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Ascaris.ppt
 

Ascaris.ppt

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    Ascaris.ppt Ascaris.ppt Presentation Transcript

    • Case History
      • 6-year-old daughter of seasonal farm worker
      • Presents with malnourishment, abdominal swelling, cough, wheeze and fever
      • CXR reveals a lobar pneumonia
      • X-rays Plain Abdomen revealed suspicion of worms
      • Admitted for initial antibiotic therapy
      • After 2 days of antibiotics, a worm is found in her bed
      • Stool exam reveals …
      • No mucous
      • No pus cells
      • No RBCs
      • But…
    • Ascaris lumbricoides Dr Kamran Afzal Classified Microbiologist
    • Nematode
      • The intestinal nematodes
        • Ascaris
        • Hook worms
        • Pin worm
        • Whip worm
      • The blood- and tissue dwelling nematodes
        • Filaria
        • Trichinella
    • Prevalence of Helminths
    • Family Ascaridae
      • Two species, one in humans and the other in pigs
      • Ascaris lumbricoides - humans
      • Because of size and cosmopolitan distribution, these are well known parasites
      • Rural > urban
      • Children > adults
    • Prevalence
      • Most common helminthic human infection - Worldwide
      • High prevalence in underdeveloped countries that have poor sanitation
      • Occurs during rainy months, tropical and subtropical countries
      • Largest nematode to infect the human intestine
      • A common cream colored roundworm that is parasitic in the intestines of humans
      • An estimated 1 billion people are infected
        • 1 out of 4 people in the world
    • Epidemiology
      • Indiscriminate defecation particularly near areas of habitation seeds the soil with eggs
      • Children become infected by ingesting soil or putting soiled items in the mouth
      • The eggs may contaminate unwashed vegetables and water supplies
      • Eggs can be carried by cockroaches, flies, wind, and even on money
    • Morphology of Eggs
      • Fertilized egg
      • mammillated
      • thick external layer
      • unembryonated
      • measures 55-75 X 35-50 mm
      Albuminous layer Egg shell Ovum
      • Un-fertilized egg
      • elongated and larger than fertilized egg
      • thin shelled
      • shell ranges from irregular mammillations to a relatively smooth layer completely lacking mammillations
      • measures between 85-95 X 43-47 mm
    • Characteristics of Eggs
      • Eggs can survive for prolonged periods as long as warm, shade, moist conditions are available
      • Eggs are resistant to low temperatures, desiccation, and strong chemicals
        • Can remain viable for up to 10 years
      • Eggs are resistant to usual methods of chemical water purification, removed by filtration and killed by boiling
      • Eggs can embryonate in solutions of formalin, H 2 SO 4 and HCl
      • Eggs embryonate but do not hatch until ingested by man
      • Developing larvae are destroyed by sunlight, high temperatures and desiccation
    • Morphology of Worms
      • Adult worm
      • Tapered ends; length 15 to 35 cm
      • Characterized by three large rounded lips
      • Female is larger in size and has a genital girdle
      • Ovaries are extensive, contain up to 27 million eggs at a given time
      • Female lays eggs into host intestine
        • 200,000 per day passed out in host feces
      • Feed on semi-digested contents in the gut
      • Evidence shows that they can bite the intestinal mucus membrane and feed on blood and tissue fluids
    • A pair of female and male worms Notice the vulvar waist (arrow) of the female worm and the coiled end of the male worm
    • Modes of Transmission
      • Definitive host
        • Humans or pigs
      • Intermediate Host
        • None
      • Mainly via ingestion of water or food (raw vegetables or fruit in particular) contaminated with A. lumbricoides eggs
      • Children playing in contaminated soil may acquire the parasite from their hands
      • Occasionally by inhalation of contaminated dust
      • Transmission can also occur via placenta
    • Life Cycle
    • Life Cycle - Descriptive
      • Females lay eggs in small intestine -> feces
      • After 14 days, L1 filariform larvae develop in eggs
      • Ingestion of raw fruits or vegetables contaminated with eggs
      • When ingested, larvae escape by way of operculum (eggs hatch) in small intestine, - L2 rhabditiform larvae
      • L2 penetrate/burrow through the intestinal wall, enter portal blood stream, migrate to liver, heart or lungs in 1-7 days
      • From lungs, they are coughed up and swallowed
      • Reach the small intestine
      • Moult twice to become L4 larvae
      • Mature and mate, and complete their life cycle
    • Pathology
      • Migration of larvae
      • Little damage is caused by the penetration
      • Some larvae migrate to ectopic sites and dependent upon number and location, cause various inflammatory responses, leading to very severe allergic reactions
        • Spleen, liver, lymph nodes and brain
      • Transplacental migration can also occur
      • In the lungs
      • Worms destroy capillaries in the lungs, causing hemorrhage
      • Heavy infections can lead to pools of blood which block air sacs
      • Migration of white blood cells lead to more congestion; a condition known as Ascaris pneumonitis
        • Loeffler's pneumonia
      • Lung tissue destroyed and bacterial infections occur, may be fatal
    • How the worms cause Pathology
