FILARIAL WORMS

Dr. R.Someshwaran, MBBS, MD., Assistant Professor,

Department of Microbiology,

Karpagam Faculty of Medical Sciences and Research,

Othakalmandapam, Coimbatore-641032

Objectives of today’s class

• To enlist the human filarial worms (Nematodes)

• To understand and explain the morphology, life cycle, clinical presentation and pathogenesis of various filarial worms infecting humans

• To understand and explain the lab diagnosis, treatment and prevention of various filarial worms infecting humans

HELMINTHOLOGY

• Helminths are multicellular, bilaterally symmetrical animals

• Helminths – 2 Phylum

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Nemahelminthes

Nematodes

Platyhelminthes

Cestodes & Trematodes

Differences between Cestodes, Trematodes & Nematodes

CESTODES TREMATODES NEMATODES

Shape Tape like segmented

Leaf like unsegmented

Elongated,cylindrical, unsegmented

Sexes Sexes not separateMonoeciousHermaphrodite

Sexes not separateMonoecious except Schistosoma

Sexes are separateDiecious

Head end Suckers, often with hooks

Suckers, no hooks No suckers, no hooks, well developed

Alimentary canal

Absent Present,incomplete, no anus

Present, complete, anus present

Body cavity Absent Absent Present

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NEMATODES CLASSIFICATION(LOCATION OF ADULT IN BODY)

• INTESTINAL NEMATODES:a. Small intestine: Ascaris, Ancylostoma, Necator,

Strongyloides, Trichinella.b. Large intestine: Enterobius, Trichuris

• TISSUE NEMATODES (Somatic nematodes):a. Lymphatic: Wuchereria, Brugiab. Sub-cutaneous: Loa loa, Onchocerca, Dracunculusc. Mesentry: Mansonella spp.,d. Conjucntiva: Loa loae. Zoonotic filariasis: Dirofilaria spp.,

NEMATODES CLASSIFICATION(MODE OF INFECTION)

i. By ingestion:

a. Eggs: Ascaris, Enterobius, Trichuris

b. Larvae within intermediate host: Dracunculus

c. Encysted larvae in the muscle: Trichinella

ii. By Penetration of Skin: Ancylostoma, Necator, Strongyloides

iii. By blood sucking insects: Filariae

iv. By inhalation of dust containing eggs: Ascaris, Enterobius

NEMATODES CLASSIFICATION(BASED ON THEY LAY EGGS/LARVAE)

i. Oviparous: Egg laying nematodes

a. Unsegmented eggs: Ascaris, trichuris

b. Segmented eggs: Ancylostoma, Necator

c. Eggs containing larvae: Enterobius

ii. Viviparous: Producing larvae

Ex: Trichinella, Wuchereria, Brugia, Dracunculus

iii. Ovoviviparous: Laying eggs containing fully formed larvae which hatch out immediately: Strongyloides.

HUMAN FILARIAL WORMS

• Filarial worms belong to Superfamily: Filarioideae.

• Thread like worms transmitted by blood sucking insects (Arthropods)

• Vector borne disease / Zoonotic disease

• Infection by any filarial worm is called as ‘Filariasis’.

• Morphological forms: Adult worm & Microfilariae (embryo)

HUMAN FILARIAL WORMS

• Microfilaria (mf): Sheathed & Unsheathed/naked

• Sheathed mf: Retain their egg membrane

• Unsheathed mf: Ruptures out from the egg membranes

• 8 species of filarial worms infect humans

• Humans are the Definite hosts

Classification of Human filarial worms

A. Lymphatic filariasis:

a. Wuchereria bancrofti (Bancroftian filariasis)

b. Brugia malayi (Malayan filariasis)

c. Brugia timori

B. Subcutaneous filariasis:

a. Loa loa (Calabar swelling/Fugitive swelling)

b. Onchocerca volvulus (River blindness, dermatitis) &

c. Mansonella streptocerca (Skin diseases)

C. Serous cavity filariasis:

a. Mansonella ozzardi (Non-pathogenic) &

b. Mansonella perstans (Non-pathogenic)

Classification of Human filarial worms

D. Zoonotic filariasis:

a. Dirofilaria immitis

b. Dirofilaria repens

c. Brugia pahangi

d. Brugia beaveri

e. Brugia leporis

Filarial nematode

Habitat of Adults Habitat of Microfilaria

Vector Microfilaria periodicity

LYMPHATIC FILARIASISWuchereriabancrofti

Lymphatic tissue Blood Culex quinquefasciatus (W)Anopheles in rural AfricaAedes spp.,

