Identification of Microfilaria

 

Note:

(1) The length of the microfilaria is about 20% longer in formalin fixed preparations.

(2) Sheathed microfilaria may lose their sheath sometimes

(3) Hematoxylin is better for demonstrating the presence of a sheath than Giemsa.

(4) Patients may be infected by more than one type of microfilaria.

 

Wuchereria bancrofti:

(1) World distribution: worldwide in tropical and subtropical zones

(2) involves: lymphatics, seen in hydrocele fluid

(3) circulation in blood: nocturnal (periodic); in South Pacific subperiodic (test in afternoon)

(4) sheath on hematoxylin stain: present

(5) sheath on Giemsa stain: present

(6) length in blood smears: 260 (244-296) µm

(7) cephalic space: short, less than or equal to diameter of head

(8) nuclei in tail: none

(9) tail shape: pointed

 

Brugia malayi:

(1) World distribution: Asia and Indian subcontinent

(2) involves: lymphatics

(3) circulation in blood: nocturnal (periodic) or subperiodic (test in afternoon)

(4) sheath on hematoxylin stain: present

(5) sheath on Giemsa stain: may be absent; if present it is a bright pink

(6) length in blood smears: 220 (177-230) µm

(7) cephalic space:

(8) nuclei in tail: two isolated nuclei, subterminal and terminal

(9) tail shape: blunt

 

Brugia timori:

(1) World distribution: eastern end of Indonesian archipelago

(2) involves: lymphatics

(3) circulation in blood: nocturnal

(4) sheath on hematoxylin stain: present

(5) sheath on Giemsa stain: usually absent

(6) length in blood smears: 310 (290-325) µm

(7) cephalic space:

(8) nuclei in tail: two isolated nuclei, subterminal and terminal

(9) tail shape:

 

Loa loa:

(1) World distribution: West and Central Africa

(2) involves: subcutaneous tissue, conjunctivae

(3) circulation in blood: diurnal periodicity

(4) sheath on hematoxylin stain: present

(5) sheath on Giemsa stain: absent

(6) length in blood smears: 275 (250-300) µm; 238 (231-250) µm

(7) cephalic space:

(8) nuclei in tail: nuclei extend to the end of the tail

(9) tail shape:

 

Mansonella ozzardi:

(1) World distribution: Central America, South America, Caribbean islands

(2) involves: subcutaneous tissue

(3) circulation in blood: no periodicity

(4) sheath on hematoxylin stain: absent

(5) sheath on Giemsa stain: absent

(6) length in blood smears: 200 (173-240) µm; 183 (163-203) µm

(7) cephalic space:

(8) nuclei in tail: none

(9) tail shape: long, attenuated, sharply pointed

(10) comments: may be found together with M. perstans

 

Mansonella perstans:

(1) World distribution: tropical Africa, tropical South America

(2) involves: abdominal cavity and mesentery

(3) circulation in blood: no periodicity

(4) sheath on hematoxylin stain: absent

(5) sheath on Giemsa stain: absent

(6) length in blood smears: 195 (190-200) µm

(7) cephalic space:

(8) nuclei in tail: nuclei fill tail, extending to tip

(9) tail shape: blunt

(10) comments: may be found together with M. ozzardi

 

Mansonella streptocerca:

(1) World distribution: rain forests of Africa

(2) involves: skin

(3) circulation in blood: no periodicity

(4) sheath on hematoxylin stain: absent

(5) sheath on Giemsa stain: absent

(6) length from skin snips: 210 µm (180-240) µm

(7) cephalic space:

(8) nuclei in tail: extends to the end of the tail in a single row

(9) tail shape: crooked, blunt

(10) comments: may be found in skin snips

 

Onchocerca volvulus:

(1) World distribution: Central Africa, Middle East, Central America, northern South America

(2) involves: skin, subcutaneous and deeper tissues

(3) circulation in blood: no periodicity

(4) sheath on hematoxylin stain: absent

(5) sheath on Giemsa stain: absent

(6) length from skin snips: 309 (304-315) µm; 254 (221-287) µm

(7) cephalic space: more than 1.5 times diameter of head

(8) nuclei in tail: none

(9) tail shape: tapered to point, usually bent or flexed to 90°

(10) comments: may be found in skin snips

 

Identification Key

Nuclei	Length	Other	Diagnosis
no nuclei in tail tip	< 240 µm	no sheath; tail long, attentuated and sharply pointed	M. ozzardi
	> 240 µm	no sheath, tail tapered to a point and usually flexed to 90°, with cephalic space more than 1.5 times the diameter	O. volvulus
	> 240 µm	sheath on either Giemsa or hematoxylin, tail pointed	W. bancrofti
subterminal and terminal nuclei	< 250 µm		B. malayi
	> 250 µm		B timori
nuclei to tip	< 240 µm	no sheath, single row of nuclei, curved/crooked tai	M. streptocerca
	> 230 µm	sheath on hematoxylin stain, no sheath on Giemsa	L. loa
	< 200 µm	no sheath	M. perstans