Filariasis

 Introduction

Filariasis are vector borne human parasitic diseases with com-plex life cycle. They are caused by nematodes. In their mature stage they reside in lymphatic system or in connective tissues. Adult parasite itself can provoke inflammatory reactions in tissues. They produce large numbers of larvae called microfilariae .

Human Filarial Species

There are eight filarial species in which humans are the definitive hosts

Species Causing   LYMPHATIC FILARIASIS

Wuchereria bancrofti

Brugia malayi

Brugia timori

ONCHOCERCIASIS- RIVERBLINDESS

Onchocerca volvulus

EYE WORM DISEASE

Loa loa

OTHER SPECIES ( Generally considered to be non pathogens)

Mansonella  ozzardi       - causes pruritus

Mansonella perstans      - causes localized  angio edema and pruritus and neurological  symptoms

Mansonella streptocerca - cause pruritus, rash, hypopigmentation

Life Cycle of Human Filarial Worms

Adult Filarial Worms

·              Filarial worms are arthropod –transmitted parasites

 

·              They inhabit lymphatic subcutaneous and cutaneous tissues of humans

 

·              Adult male is smaller than females

 

·              Adults are sequestered in the tissues

 

·              All female worms produce primitive larvae called “microfi-lariae”

 

Microfilariae

·              These microfilariae are found in peripheral blood or in the skin

 

·              They relatively simple in their organization and structure

 

·              They are vermiform

 

·              In stained preparations they appear to be composed of a col-umn of nuclei

 

These nuclei are interrupted along their length by spaces and special cells

These cells are precursors of body organelles.

 

Some species of mf are enveloped in sheath others do not have sheath

 

Filarial Parasites                     Location                                 Disease

Wuchereria bancrofti                         Lymphatics                                       Elephantiasis

Brugia malayi                                   Lymphatics                             Elephantiasis

Brugia timori                                     Lymphatics                                       Elephantiasis

Loa Loa                                   EyeSubcutaneous                              Calabar Swelling

Onchocerca                                       Subcutaneous                          Onchocercomata

volvulus

Mansonella                                       Abdominal Cavity                            Mild Allergic

perstansReactions

Mansonella                                       Body Cavity

ozzardi

Mansonella                                       Subcutaneous Fat

streptocerca                             Subcutaneous

Lymphatic Filariasis

 

The following clinical manifestations may be seen

 

1.           Asymptomatic dsease

 

2.           Filarial fevers

 

3.           Chronic disease

 

4.           Tropical pulmonary eosinophilia

 

Asymptomatic Disease

 

·              Commonly seen in endemic areas

·              Frequently associated with Bancroftian and Brugian filariasis

·              Infected individuals never become symptomatic

·              Many chronically infected persons are amicrofilaraemic

 

Filarial Fevers: Initially

 

1.           Acute attacks of fever chills and malaise seen

 

2.           It lasts for 3-15 days each

 

3.           It is associated with retrograde adenolymphangitis

 

4.           This can occur several times a year

 

5.           Lymphadenitis affects commonly groin and axilla

 

6.           In men infected with W.bancrofti

 

a.           Lymph vessels of genitalia are affected

 

b.           This leads to funiculitis, architis, epididymitis

 

Chronic Disease

 

·              Occurs after 10-15 years of filarial fever (6months in non endemic persons)

 

·              Episodes of chronic obstructive disease due to damages to lymph vessels seen

 

·              Reversible lymphedema of legs, scrotum, arms, penes, or breasts present

 

§   This may progress to elephantiasis

 

·              Chyluria results from rupture of renal lymph vessels

 

·              Hydrocele is due to recurrent architis

 

Tropical Pulmonary Eosinophilia

 

·              It is a well recognized clinical entity in India and Singapore

 

·              It is attributed to occult filarial infection

 

·              It is characterized by paroxysmal nocturnal asthma and cough

 

·              It is associated with high eosinophilia

 

·              Can be relieved by DEC

 

·              There is high titer of antibodies to microfilariae

 

·              Microfilariae have been demonstrated in the lung

 

·              Small eosinophilic granulomas with mf are scattered throughout the lung

 

·              This condition may have resulted from altered host response to parasite, resulting in allergic phenomenon manifested by persistent hyper eosinophilia and pulmonary symptoms

 

Laboratory Diagnosis Of Filariasis

 

 

Specimens to be collected

 

1.           Blood : Nocturnal species/area – Night blood 10-12pm : Diurnal - Day time

 

2.           Chyluric urine:

 

3.           Exudate of lymph varix

 

4.           Hydrocele fluid

 

5.           Lymph node biopsy – not recommended for pure diagnostic purpose

 

6.           Ultrasound examination: shows characteristics filarial dance

 

Examination of blood and other body fluids

 

1.           By thick smear examination

 

2.           By thin smear examination Giemsa stained smears

 

3.           Saponin lysis and centrifugation- staining

 

4.           Knott concentration method

 

5.           Membrane filter concentration.

 

Demonstration of Components of the organisms

 

1.           Precipitation using antisera

 

2.           Counterimmuno Electrophoresis

 

3.           Elisa

 

4.           PCR

 

Demonstration of response to organisms

 

Responses include Non specific responses and Specific responses

 

Non specific responses

 

1. Filarial lymphangitis- must be differentiated from bacterial lymphangitis

2. Chronic lymphedema-

 

May also be caused by malignancy, renal and cardiac failure, post operative changes, congenital malformations

 

3. Architis and epidydymitis

 

In sexully transmitted diseases also these may be present

 

4. Tropical pulmonary eosinophilia

 

May be confused with Loeffler’s syndrome, Broncho pulmonary aspergillosis, eosinophilic pneumonia, drug reactions, other parasitic infections(Hook worms, Ascaris, Stongyloides).

 

Typical clinical history, exposure in appropriate areas, response to DEC will help with the diagnosis

 

Specific responses

 

1. Humoral immune responses

 

a. Antibody response

 

b. Hypersensitivity response

 

2. Cell mediated immune responses

 

a. CMI

 

b. CM hypersensitivity responses

 

Antibody responses

Antibodies can be detected by the following tests

 

In the past:

 

1. Gel diffusion

 

2. Complement fixation

 

3. Indirect immunofluorescence assays

 At present

4.      indirect haemagglutination test

 

5.           ELISA test