Filaria colonies (adult male, female and eggs) on the cytology smears
- Cytology smears show many coiled and uncoiled filaria along plenty of unfertilized eggs without sheath and few sheathed fertilized eggs (marked with arrow) in a neutrophil rich inflammatory background
- Few filaria (marked structures) show blunt mouth part, while pointed tail region, without presence of nuclei, suggesting the evidence of Wuchereria bancrofti
- Single small size adult male worm is seen (yellow circle)
- Occasional epithelioid non-necrotising granulomas are seen
- Eosinophils and giant cells are not seen
Practical Points of Pathoclinics:
- Common nematode causing filariasis are Wuchereria bancrofti, Onchocerca volvulus and Brugia malayi. Mosquitoes are the intermediate hosts and vectors. Wuchereria bancrofti account for more than 90% of filaria cases, followed by Brugia malayi and Brugia timori. Most of the infection encountered in India and Nepal are by Wuchereria bancrofti. Wuchereria bancrofti are larger and longer along with curved body shape, and nuclei do not reach up to the tail end. Brugia malayi are smaller and irregular in shape with unequal size tightly packed nuclei.
- For specific typing of filaria, one need to look for (1) presence or absence of the sheath (2) shape and size of filaria and (3) presence of nuclei in the tip of the tail. Wuchereria bancrofti, Brugia malayi and Loa Loa, all have presence of sheath. However, they differ in presence of nuclei: nuclei are not seen in the tip of the tail region in Wuchereria bancrofti, while Brugia malayi have only 2 distinct nuclei in the tip of the tail region. Loa loa have nuclei, which are reaching up to the tip of the tail. Onchocerca volvulus, Mansonella perstans, Mansonella ozzardi and Mansonella streptocerca, all have absence of sheath. They also only partially differ in presence of nuclei: nuclei are not seen in the tip of the tail region in both Onchocerca volvulus and Mansonella ozzardi, while nuclei are reaching up to tip of the tail region in both Mansonella perstans and Mansonella streptocerca. Mansonella streptocerca have hooked tail.
- Filaria stay in the lymphatic system for years. Common site are cervical, axillary, and inguinal lymph nodes. Filaria can be aspirated from lymph nodes, lung, breast, thyroid, para-testicular region including epididymis, spermatic cord and soft tissue. Most cases are asymptomatic and transmit infection to others. In majority, microfilaria, adult worms and eggs have been incidentally detected on cytology smears in clinically unsuspected cases.
- Cytological diagnosis is easy and conveniently achieved by FNAC, without any requirement of biopsy. A low power screening is necessary to identify the microfilaria, as in most cases filaria are usually very scanty. In most cases cytological diagnosis does not pose any difficulties and can be helpful to avoid surgical excision. Sometimes fragments of dead calcified organisms can be seen in old long-standing cases.
- Early cytologic diagnosis can help in the initiation of diethylcarbamazine with albendazole, so severe manifestation of filariasis can be prevented. Diethylcarbamazine with albendazole is used to treat lymphatic filariasis as well as other helminths, particularly intestinal worms, which are commonly found to coinfect individual with filariasis in filarial-endemic region.
Reference: Kumar B, Karki S, Yadava SK. Role of fine needle aspiration cytology in diagnosis of filarial infestation. Diagn Cytopathol. 2011 Jan;39(1):8-12. doi: 10.1002/dc.21314. PMID: 20091903.