The significance of Medical Parasitology

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Soil transmitted nematodes

• Ascaris lumbricoides
• Trichuris trichiura
• Ancylostoma duodenale
• Necator americanus
• Strongyloides stercoralis

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Soil-transmitted nematodes
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Parasitic nematode of human importance
Disease Lymphatic filariasis Agent Wucheraria
bancrofti Vector-borne nematode Lymphatic
disease Elephantiasis WHO elimination programme
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Filarial nematodes

• 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

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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)

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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)

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Different stages of the Wucheraria life cycle
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Onchocerca volvulus Onchocerciasis
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Microfilarial periodicity

• 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

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Gold standard diagnosis using blood films has
diminished relevance as mass drug distribution
expands

• Use of sentinel sites for ongoing night blood
  films

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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

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Diagnosis Wucheraria bancrofti

• Conventional method examination of thick smear
  (stained)(counting chamber method)
• Concentration techniques (Nucleopore filtration
  or Knotts concentration)
• Detection of circulating filarial antigen rapid
  format card test/ immunochromatographic card test
  (ICT)
• Serodiagnosis
• PCR-based assays for DNA
• Imaging studies (high frequency ultrasound,
  lymphoscintigraphy)

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Characteristics of mf of W. bancrofti

• 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

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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

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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

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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

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Early lymphedema
Advanced lymphedema
Hydrocoele
Elephantiasis
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Pathology

• 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

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Immunology

• Intensity and type of host immune response may
  reflect range of clinical manifestations
• Immune response varies by stage of infection

• Immunomodulatory molecules
• Experimental animal models (B. malayi not W.
  bancrofti)

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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

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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)

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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

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Lymphatic filariasis elimination programme in
India progress and challenges

• Kapa D. Ramaiah
• Parasitology Today (2008) vol 25 (1) 7-8