Parasitic Diseases - columbia.edu

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http://www.cumc.columbia.edu/dept/ps/2007/para/p1.pdf

 

 

Jonas Heymann

jjh2110

 

Parasitic Diseases

10-11 AM, Monday, November 8, 2004

Dr. Despommier

 

Lecture 1

1) Introduction to Parasitic Diseases

a) A definition: a parasite is any organism that takes metabolic

advantage of another

organism

i) Parasites take advantage of disruptions of normal flora

ii) Parasites take advantage of naïve immune systems

b) There are many different parasites

i) This course covers the following parasites:

(1) Protozoans

(2) Helminths (worms) include the following:

(a) Nematodes are non-segmented round worms

(i) Most nematodes are not parasitic

(ii) Almost 4 billion people harbor at least one species of parasitic

nematode

(iii)Many people harbor more than one species of nematode

(iv)In terms of disability adjusted life-years, Ascaris, Trichuris, and

hookworm cause more suffering than malaria, tuberculosis, and AIDS

combined according to the WHO

(v) Fecal-oral is the main route of nematode transmission

1. " Night soil " is a fertilizer used for growing fruits and vegetables

2. Animal species (other than humans) may become infected

(vi)Most helminths elicit TH2 protective immunity

(vii)Geohelminths include the following:

1. Enterobius vermicularis (pinworm)

2. Trichuris trichiura (whipworm)

3. Ascaris lumbrio-coides (giant intestinal worm)

4. Toxocara canis and Toxocara cati (visceral larva migrans)

(b) Cestodes are segmented flat worms

© Trematodes are non-segmented flat worms

(3) Arthropods

ii) This course does not cover the following parasites:

(1) Viruses

(2) Rickettsiae

(3) Bacteria

(4) Fungi

c) The lecture is organized as follows:

i) Morphology

ii) Life cycle

iii) Clinical disease

iv) Diagnosis

v) Treatment

vi) Prevention and control

2) Nematodes: Enterobius vermicularis, Trichuris trichiura, Ascaris

lumbrio-coides, Toxocara

canis, and Toxocara cati

a) Enterobius vermicularis (pinworm)

i) Morphology: the pinworm looks like a pin (slide 20)

ii) Life cycle

(1) Eggs are ingested

(2) Larvae hatch in the small intestine

(3) Larvae migrate to the colon

(4) Adults mature in the colon

(5) Gravid adults migrate out of the anus

(6) Adults lay eggs perianally

(7) Eggs embryonate perianally

(8) Eggs contaminate fingers

(9) Eggs are ingested

iii) Pinworm causes no clinical disease

iv) Eggs (slides 23 & 26) are identified on microscopic examination of

sticky tape that

has been applied perianally, although worms can be found in

histological sections of

tissues such as the appendix (slide 24)

v) Pinworm infection is treated with mebendazole which interferes with

egg production

by de-polymerizing all invertebrate tubulins (not vertebrate tubulins)

and is therefore

tolerated well

vi) Prevention and control of pinworm are difficult

b) Trichuris trichiura (whipworm)

i) Morphology: the whipworm looks like a whip (slides 30 & 31)

ii) Life cycle

(1) After a long incubation in soil, eggs are ingested

(2) Larvae hatch in the small intestine

(3) Larvae migrate to the colon

(4) Adults mature in the colon and produce prodigious numbers of eggs

(5) Unembryonated eggs pass out in feces

(6) Eggs, which can persist for long periods of time in harsh

conditions, embryonate

in soil

iii) Clinical Disease

(1) A high concentration of worms in the colon may lead to diarrhea

(2) A high concentration of worms in the colon may lead to

malnutrition and

anemia. Anemia may lead to PICA, heavy metal ingestion, neurological

deficits,

and further worm ingestion

(3) A high concentration of worms in the colon may cause fecal urgency

leading to

rectal prolapse (slide 35)

iv) Eggs (slide 37) are identified on microscopic examination of feces

v) Whipworm infection is treated with mebendazole

vi) Whipworm is prevented and controlled with sanitary disposal of feces

c) Ascaris lumbrio-coides (giant intestinal worm)

i) Morphology: the giant intestinal worm is very large (slide 43)

ii) The life cycle of the giant intestinal worm is complicated

(1) Eggs are ingested

(2) Larvae hatch in the small intestine, burrow through the intestinal

wall, enter the

bloodstream, and migrate to the liver where they feed on the hepatic

parenchyma

(3) Larvae migrate to the heart

(4) Larvae migrate into lung capillaries

(5) Larvae enter alveolar spaces

(6) Larvae migrate up the trachea and are swallowed

(7) Adults mature in the small intestine where they feed on the food

ingested by the

host and produce prodigious numbers (even more so than whipworm) of eggs

(8) Eggs pass out in feces and embryonate in soil where they can

persist for long

periods of time

iii) Clinical disease

(1) Light infections are asymptomatic as long as the adult worms do

not migrate

(2) Fever causes adult worms to migrate

(3) Heavy infections can have serious consequences

(a) Protein calorie malnutrition can cause failure-to-thrive

(b) A bolus of worms can cause bowel obstruction (slide 54) and allow for

proliferation of C. difficile

© Aberrant migration can lead to severe tissue damage

iv) Eggs (slide 58) are identified on microscopic examination of feces

v) Giant intestinal worm infection is treated with mebendazole

vi) Giant intestinal worm is prevented and controlled with sanitary

disposal of feces

d) Toxocara canis and Toxocara cati (visceral larva migrans)

i) Morphology: Toxocara does not have a distinct morphology (slide 63)

ii) The life cycle of Toxocara in cats and dogs is the same as that of

Ascarus in humans

iii) Clinical disease is nonspecific, but may include the following

(1) Fever

(2) Aberrant migration to the eye (slide 70) can migraine headaches,

loss of visual

acuity, or blindness

(3) Aberrant migration to the brain can lead to learning disabilities

iv) Because Toxocara does not produce eggs in humans, diagnosis is

based on serology

(ELISA)

v) Treatment

(1) Mebendazole interferes with egg production

(2) Prednisolone inhibits bystander activation

vi) Prevention and control includes the following:

(1) Sanitary disposal of dog and cat feces

(2) Periodic de-worming of pets

(3) Covering public sandboxes at night

e) It is interesting to note that most people of the world do not

suffer from (what we might

consider) common allergies, ulcerative colitis or Crohn's Disease.

Preliminary evidence

suggests that intestinal worms deflect the immune system away from

host tissues.