethylcarbamazine.

FIGURE 1:
Longitudinal sections of the adult worm showing a rounded anterior end with no lips (A) and the uterus filled with embryonic microfilariae (B). The exterior region of the cuticle lacks ridging as seen inDirofilaria repens. Giemsa-stained microfilaria ofLoa loain a thin blood smear showing a cephalic space (C) and nuclei extending to the pointed tip of the tail (D).

Dirofilaria repens and Brugia malayi infections are endemic to Kerala¹. Subconjunctival dirofilariasis is very common in Kerala and needs differentiation from loiasis, which has a similar presentation^1,2. Our patient most likely acquired the infection in Nigeria, where Loa loa is endemic³. The adult worm of D. repens can be differentiated from Loa loa based on longitudinal ridges on the cuticle and that it is rarely detected in the gravid state². Except for a few cases, microfilaremia has not been reported in human dirofilariasis¹. The sheathed microfilaria of B. malayi has a hot-pink sheath (Giemsa stain) and two terminal nuclei in the blunt tail tip, whereas Loa loa has a colorless sheath (Giemsa stain), dense nuclear column, and nuclei extending to the pointed tip². However, the microfilaria of Dirofilaria spp. and Loa loa is quite similar². Correct identification can help in deciding the appropriate treatment modality. For human dirofilariasis, treatment by surgical excision of the worm without systemic antiparasitic drugs is sufficient, whereas for B. malayi infections, systemic antiparasitic drugs are curative. However, loiasis treatment requires both surgical excision and systemic antiparasitic drugs³.

REFERENCES

• ¹
  Sabu L, Devada K, Subramanian H. Dirofilariosis in dogs and humans in Kerala. Indian J Med Res. 2005;121(5):691-3.
• ²
  Mathison BA, Couturier MR, Pritt BS. Diagnostic Identification and Differentiation of Microfilariae. J Clin Microbiol. 2019;57(10):e00706-19.
• ³
  Emukah E, Rakers LJ, Kahansim B, Miri ES, Nwoke BEB, Griswold E, et al. In Southern NigeriaLoa loaBlood Microfilaria Density is Very Low Even in Areas with High Prevalence of Loiasis: Results of a Survey Using the New LoaScope Technology. Am J Trop Med Hyg. 2018;99(1):116-23.

• Financial Support: No funding received.

Publication Dates

• Publication in this collection
  18 Aug 2021
• Date of issue
  2021

History

• Received
  16 June 2021
• Accepted
  07 July 2021