Review of Dancing Parasites in Lymphatic Filariasis

Abstract

Lymphatic filariasis is an infection transmitted by blood-sucking mosquitoes with filarial nematodes of the species Wuchereria bancrofti, Brugia malayi und B. timori . It is prevalent in tropical countries throughout the world, with more than 60 million people infected and more than 1 billion living in areas with the risk of transmission. Worm larvae with a length of less than 1 mm are transmitted by mosquitoes, develop in human lymphatic tissue to adult worms with a length of 7-10 cm, live in the human body for up to 10 years and produce millions of microfilariae, which can be transmitted further by mosquitoes. The adult worms can be easily observed by ultrasonography because of their size and fast movements (the so-called "filarial dance sign"), which can be differentiated from other movements (e. g., blood in venous vessels) by their characteristic movement profile in pulsed-wave Doppler mode. Therapeutic options include (combinations of) ivermectin, albendazole, diethylcarbamazine and doxycycline. The latter depletes endosymbiotic Wolbachia bacteria from the worms and thus sterilizes and later kills the adult worms (macrofilaricidal or adulticidal effect).

Keywords: contrast-enhanced ultrasound; elastography; guideline; parasite.

Fig. 1

Leg filariasis, B-mode imaging of leg filariasis a , color Doppler imaging of leg filariasis b in a patient with subcutaneous thickening.

Fig. 2

60-year-old patient from Guatemala, Latin America with recurrent scrotal swelling with thickness of the pure scrotum without testis of > 40 mm a and b , the swelling is indicated between markers) on both sides b . A hydrocele was operated on a few years ago. Treatment with mebendazole has been reported during that time. The “filarial dance sign” could be seen on real-time ultrasound below the testis. The testes showed increased stiffness using elastography c and little contrast enhancement on contrast-enhanced ultrasound d , indicating chronic orchitis. MRI images (T2, koronar) are also shown e , f .

Fig. 3

Ultrasound of enlarged lymph vessels in the scrotal area; in the left part of the biggest vessel, a moving worm can be detected a . On pulse wave Doppler, the movements appear as irregular amplitudes b and can be differentiated from pulsating vessels c .

Fig. 4

Lymph scrotum with thickened skin a . Thickness can be measured by ultrasound b .

Fig. 5

Breast filariasis. B-mode imaging a and color Doppler imaging of breast filariasis b . Irregular amplitudes of color signals could be used to make a differential diagnosis.

Fig. 6

Cord filariasis, grayscale imaging of cord filariasis a , detailed view of small adult worms b .