Ensuring diagnostic vigilance: Mandatory peripheral blood smear and fine needle aspiration in filarial endemic regions

Ensuring diagnostic vigilance: Mandatory peripheral blood smear and fine needle aspiration in filarial endemic regionsDespite the establishment of the National Filaria Control Program in 1955, filariasis poses an important public health challenge in India.Presently, an estimated 31 million individuals may carry microfilariae, with 23 million experiencing symptomatic filariasis, and approximately 473 million people are at risk of infection.Progress over the past decade has introduced novel diagnostic and treatment methodologies along with enhanced control approaches for filariasis.The updated strategy focuses on curbing transmission through mass treatment and managing individual patients to control the disease.India, having ratified the 50th World Health Assembly resolution for global lymphatic filariasis elimination in 1997, initiated a revised filariasis control program across 13 districts in 7 endemic states. 1 This effort included mass drug administration.Achieving interruption of transmission and elimination requires high treatment coverage, likely exceeding 85%.Therefore, effective drug delivery strategies tailored to regional variations are urgently needed.The endemicity of the disease requires robust advocacy tools and strategies, along with mechanisms to monitor and evaluate the impact of the elimination program.Lymphatic filariasis is one of India's neglected tropical diseases.Alongside implementing disability prevention and management strategies to reduce the occurrence of lymphoedema, there is a need for careful evaluation of diagnostic approaches. 2 We emphasise that selective peripheral smear examination guided by presence of eosinophilia, raised absolute eosinophil count, or fine needle aspiration cytology (FNAC) in unexplained lymphadenopathy or soft tissue lesions may be a more rational and cost-effective approach in endemic regions.However, clinically significant solitary lymph node swelling unexplained by any pathology, or multiple lymph node involvement, must have a lower threshold for fine needle aspiration, even in the absence of other visceral findings such as hepatosplenomegaly.We have encountered patients who had normal complete blood counts (CBC) but harboured microfilariae (Fig. 1), and physicians did not order peripheral smear examination.As pathologists, we routinely do peripheral smears and scrutinise them for microfilariae, irrespective of physician directives, frequently identifying these.Recently, we discovered microfilariae in the peripheral smear of a 16-year-old girl with only mild fever and no overt filarial symptoms.Timely administration of diethylcarbamazine citrate (for example, at the stage of microfilaremia) has been shown to kill adult filarial worms and reduce progression to lymphoedema, thus offering a window for curative intervention before chronic complications become established. 3Furthermore, we have observed instances of microfilariae in FNAC samples from various sites such as thyroid nodules (Fig. 2), inguinal lymph nodes (Fig. 3), and breasts. 4Thus, peripheral smears should be prioritized in those with eosinophilia or clinical suspicion, while FNAC remains valuable for detecting parasites in unsuspected soft tissue lesions. 5icrofilariae are more reliably detected in peripheral blood smears taken at night (typically 10 p.m.-2 a.m.), whereas daytime smears have a low yield.Instead, antigen detection tests (e.g.Filariasis test strip by Abbott, Standard Q test by SD Biosciences) offer a more feasible approach, as they can be done at any time of day. 6Although these tests are expensive and not universally available, advocating for their availability in primary health centres Correspondence FIG 1. Microfilaria in peripheral smear (100, Leishman's stain)