Nocturnal (M)

Sub-periodic (R)

Brugia malayi Lymphatic tissue Blood Mansonia spp., AnophelesMansonia spp., Coquillettidia

Nocturnal (M)Sub-periodic (R)

Brugia timori Lymphatic tissue Blood Anopheles barbirostris Nocturnal

SUBCUTANEOUS FILARIASISLoa loa Subcutaneous

tissue, ConjunctivaBlood Chrysops (Deer fly) Diurnal

Onchocercavolvulus

Subcutaneous tissue

Skin and eye Simulium (Black fly) None

Mansonellastreptocerca

Subcutaneous tissue

Skin Culicoides (Midges) None

SEROUS CAVITY FILARIASISMansonellaperstans

Body cavities, Mesentry

Blood Culicoides (Midges) None

Mansonella ozzardi Body cavities Blood Culicoides (Midges)Simulium (Black fly)

None

Filarial nematode Characteristic feature of Microfilaria Epidemiology

LYMPHATIC FILARIASISWuchereria bancrofti Sheathed, Pointed tail tip free of nuclei South America,

Africa, Asia

Brugia malayi Sheathed, blunted tail tip with two terminal nuclei

Pacific Islands

Brugia timori Sheathed longer than Mf. malayi SE Asia, India, Indonesia

SUBCUTANEOUS FILARIASISLoa loa Sheathed, nuclei extending up to pointed tail tip West and Central

Africa

Onchocerca volvulus Unsheathed, blunt tail tip free of nuclei S. And C. America and Africa

Mansonellastreptocerca

Unsheathed, blunt tail tip with nuclei W. And C. Africa

SEROUS CAVITY FILARIASISMansonella perstans Unsheathed, pointed tail tip free of nuclei S. And C. America

Mansonella ozzardi Unsheathed, pointed tail tip with nuclei S. And C. America Carribean Islands

Head and Tail ends of Microfilariae

LYMPHATIC FILARIASIS

• Wuchereria bancrofti

• Brugia malayi

• Brugia timoria

Global Scenario

• Population at risk : 1.2 Billion

• No. of countries : > 80

• Mf carriers : 76 Million

• Diseased : 44 Million

• Hydrocele : 27 Million

• Lymphoedema : 16 Million

• TPE : 1 Million

National Scenario

• Total Population : 110 C

• Population at risk : 45.4 C (in 16 States & 5 UT’s)

• Total infected : 51.7 M(Wb - 99.4 % and Bm - 0.6 %)

• No. of diseased : 22.5 M

• Mf carriers : 29.2 M

• Hydrocele : 12.9 M

EPIDEMIOLOGY

Mode of Transmission & Incubation Period

• Lymphatic Filariasis is transmitted by the biteof Infected mosquito which harbours L3 larva.

• L1: 1-3 hours

• L2: 3-4 days

• L3: 5-6 days

• Pre-patent period: (L3 to Mf) Not known

• Clinical Incubation period: 8-16 months

Clinical Manifestations

• Manifestations are 2 types

1. Lymphatic Filariasis (Presence of Adult worms)

2. Occult Filariasis (Immuno hyper responsiveness)

Clinical Spectrum

None Asymptomatic

microfilaremiaFilarial

fever

Chronic

pathologyTPE

Stages in Lymphatic Filariasis

• There are 4 stages :

1. Asymptomatic amicrofilariaemic stage

2. Asymptomatic microfilariaemic stage

3. Stage of Acute manifestation

4. Stage of Obstructive (Chronic) lesions

Wuchereria bancrofti

Bancroftian Filariasis

Wuchereria bancrofti

Wuchereria bancrofti - Adult

LIFECYCLE OF W. bancrofti

Filarial fever

Complications

Lab diagnosis

Laboratory Diagnosis

1. Demonstration of microfilarae in the peripheral blood

a. Thick blood smear: 2-3 drops of free flowing blood by finger prick method, stained with JSB-II

b. Membrane filtration method: 1-2 ml intravenous blood filtered through 3µm pore size membrane filter

c. DEC provocative test (2mg/Kg): Afterconsuming DEC, mf enters into the peripheralblood in day time within 30 - 45 minutes.

