Microscopy (page 2 of 2)

Loa loa

Microfilariae of Loa loa are sheathed an measure 230-250 µm long in stained blood smears and 270-300 µm in 2% formalin.  The tail is tapered and nuclei extend to the tip of the tail.  Microfilariae circulate in the blood.

M	N

M: Microfilaria of L. loa in a thin blood smear, stained with Giemsa.
N: Microfilaria of L. loa a thick blood smear from a patient from Cameroon, stained with Giemsa.  Note the nuclei extending to the tip of the tail to the left of the image.

O	P

O: Microfilaria of L. loa in a thick blood smear, stained with Giemsa.
P: Microfilariae of L. loa captured by the Knotts concentration technique.  Image taken at 500x magnification.

Mansonella spp.

Microfilariae of Mansonella perstans are unsheathed and measure 190-200 µm in stained blood smears and 180-225 µm in 2% formalin.  The tail is blunt and nuclei extend to the tip of the tail.  Microfilariae circulate in the blood.

Q	R

Q, R: Microfilariae of M. perstans in a thick blood smear stained with Giemsa, from a patient from Cameroon.

Microfilariae of Mansonella ozzardi are unsheathed and measure 160-205 µm in stained blood smears and 200-255 µm in 2% formalin.  The tail tapers to a point and the nuclei end well before the end of the tail.  The end of the tail is also bent in a small hook-like shape.  Microfilariae circulate in blood.

S	T

S, T: Microfilariae of M. ozzardi in thick blood smears, stained with Giemsa.

Microfilariae of Mansonella streptocerca are unsheathed and measure 180-240 µm.  The tail is been into a hook-like shape and the nuclei extend to the end of the tail.  Microfilariae are found in skin and do not circulate in the blood.

U

U: Microfilaria of M. streptocerca, fixed in 2% formalin and stained with hematoxylin.

Mixed filariases

It is not uncommon in endemic areas for patients to be infected with more than one species of filarial worm.  These infections most-commonly involve a species of Mansonella and another genus, or multiple species of Mansonella.

V

V: Mixed filariases of Loa loa (left) and Mansonella perstans (right) in a thick blood smear from a patient from Cameroon, stained with Giemsa.

Dirofilaria spp.

The genus Dirofilaria consists of many species that infect a wide range of hosts worldwide, including carnivores, rodents and primates.  Humans are incidental hosts for several of these; the most frequent include D. immitis (dog heartworm), D. tenuis (raccoons) and D. repens (dogs).  The worms usually die before completing their development in the human host, but tend to follow the same migratory pathway as in the natural definitive host; D. tenuis and D. repens most often remain in the subcutaneous tissue where the dying worms produce a localized granulomatous nodule, or, in the case of D. immitis, pulmonary infarcts and/or nodules often appearing as coin lesions on X-ray.  Humans acquire Dirofilaria when bitten by mosquitoes, the arthropod vector and intermediate host.

W	X

W: Cross-sections of Dirofilaria sp. from a subcutaneous nodule above the right breast of a female patient who traveled to several western European countries, stained with H&E.  Image taken at 100x magnification.  Image courtesy of Dr. Truus Derks.
X: Higher magnification of the same specimen as Figure W, taken at 400x magnification.  Note the presence of the intestine (IN), lateral chords (blue arrows) and internal lateral ridge (black arrow).

Y	Z

Y: Cross-sections of Dirofilaria sp. from a subcutaneous nodule above the breast of a patient from Canada, stained with hematoxylin and eosin (H&E).  Image taken at 100x magnification
Z: Higher magnification of Figure Y, taken at 200x magnification.  Note the reproductive tubes (RT) that lie adjacent to the intestine (blue arrow).