Lecture #3: THE BLOOD and TISSUE NEMATODES

 Characteristics in general

1.     They are anthropod transmitted.

2.     They are transmitted via skin inoculation.

3.     They have 2 phases of development.

a.     One is taking place within the vertebrate host.

b.     One was taking place within the vertebrate host which also acts as a vector.

Morphology

1. Adults – threadlike and creamy in appearance and varies in length. They are formed in different lymphatics or body cavities. 

2. Larva – eggs laid are embryonated which when hatched are called microfilaria. If it escapes from its shell, it is said to be unsheathed, otherwise, it is sheathed. They are snake–like in appearance with column of cells from the anterior most portions down to the posterior end.

Location of microfilaria in man

1. Peripheral blood – W. bancrofti, A. perstans, L. loa, B. malayi,

2. Lymph spaces of skin, subcutaneous nodules – O. volvulus

3. No microfilarial stage in man, female discharges rhabditoid larva – D. medinensis

Important properties of microfilaria

1. Exhibit periodicity 

a. Periodic – if there is a required time for microfilaria to recover.

(1)   Nocturnal – night (10pm – 2am)

(2)   Diurnal – day (10am – 2pm)

b. Sub–periodic – if microfilaria is recovered by day and night time.

(1)   Nocturnal – peak count is at night.

(2)   Diurnal – peak count is at daytime.

c. Non–periodic – if count both night and day is the same.

2.     Presence of sheath

a. Sheathed microfilaria                          Habitat

(1)   Wuchereria bancrofti                      lower lymphatics

(2)   Brugia malayi                                   upper lymphatics

(3)   Loa loa                                               subcutaneous tissues 

b. Unsheathed microfilaria                     Habitat

(1) Onchocerca volvulus                       subcutaneous nodules

(2) Dipetalonema streptocercum        skin and subcutaneous tissues

(3) Dipetalonema perstans                  body cavities (peripheral tissues)

(4) Mansonella ozzardi                         body cavities (mesentery fats)

(5) Dracunculus medinensis               visceral, in subcutaneous tissues

Laboratory diagnosis

1. Finger prick (Capillary blood)

a.     Unstained smear + 3% HAc

b.     Giemsa stained smear

c.      Capillary tube method (buffy coat layer) 

2. Venous blood

a.     Knotts concentration technique

3. CSA (citrate saponin acid) method

COMPARISON OF SHEATHED MICROFILARIA
	Wuchereria bancrofti	Brugia malayi	Loa loa
Disease	Bancroftian filariasis Wucheriasis Elephantiasis	Malayan filariasis	Loaiasis Fugitive swelling Calabar swelling
Vectors	Anopheles minismus flavirostris	Mansonia bonneae	Chrysopps spp
	Aedes poecilus	Mansonia uniformis	Deer flies
	Culex pipiens quinquefasciatus	Anopheles spp.
Adults	The females measure 10 cm × 0.3 mm, while males remain considerably smaller (4 cm × 0.1 mm). A striking feature of adult worms is the ability to cause massive dilation of the surrounding and proximal lymphatics, indicating release and/or stimulation of potent lymphangiogenic factors by adult worms.	Thread–like roundworms which are coiled up in pairs in dilated lymphatics. There are two strains identified: the nocturnal periodic strain with their highest concentrations between the hours of 10pm and 2am, and the sub-periodic strain with their highest numbers being detected between noon and 8pm	Males measure about 34 mm, the caudal end curves ventral and is provided with a narrow wing.
			Females measure 60mm in length with the vulvar opening located in the cervical region.
Microfilaria	distinguished by the absence of nuclei at the tip of the tail.	2 stylets in the anterior end and 2 terminal nuclei at the tip of the tail with constriction in between, the column of cells is arranged compactly.	Sheathed with nuclei extending to the tip of the tail.

TAIL COMPARISON OF SHEATHED MICROFILARIA
Wuchereria bancrofti
Brugia malayi
Loa loa

ACANTHOCHEILONEMA PERSTAN

1.     Disease: Acanthocheilonemiasis, Dipetalonemiasis

2.     Better known as Dipetalonema perstans

3.     Adult found in mesentery, retroperitoneal tissues, pleural and pericardial cavities.

4.     Microfilariae are found in peripheral blood and lung capillaries.

5.     Intermediate host are blood sucking midges (Culicoides)

6.     Not very pathogenic, causes only minor allergy.

7.     Unsheathed microfilariae

MANZONELLA OZZARDI

1.     Disease: Mansonelliasis ozzardi, Ozzard’s filariasis 

2.     Adult inhabits body cavities, mesentery visceral fat. 

3.     Unsheathed, non–periodic and sharp–tailed microfilariae.

4.     Vector is Culicoides furens

5.     Nuclei do not extend up to the tip of the tail.

6.     Adult causes little damage; occasional hydrocele

DIPETALONEMA STREPTOCERCA

1.     Found in Africa (Congo & Ghana) 

2.     Adult worm unknown in man but found in chimpanzees.

3.     Unsheathed microfilariae in skin of man and chimpanzees

4.     Intermediate host is Culicoides grahami

DIROFILARIA IMMITIS

1.     Unsheathed microfilariae

2.     Natural infection in dogs, cats, wolves

3.     Microfilariae is not present in blood.

4.     Adult female worm in the right ventricle and pulmonary artery of the dog

5.     Symptoms in man includes cough and chest pains.

ONCHOCERCA VOLVULUS

1.     Disease: Onchocerciasis, onchocercosis, “coastal erysipelas,” “blinding filariasis,” “river blindness” 

2.     Found in Africa, Central and South America 

3.     Adult worms in tumors of subcutaneous tissues, nodules in pelvic arch, junction long bones, scalp

4.     Microfilariae rarely found in blood.

5.     They are found in lymphatics of cutaneous layers as well as in the stratum germinativum and corneal conjunctiva.

6.     Adult live more than 11 years

7.     Intermediate host is the black fly or gnat (Simulium) with development of fibrous encapsulation (benign lesion)

8.     Microfilaria and/ or metabolites of adult damage the optic nerve

9.     May cause elephantiasis of genitalia (external) in Congo.

10.  Dermoepidermatitis (filarial itch)

DRACUNCULUS MEDINENSIS

1.     Also known as medina worm, guinea worm, serpent worm, dragon worm of fiery serpent of Israelites.

2.     Causes: Dracunculiasis, dracumalosis, dracontiasis

3.     Transmitted by ingestion of infected cyclops in raw water.

4.     Female worm causes toxemia (relieved by epinephrine)

5.     Gravid female migrates to subcutaneous tissues or legs, arms, trunk, and shoulder and discharge the larvae from the ulcers when in contact with water.