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Microfilaria

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amit singh

on 28 July 2016

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Transcript of Microfilaria

Tissue Nematodes
INTRODUCTION
Infects different tissues
Major group: Filarial nematodes
Superfamily Filarioidea
Adult worms slender and thread-like, measuring 2-10 cm
Inhabit:
Circulatory and lymphatic channels
Connective tissue
Serous cavities
Female are viviparous i.e., giving birth to larvae K/a MICROFILARIAE
Some species retain their egg membrane, which form a sheath and k/a SHEATHED microfilariae
Those rupture their egg membrane are k/a UNSHEATHED microfilariae
Life cycle passed in two hosts:
Man
Certain blood-sucking insects
Infective form is microfilaria and its complete development occurs in insect host
Transmitted to man by insect bite
Species diagnosis is generally made by larval forms; adult worms are rarely obtained
According to the habitat of adult worm, human filarial infections are classified as follows:
Lymphatic filariasis
Subcutaneous filariasis
Serous cavity filariasis
Lymphatic filariasis:
Wuchereria bancrofti
Brugia malayi
Brugia timori
Subcutaneous filariasis
Loa loa
Onchocerca volvulus
Mansonella streptocerca
Serous cavity filariasis
Mansonella perstans
Mansonella ozzardi
Groups on the basis of presence and absence of sheath are
Sheathed microfilaria
Wuchereria bancrofti
Brugia malayi
Loa loa
Unsheathed microfilaria
Mansonella streptocerca
Mansonella ozzardi
Onchocerca volvulus
Differentiation on the basis of arrangement of nuclei in microfilaria
Sheathed microfilariae
Tail nuclei
Nuclei do not extend up to tip
Nuclei extend up to tip
Two nuclei at the tip of tail
Nuclei present in continuous row up to tail
Wuchereria bancrofti
Brugia malayi
Loa loa
Unsheathed microfilariae
Tail nuclei
Nuclei extend up to tip
Nuclei do not extend up to tip
Mansonella perstans
Mansonella streptocerca
Mansonella ozzardi
Onchocerca volvulus
Wuchereria bancrofti
Brugia malayi
Loa loa
M. perstans
M. ozzardi
M. streptocerca
O. volvulus
Periodicity:
Nocturnal:
Largest number of microfilaria in blood at night
E.g.: W. bancrofti, B. malayi, B. timori
Diurnal:
During day
Eg: Loa loa
Non-periodic:
Constant levels during day and night
Eg: Mansonella spp, O. volvulus
Sub-periodic:
Detected throughout the day but largest number during late afternoon or night
Wuchereria bancrofti
Geographical distribution:
Confined to tropics and subtropics
In India, along sea-coast and banks of big rivers
Habitat:
Lymphatic vessels and Lymph nodes
In man only, not zoonotic
MORPHOLOGY
Adult worms:
Transparent
Long-hair like
Creamy white
Filiform in shape, both ends tapering
Size:
Male: 2.5-4.0 cm X 0.1 mm
Female: 8-10cm X 0.2-0.3 mm
Tail end:
Male: Curved ventrally, contains two spicules
Female: Straight
Both remain coiled together, difficult to separate
Life span
: 5-10 years
Microfilariae
Colourless and transparent
Blunt heads and pointed tails
Measures 245-290 X 6-7 micrometer
Morphological pecularities:
Hyaline sheath:
Much longer than larval body
Moves within it
Represent chorionic envelope of egg
Cuticula
lined by subcuticular cells
Nuclei or somatic cells:
Granular
In central axis from head to tail
Does not extend up to tip of tail
Cephalic space in anterior end devoid of nuclei

Life cycle
Adult worm in lymphatic system of man
Male fertilises female
Microfilariae are discharged by the gravid female
Microfilariae in blood stream
Microfilariae are taken up by mosquito during blood meal
Infective larvae
Bite of mosquito
Larvae reach the lymphatic channels
Settle down in lymph nodes
Adult worms
Sheathed microfilariae taken up by female mosquito and reach the stomach
Cast off sheaths in 2-6 hrs
Penetrate gut-wall, reach thoracic muscles in 4-17 hrs
In next 2 days:
1st stage
larvae
Short, sausage, short spiky tail
125-250 X 10-17 micrometer
In 3-7 days:
2nd stage

larvae by 1/2 moulting (225-300 X 15-30 micrometer)
On 10-11th day,
3rd stage
(Infective) larvae (1400-2000 X 18-23 micrometer)
Migrate to proboscis sheath of mosquito
Development in mosquito
Intermediate host:
Culex
Aedes
Anopheles
Major vector in india: Culex fatigans
PATHOGENESIS
Infection is k/a Bancroftian Filariasis or Wuchereriasis
Two types of disease:
Classical filariasis
Occult filariasis
Lesion in Classical filariasis
Lymphangitis
Lymphadenitis
Elephantiasis
Lymphangiovarix
Hydrocele
Chyluria
Features Classical Filariasis Occult Filariasis

