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Infection - 3 closely related Nematodes

◦ Wuchereria bancrofti

◦ Brugia malayi

◦ Brugia timori

* Transmitted by the bite of infected mosquito responsible for

considerable sufferings/deformity and disability

* All the parasites have similar life cycle in man

* Adults seen in Lymphatic vessels

* Offsprings seen in peripheral blood during night

Lymphatic Filariasis

Filarial worms

◦ Tissue dwelling parasites

Possess a unique life cycle stage – the microfilaria - between the

egg and J1

Egg microfilaria J1 J2 J3 J4 Adult

these are present in the bloodstream or skin of the definitive host.

Filarial worms utilize arthropods as vectors

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Epidemiology

95% cases due to Wuchereria bancrofti, other species include

Brugia malayi and Brugia timori

120m people infected in >80 countries in Africa, Asia, the Pacific

islands and South and Central America

40m of those infected are disfigured or severely incapacitated

W. bancrofti usually resides in deeper lymphatic system besides

in lower lymphatic system, with no natural or reservoir host

B.malayi usually resides in lower lymphatic system of limb,

can be transmitted to cats and rhesus monkeys

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• W. bancrofti- broad equatorial belt particularly

Africa, Middle East, Southeast Asia, Indo-Pacific islands, Parts of

Australia and South America

• Brugia malayi - Orient, South Pacific, and Southern Asia to India –

overlaps with W. bancrofti - but does not occur in Africa or South America

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Man – Natural Host

Age – All age (6 months) Max: 20-30 years

Sex – Higher in men

Migration – leading to extension of infection to non-endemic

areas

Immunity – may develop after long year of exposure (Basis of

immunity-not known)

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Associated with Urbanization, Poverty, Industrialization,

Illiteracy and Poor sanitation.

Climate: is an important factor which influences:

1. The breeding of mosquito

2. Longevity (Optimum temperature 20-300C & Humidity

70%)

3. The development of parasite in the vector

4. Sanitation, Town planning, Sewage & Drainage.

Adults:

Thread-like, smooth cuticle, filariform oesophagus.

Female: 10 cm x 0.2 mm. (2 sets of genitalia, vulva 1mm from

anterior end)

Male: 4 cm x 0.1 mm. (one set of genitalia, posterior end curved

with2 spicules)

Takes 6-12 months for females to

release microfilariae

Produce for 5-10 years

♀

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Micrifilariae:

Embryos laid by the female

250 X 8µm, with graceful curves with

rounded anterior & posterior ends

Have loose redundant sheath

No alimentary canal

The body contains columns of nuclei

The tail is free of nuclei

Life span about 2~3 months

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Vector:

Wuchereria bancrofti is mainly

transmitted by

◦ Culex in India, Anopheline &

Aedes mosquitoes in Africa

B. malayi and B. timori are

transmitted mainly by Mansonia and

Anopheles

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Anopheles

Aedes

Culex

Mansonia

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W. bancrofti -10 PM to 2 AM

B. malayi - 8 PM to 4 AM

Theories:

Adaptation between biting & microfilariae

+ve chemotaxis between mosquito

saliva & microfilariae

↑ CO2 in blood stimulates microfilariae

to migrate to peripheral blood

Khalil’s theory: Blockage theory

Nocturnal periodicity of microfilariae

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Pathology

• Adult worms live in the afferent lymphatic vessels and cause

severe disruption to the lymphatic system

• Scrotal damage and massive swelling may occur when adult

Wuchereria bancrofti lodge in the lymphatics of the spermatic

cord

• Late stage disease is typified by elephantiasis – painful and

disfiguring swelling of the limbs

• Trauma and secondary bacterial infection of affected tissues is

common

• Incubation period: 1 year.

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Manifestations are 2 types

1. Lymphatic Filariasis (Presence of Adult worms)

2. Occult Filariasis (Immuno hyper responsiveness)

None Asymptomatic

microfilaremia Filarial

fever

Chronic

pathology TPE

Clinical Spectrum

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There are 4 stages :

1. Asymptomatic amicrofilariaemic stage

2. Asymptomatic microfilariaemic stage

3. Stage of Acute manifestation

4. Stage of Obstructive (Chronic) lesions

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In endemic areas, a proportion of population does not show mf

or clinical manifestation even though they have some degree

of exposure to infective larva similar to those who become

infected.

