Download Filariasis

Soil transmitted nematodes
• Ascaris lumbricoides
• Trichuris trichiura
• Ancylostoma duodenale
• Necator americanus
• Strongyloides stercoralis
Soil-transmitted nematodes
Parasitic nematode of
human importance
Disease Lymphatic filariasis :
Agent Wucheraria bancrofti
Vector-borne nematode
Lymphatic disease
Elephantiasis
WHO elimination programme
• 8 species of filariae
parasitise humans
• Occur in a wide
range of habitats lymph glands, deep
connective tissue,
subcutaneous tissue
or mesenteries
• Intermediate host or
vector (insect)
• Adult worms
parasites of
vertebrate hosts
which produce
characteristic larvae
known as
microfilariae
Filarial nematodes
Filarial nematodes
• 3 of the species are primarily responsible
for most cases of human filariasis (Two
billion exposed and at least 200 million
infected)
– Wucheraria bancrofti (lymphatic)
– Brugia malayi (lymphatic)
– Onchocerca volvulus
(subcutaneous)
Wucheraria bancrofti
• Primary causative agent of lymphatic
filariasis
• Overt bancroftian filariasis : 115 million
cases worldwide (45.5 million India, 40
million subsaharan Africa)
• Widespread throughout the subtropics
and tropics (for e.g. Central Africa, India,
Thailand, Malaysia, Phillipines, Pacific
Islands, Haiti, coastal Brazil)
Different stages
of the Wucheraria
life cycle
Onchocerca volvulus : Onchocerciasis
• Periodic form : mf in
small numbers in
circulating blood
during the day and
peak density at night
(10 pm to 2 to 4 pm)
• Subperiodic form : mf
peak between noon
and 8 pm
• Periodic form
mosquitoes feed at
night ; subperiodic
form mosquitoes feed
during the day
Microfilarial
periodicity
Gold standard diagnosis using
blood films has diminished
relevance as mass drug
distribution expands
Use of sentinel sites for
ongoing night blood films
Diagnosis of Wucheraria
• Frequently made on clinical grounds in endemic
regions but demonstration of microfilariae in
circulating blood is key
• Where more than one species of filarial infection
occurs need well stained slides for morphological
identification of microfilariae
• Filarial infections can occur without
microfilaremia
Diagnosis : Wucheraria bancrofti
• Conventional method examination of thick
smear (stained)(counting chamber method)
• Concentration techniques (Nucleopore filtration
or Knott’s concentration)
• Detection of circulating filarial antigen immunochromatographic test (ICT)
• Serodiagnosis
• PCR-based assays for DNA
• Imaging studies (high frequency ultrasound,
lymphoscintigraphy)
– mf usually in blood
– 210-320um in
length
– Loose sheath
which when
stained with
Giemsa is pale
pinky blue and
does not stain well
– Nuclei are discrete
and tail ends taper
evenly
– No nuclei on the
tip of the tail
Characteristics of
mf of W. bancrofti
Symptomatology
• Clinical manifestations vary considerably
• Asymptomatic microfilaraemics show
microscopic hematuria and/or proteinuria
• Early signs : fever, lymphangitis (limbs,
breasts, scrotum), lymphadenitis (femoral,
inguinal, axillary and epitrochlear nodes)
• Orchitis, Lymphocoel, Hydrocoel
• Elephantiasis
Tropical pulmonary eosinophilia
(TPE)
• Distinct syndrome in some individuals
• Paroxysmal cough and wheezing
• Weight loss, low grade fever,
pronounced blood eosinophilia
• Total serum IgE and antifilarial Ab
titres raised
• Responds well to treatment but in its
absence progressive pulmonary
damage
Elephantiasis
• Relatively uncommon
and late complication
of filariasis
• Elephantiasis
(enlargement of
limbs, scrotum,
breasts or vulva with
dermal hypertrophy &
verrucous changes)
• Impairment of
circulation means
secondary bacterial &
fungal infections are
common
• Inflammatory changes
in the lymphatics
• Repeated attacks of
inflammation lead to
dilation & thickening
of the affected
lymphatics
(lymphedema)
• Chronic lymphedema :
hyperplasia of
connective tissue,
infiltration of plasma
cells, macrophages &
eosinophils
• Eventual thickening &
verrucous changes:
elephantiasis
Pathology
• Intensity and type
of host immune
response may
reflect range of
clinical
manifestations
• Immune response
varies by stage of
infection
Immunology
• Immunomodulatory
molecules
• Experimental
animal models (B.
malayi not W.
bancrofti)
Treatment
• Diethylcarbamazine (DEC) : an
effective microfilaricidal drug which
can eliminate adult worms more
slowly. Successfully administered in
table salt (Mass treatment)
• Combination of DEC & Albendazole
• Combination of DEC & Ivermectin
• Elephantiasis : surgery, rigorous
hygiene
Prevention and control
• Transmission depends upon two issues
(availability of vectors and presence of a
population of people to infect the vector)
• Vector control : larvicides, residual
spraying
• WHO programme to eliminate lymphatic
filariasis (GPELF) : 2 prongs - stop spread of
infection & reduce morbidity (mass treatment
once yearly for 4-6 yrs, education and intensive
local hygiene; GSK and Merck donation)
Case study : Mass drug
administration in India
• Mass treatment of 590 million people
• 1.4 billion doses of DEC and 0.51 billion
of Albendazole
• 1.1 million drug distributors
• Challenges : quality of DEC sometimes
poor, blister-packaging, side-effects,
treatment coverage variability (55-89% in
better developed states versus 0-35% in
less), monitoring and evaluation weak
Lymphatic filariasis elimination
programme in India: progress
and challenges
Kapa D. Ramaiah
Parasitology Today (2008) vol
25 (1) 7-8