Cause
Developing worms and adults Microfilariae

Basic lesions
Acute inflammation followed by An eosinophilic granuloma
granuloma surrounding the adult
worm and a fibrous scar
Organs involved
Lymphatic system Lymphatic system, lungs,
liver and spleen
Microfilaria
Present in blood Present in affected tissue but
not in blood
Therpeutic response
No response to any drug Responds to DEC
Serological test
Complement fixation test not so Highly sensitive
sensitive
ELEPHANTIASIS
Affected part becomes enlarged
Tumour-like solidity
End-result of infection after years
Cause:
Fibrotic constriction of afferent lymphatics draining the part
Recurrent attack of lymphangitis
Excess protein causes hyperplasia and hypertrophy
In leg: Obstruction of inguinal or iliac LN
In scrotum: Superficial inguinal LN
Skin becomes rough, fissured and even papillomatous
Classical filariasis
Asymptomatic filariasis
Cases of light infections
Symptomatic filariasis
Two phases
Inflammatory phase:
Lymphangitis and Lymphadenitis
Last for few days
Subsides and recurs at regular intervals
Obstructive phase:
Varicose LN, Hydrocele, Chyluria, Elephantiasis
Found where inflammation occurs
Take long time 20 yrs to develop
Occult filariasis
Hypersensitivity reaction to microfilarial antigen leads to eosinophil granuloma
Massive eosinophilia 30-80%
Generalised LN enlargement
Hepatosplenomegaly
Pulmonary symptoms
Absence of Microfilaraemia
Lymphatic filariasis is absent
Tropical pulmonary eosinophilia
Manifestation of occult filariasis
Low grade fever
Loss of weight
Dry nocturnal cough
Dyspnoea and ashmatic wheezing
Marked eosinophilia
CXR shows mottled shadows similar to miliary TB
High level of serum IgE and filarial antibodies
Young adults are MC affected
Diagnosis of Filariasis
Direct Evidence
Indirect Evidence
Microfilariae
(Sheathed microfilariae having
tail-tip free from nuclei)
In the peripheral blood
In the chylous urine
In the exudate of lymph varix
In hydrocele fluid
Adult worms
In the biopsied LN
Calcified worm by X-ray
Allergic tests
Blood examination: Eosinophilia(5-15%)
Intradermal test: An immediate hypersensitivity reaction
Immunological test
Complement fixation test. Sensitive test for occult filariasis
Acridine orange-microhematocrit tube technique
Tube contains heparin, EDTA and acridine orange
Blood is added to tube and centrifuged
Buffy coat forms that contains the parasites
Acridine orange stains the DNA
Examine by flourescent microscope
Diethyl carbamazine (Hetrazan) provocation test
Microfilariae induced to appear in blood during day by single dose of 2mg/kg body weight DEC
Peak numbers occur after 15-20 min

Treatment and Prevention
DEC orally 6mg/kg body weight daily for 12 days
Preventive measures:
Control of vectors: DDT, malathion
Film of oil over water surface
Larvivorous fish may be added to pond
Improved sanitation
Brugia malayi
Geographical distribution:
In India, Far east and Southeast Asia
Kerala is largest endemic area
Others are Assam, Orissa, West Bengal, M.P.
Occur alone or with Bancroftian filaria
Habitat: Lymphatic system
Larger (290 X 7 micrometer)
Smaller (230 X 6 micrometer)
Mf. bancrofti
Mf. malayi
Life cycle
Similar to W. bancrofti
Intermediate hosts are
Mansonia
Anopheles
Aedes
In India: M. annulifera, M. indiana
Pathogenesis:
Causes brugian filariasis
Course is similar to bancroftian except there is no chyluria and involvement of male genitalia
Elephantiasis is restricted to legs
Treatment:
Similar to bancroftian filariasis
Loa Loa
Geographical distribution: Central and West Africa
Habitat: Subcutaneous tissues of man; often in the sub-conjunctival tissue of eye
Morphology:
Adult worm:
Cuticula have numerous rounded protuberances
Male measures 3 cm X 0.35 mm
Female measures 6 cm X 0.5 mm
Life span: 15 years or more
Microfilaria:
Found during day time in peripheral blood
Sheathed and measures 300 X 7 micrometer
Nuclei extends to tail-tip
Life cycle
Two hosts:
Man: Definitive host
Chrysops, a day biting female mangofly: Intermediate host
Insect bite and the larva enter the subcutaneous tissue and develop into adult worms
Microfilaria circulate in blood during day time and also found in S/C tissues
Pathogenesis
FUGITIVE OR CALABAR SWELLINGS:
Temporary swelling caused by wandering adult worm in subcutaneous tissue
Measures up to 3 cm in dia
Disappear in few days and reappear elsewhere
Hypersensitivity reactions to excretory products of worms
Lab diagnosis
Suggested by fugitive swelling
High eosinophilia
Specific diagnosis on demonstration of microfilariae in blood
ONCHOCERCA VOLVULUS
Common names : Convoluted filaria, river blindness or blinding filaria
2nd major cause of blindness in world
Morphology
Adult worms:
Whitish
Opaque and transparent with transverse striations
Post end curved, hence the name
Microfilariae
Unsheathed
Non-periodic
300 micrometer X 8 micrometer
Simulium a day biting female black flies as intermediate host
Life cycle same as loa loa
Pathogenesis on host's allergic and inflammatory reactions to worm
Microfilaria causes skin lesion: Dermatitis with pruritus and fibrosis
Mazzotti test:
Single dose of 50 mg DEC given orally
Development of itching and rash within 24 hours indicates presence of cutaneous microfilariae
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