Microscopy (page 1 of 2)

Wuchereria bancrofti

The microfilaria of Wuchereria bancrofti are sheathed and measure 240-300 µm in stained blood smears and 275-320 µm in 2% formalin.  They have a gently curved body, and a tail that is tapered to a point.  The nuclear column (the cells that constitute the body of the microfilaria) is loosely packed; the cells can be visualized individually and do not extend to the tip of the tail.  Microfilariae circulate in the blood.

A	B

A, B: Microfilariae of W. bancrofti in thick blood smears stained with Giemsa.  Images courtesy of the Oregon State Public Health Laboratory.

Brugia spp.

Microfilariae of Brugia malayi are sheathed and in stained blood smears measure 175-230 µm.  In 2% formalin they are longer, measuring 240-300 µm. The tail is tapered, with a significant gap between the terminal and subterminal nuclei.  Microfilaria circulate in the blood.

C	D

C: Microfilaria of B. malayi in a thick blood smear, stained with Giemsa.
D: Microfilaria of B. malayi in a thin blood smear, stained with Giemsa.

Microfilaria of Brugia timori are sheathed and measure on average 310 µm in stained blood smears and 340 µm in 2% formalin.  Microfilaria of B. timori differ from B. malayi by a having a longer cephalic space, a sheath that does not stain with Giemsa, and a larger number of single-file nuclei towards the tail.  Microfilariae circulate in the blood.

E	F

E, F: Microfilariae of B. timori in a thick blood smear from a patient from Indonesia, stained with Giemsa and captured at 500x oil magnification.  Images from a specimen courtesy of Dr. Thomas C. Orihel, Tulane University, New Orleans, LA.

G	H

G: Sections of adults of Brugia sp. from a lymph node stained with hematoxylin and eosin (H&E), taken at 200x magnification.
H: Sections of adults of Brugia sp. from the conjunctiva of a patient from Ecuador, stained with H&E.  Image taken at 200x magnification.

Onchocerca volvulus

Microfilariae of Onchocerca volvulus are unsheathed and measure 300-315 µm in length.  The tail tapers to a point and is often sharply bent.  The nuclei do not extend to the tip of the tail.  Microfilariae typically reside in skin but may be found in blood or urine during heavy infections, or invade the eye and cause a condition known as river blindness.

I	J

I: Microfilariae of O. volvulus from a skin nodule of a patient from Zambia, stained with H&E.  Image taken at 1000x oil magnification.
J: Coiled microfilaria of O. volvulus, in a skin nodule from a patient from Zambia, stained with H&E.  Image taken at 1000x oil magnification.

Adult males of Onchocerca volvulus measure 15-45 mm in length; females are 30-50 cm.  Adults usually reside in nodules (onchocercomas) in subcutaneous tissue.

K	L

K, L:  Adults of O. volvulus in a subcutaneous nodule, stained with H&E.