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Peripheral blood eosinophilia can occur in many diseases, most common being parasitic, followed by allergic and infectious, and neoplastic conditions, including primary hematologic diseases ¹.

A 35-year-old male from eastern India, an endemic region for lymphatic filariasis, presented to a tertiary care centre of northwestern India. During a routine annual medical examination was found to have severe eosinophilia (7.64 × 10⁹/L). The patient was asymptomatic, and clinical examination did not reveal any abnormality. A thick peripheral blood smear collected at 10 PM demonstrated microfilaria with gentle body curves, loosely packed nuclei which were not extending till the tail (Wuchereria bancrofti) as shown in Figure. The patient was treated with diethylcarbamazine (DEC) for 12 days. On follow-up after 3 weeks the eosinophil counts normalized, and microfilaria had disappeared from the blood.

Wuchereria bancrofti is transmitted by the Culex quinquefasciatus, is been the predominant infection contributing to >90% of cases in India ². It can cause acute conditions like adenolymphangitis, Acute epididymo-orchitis and funiculitis. If left untreated, it  leads to chronic debilitating conditions like Lymphoedema, hydrocele, elephantiasis.

This case highlights the importance of considering occult filarial infection in patients with unexplained eosinophilia coming from endemic areas.

Figure shows Wuchereria bancrofti microfilaria in the thick smear, Leishman stain.

References:

1.      Weller PF. Eosinophilia and eosinophil-related disorders. In: Adkinson NF, Yunginger JW, Busse WWea, editors. Allergy: Principles and Practices. 6th ed. St. Louis: Mosby-Year Book; 2003. pp. 1105–1555. 

2.      Agrawal VK, Sashindran VK. Lymphatic Filariasis in India : Problems, Challenges and New Initiatives. Med J Armed Forces India. 2006 Oct;62(4):359-62. doi: 10.1016/S0377-1237(06)80109-7. Epub 2011 Jul 21. PMID: 27688542; PMCID: PMC5034168.