      • Normal worm activities - Rob the host of nutrients
      • Overcrowding leads to wandering
        • Females wander in search of males
      • If worms migrate to stomach, acid irritates them leading to nausea, abdominal pain, restlessness and allergic reactions
      • Penetration of the intestine or appendix can lead to peritonitis which is often fatal
      • Aspiration of a vomited worm can result in death
      • If worms migrate to lungs, they can cause extensive damage and possible death
    • Symptoms
      • Symptoms associated with larval migration
      • Migration of larvae in lungs may cause hemorrhagic/ eosinophilic pneumonia, cough (Loeffler's Syndrome)
      • Breathing difficulties and fever
      • Complications caused by parasite proteins that are highly allergenic - asthmatic attacks, pulmonary infiltration and urticaria (hives )
      • Symptoms associated with adult parasite in the intestine
      • Usually asymptomatic (85%)
      • Vague abdominal discomfort, nausea in mild cases
      • Malnutrition in host especially in children in severe cases
      • Heavy worm loads can retard physical and mental development
      • Sometimes fatality may occur when mass of worms cause intestinal obstruction
      • Symptoms associated with worm migration
      • Worms retain motility, do not attach
      • Migration of adult worms may cause signs and symptoms of perforation, peritonitis, appendicitis or extrahepatic biliary obstruction
      • Severe inflammatory reactions mark the migratory route
      • Dermatological and allergic reactions can occur
    • Host immune response
      • Innate Immune Response
      • Macrophages, neutrophils and most importantly eosinophils
      • The worms would be coated with IgG or IgE which would increase the release of eosinophil granules
      • Adaptive Immune Response
      • High IL-4 production, high levels of IgE, eosinophilia and mastocytosis
      • Prior infection does not confer protective immunity
    • Complications
      • Intestinal obstruction, volvulus, intussusception
      • Obstruction of intrahepatic and extrahepatic bile ducts
      • Peritonitis caused by intestinal perforation
      • Chronic pancreatitis
      • Acute or chronic appendicitis
      • Pneumonitis, bronchitis and asthma
    • Emergence of adult worms A large mass of Ascaris lumbricoides that was passed from the intestinal tract
    • Intestinal blockage in heavy infections - intestinal obstruction Worms may knot up causing blockage which may be fatal
    • CS of a liver specimen contains many adult worms of A.lumbricoides obstructing the intrahepatic and extrahepatic bile ducts A.lumbricoides in common bile duct
    • An autopsy specimen shows intestinal obstruction by many adult worms of A.lumbricoides Markedly distended intestinal loop and worms protruding from the perforated wound
    • Peritonitis caused by intestinal perforation due to Ascaris Resected bowel and the adult female from the peritoneal cavity
    • Penetrate to the pancreas and the appendix
    • Ascarid chronic pancreatitis
    • Larva in section of lung Ascaris Pneumonitis Asthma
    •  
    • Laboratory Diagnosis
      • Macroscopic identification
        • Of adults passed in stool or through the mouth or nose
      • Larval worms
        • Detection in sputum
      • Stool Microscopy
        • Eggs may be identified on direct stool examination
      • Eosinophilia
        • Eosinophilia can be found, particularly during larval migration through the lungs
      • Imaging
        • In heavily infested individuals, particularly children, large collections of worms may be detectable on plain film of the abdomen
      • Ultrasound
        • Ultrasound exams can help to diagnose hepatobiliary or pancreatic ascariasis
        • Single worms, bundles of worms, or pseudotumor-like appearance
        • Individual body segments of worms may be seen
      • Endoscopic Retrograde Cholangiopancreatography (ERCP)
        • A duodenoscope with a snare to extract the worm out of the patient
    • Treatment
      • Albendazole
        • A single oral dose of 400 mg
      • Mebenazole
        • 100 mg orally twice daily for 3 days
      • Piperazine
      • Pyrantel pamoate
      • Ivermectin
      • Levamisole
    • Prevention
      • Good hygiene is the best preventive measure
      • Avoid contacting soil that may be contaminated with human feces
      • Wash hands with soap and water before handling food
      • When traveling to areas where sanitation and hygiene are poor, avoid water or food that may be contaminated
      • Wash, peel or cook all raw vegetables and fruits before eating
      • Dispose of diapers properly
      • Prevention of reinfection poses a substantial problem since this parasite is abundant in soil
        • Good sanitation is needed to prevent fecal contamination of soil
    • Control
      • Periodic mass treatment of children with single doses of mebendazole or albendazole
        • Helps reduce transmission in community but does not protect from reinfection
      • Environmental sanitation
      • Limit using human feces as fertilizer
      • Health education
    • How many people in the world are estimated to be infected with A. lumbricoides ?
    • Who are the definitive host/s of this parasite?
    • Name 2 modes of transmission?
    • What morphological difference can be seen in fertile and infertile eggs?
    • Name the symptoms caused by larvae migration in the lungs
    • What is the drug of choice for this parasite?
    • What are some of the methods of prevention?