◦ Laboratory diagnostic techniques are not able to determine whether they

are infected or free.

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Considerable proportions are asymptomatic for months and

years

◦ they have circulating microfilariae

◦ important source of infection

◦ can be detected by Night Blood Survey and other suitable

procedures

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During initial months and years, there are recurrent episodes of

Acute inflammation in the lymph vessel/node of the limb &

scrotum that are related to bacterial & fungal super infections of

the tissue that are already compromised lymphatic function.

Clinical manifestations are consisting of:

1. Filarial fever

2. Lymphangitis

3. Lymphadinitis

4. Epididimo orchitis

Occult or Cryptic filariasis, in classical clinical manifestation

mf will be absent. Occult filariasis is believed to be the result

of hyper responsiveness to filarial antigens derived from mf.

Seen more in males.

◦ Patients present with paroxysmal cough and wheezing, low grade fever,

scanty sputum with occasional haemoptysis, adenopathy and increased

eosinophilia.

◦ X-ray shows diffused nodular mottling and interstial thickening

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Lymphoedema is classified into 7 stages on the basis of the presence

& absence of the following:

1. Oedema

2. Folds

3. Knobs

4. Mossy foot

5. Disability

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Swelling reverses at night

Skin folds-Absent

Appearance of Skin-Smooth,

Normal

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Swelling not reversible at

night

Skin folds-Absent

Appearance of skin-

Smooth, Normal

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Swelling not reversible at

night

Skin folds-Shallow

Appearance of skin-

Smooth, Normal

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Swelling not reversible at night

Skin folds-Shallow

Appearance of skin

- Irregular,

* Knobs, Nodules

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Swelling not reversible at

night

Skin folds-Deep

Appearance of skin –

Smooth or Irregular

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Swelling not reversible

at night

Skin folds-Absent,

Shallow, Deep

Appearance of skin

*Wart-like lesions on

foot or top of the toes

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Swelling not reversible at night

Skin folds-Deep

Appearance of skin-Irregular

Needs help for daily activities -

Walking, bathing, using

bathrooms, dependent on

family or health care systems

b) Chronic phase:

Hydrocele:

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Obstruction of lymphatics:

Distension & varicosities of l.v.

distal to obstruction.

Lymphatic edema.

Rupture of distended lymphatics.

Elephantiasis.

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Obstructive phase photos

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Clinical.

Microscopy

◦ Microfilariae in Giemsa stained thick blood films

Knott’s technique

◦ Microfilariae in chylous urine or hydrocele

Adults in lymph nodes

High eosinophilia

Serology - ICT

DEC Provocative test

Molecular techniques

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Imaging techniques:

1-Ultrasonography

2- Lymphoscintography

Calcification of inguinal lymph nodes

Obstruction of Cisterna

chyli or its tributeries

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Diethyl carbamazine (DEC): 6 mg/kg/day/12 days

(affects adults & mf). Repeated /6 months: till no mfmia.

Antihistaminics & corticosteroids.

Ivermectin: 150µg/kg body weight (Single oral dose).

Repeated /6 or 12 months (affects mf)

• Other treatment options are

– ivermectin

– combination of DEC and albendazole

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• Diethylcarbamazine (DEC) rapidly kills microfilariae and will

kill adult worms if given in full dosage over 3 weeks

• Release of antigens from dying microfilaria causes allergic-type

reactions – add an antihistamine and aspirin to treatment

regimen

Symptomatic treatment.

Surgical management.

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Prevention and control

• Rapid diagnosis and treatment of infected individuals

• Mass drug administration to at risk communities

• Vector control:

• eliminate mosquito breeding sites through improved

sanitation and enviromental management

• Personal protection against mosquito bites by

• insecticides,

• Bed nets and

• repellants

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Heartworms (Dirofilaria immitis)

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Heartworms (Dirofilaria immitis):

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Unsheathed

microfilaria in dog

blood -

DIAGNOSTIC

Adult male:

6-12 inches

long

Adult female:

12-16 inches

long

Adults coiled

in right side of

dog heart

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HUMAN INFECTIONS of Dirofilaria immitis are rare (~70 cases).

Larvae are killed by the host reaction and scar tissue nodules

form in lungs around worms

• Symptoms are coughing and chest pain.

In only 4 cases were adult worms recovered from the human heart.

These were found incidentally at autopsy and were not related to

the death of the patient.

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