2. Immuno Chromatographic Test (ICT): Antigendetection assay can be done by Card test andthrough ELISA. Circulating Filarial Antigendetection is regarded as “Gold Standard” fordiagnosing Wuchereria bancrofti infection.Specificity is near complete, sensitivity isgreater than all other parasite detection assays,will detect antigen in amicrofilaraemic as wellas with clinical manifestations likelymphoedema, elephantiasis.

3. Quantitative Blood Count (QBC):QBC will identify the microfilariae and will help instudying the morphology. Though quick it is notsensitive than blood smear examination.

4. Ultrasonography:Ultrasonography using a 7.5 MHz or 10 MHz probe canlocate and visualize the movements of living adultworms of W.b. in the scrotal lymphatics ofasymptomatic males with microfilaraemia. Theconstant thrashing movements described as “Filariadance sign” can be visualized.

5. Lymphoscintigraphy:The structure and function of the lymphatics of theinvolved limbs can be assessed by lymphoscintigraphyafter injecting radio-labelled albumin or dextran in theweb space of the toes. The structural changes can beimaged using a Gamma camera. Lymphatic dilation &obstruction can be directly demonstrated even in earlyclinically asymptomatic stage of the disease.

6. X-ray Diagnosis:X-ray are helpful in the diagnosis of Tropical pulmonaryeosinophilia.

Picture will show interstial thickening, diffused nodularmottling.

7. Haematology : Increase in eosinophil count

Peripheral smear showing Microfilaria

CLASSICAL FILARIASIS vs OCCULT FILARIASIS

CLASSICAL FILARIASIS OCCULT FILARIASIS

CAUSE Inflammatory changes to Devoloping worms and adult

Hypersensitivity reaction to Microfilaria antigen

PATHOLOGY Acute inflammation and epitheloid granuloma

Eosinophilic granuloma

ORGANS AFFECTED Lymph nodes & Lymphatic system

Lung, liver and spleen

MICROFILARIA Present in blood Present in affected tissues & absent in blood

THERAPEUTIC RESPONSE No response Responds to microfilaricidal agent

SEROLOGICAL TESTS Antobody not diagnostic IgE Ab Highly sensitive

DEC PROVOCATION TEST

• Diethyl carbamazine 2mg/kg Body weight

• 20-50 mins later – peripheral smear for microfilariae.

Post DEC Provocation test

Tropical Pulmonary Eosinophilia

Brugia malayi

Malayan Filariasis

LIFE CYCLE

Brugia malayi

Brugia malayi

Microfilaria of Wuchereria bancrofti& Brugia malayi

Features Wuchereria bancrofti Brugia malayi

Appearance Graceful sweeping curves Kinky with 2⁰ curves

Size 250-300 micrometres long 175 to 230 micrometres

Cephalic space Length to width ratio 1:1 Length to width ratio 2:1

Stylet at anterior end Single Double

Excretory pore Not prominent Prominent

Nuclei column Large coarse discrete nuclei Overlapping blurred nuclei

Tail Pointed & free of nuclei Pointed with 2 distinct nuclei

Sheath Faintly stained Well stained

Wuchereria bancrofti

Brugia timori

Lymphatic filariasis

Brugia timori

Loa loa

• African eye worm

• Calabar swelling

• Fugitive swelling

• Adult: 3-7cm long

• Treatment: Dec. Surgical removal

CALABAR SWELLING

Loa loa Subcutaneous nodules

LIFE CYCLE

Loa loa

Onchocerca volvulus

River blindness

Convoluted or Blinding filaria

50cm long adult worm

Onchocerca volvulus

Onchocerca volvulus

Mazzotti reaction

• DEC treatment causes intense reaction with rash, pruritus, facial edema, fever, hypotension, lymphadenopathy and occ. Eye damage.

• Drug of choice is Ivermectin

Life cycle

Mansonella streptocerca

• Subcutaneous filariasis

Life cycle

Mansonella ozzardi

Mansonella perstans

• Usually nonpathogenic

Mansonella perstans

Zoonotic filariasis

• Dirofilaria immitis – Dog heart worm

• Dirofilaria repens (dogs) – subcutaneous and conjunctival nodules in humans

• Dirofilaria conjunctivae (humans)

• Brugia pahangi- cats and dogs

Dirofilaria immitis

Dirofilaria immitis

Dirofilaria repens

Brugia pahangi

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