Parasitic Diseases

Question 1

Helminth-Hookworm

Answer 1

1. Human nematode infection, may persist for many years in host
2. Acquired through skin exposure to larvae in soil contaminated by human feces
3. 3rd stage larvae capable of rapid penetration into skin, MCly feet
4. Itch at penetration, alveolitis w/ eosinophilia ensures
5. Larvae burrow into venules and embolize the lungs. Coughing brings larvae to mouth
6. Workup: microscopic stool exam for ova and parasites, CBC (confirm anemia)
7. Tx: albendazole or mebendazole - first line. Quarterly retreatment w/ improved anemia and malnutrition in 1 year

Question 2

Roundworm

Answer 2

1. Most cases are asymp – infected present w/ pulm and potentially severe GI issues
2. Predominates in areas of poor sanitation
3. Infection begins w/ ingestion of embryonated eggs in feces-contaminated soil, eggs hatch in SI and release small larvae that penetrate the intestinal wall. Larvae migrate to pulm vasc beds then to alveoli via portal veins (1-2 wks)
4. During pulm sxs, egges not being shed so dx via stool ova & para is NOT possible
5. Adult worms can live in gut 6-24 months and can cause bowel obstruction
6. High risk groups: international travelers, recent immigrants, refugees, international adoptees
7. Phases:
   • Early: 4-16 days after ingestion. Respiratory sxs – eosinophilic pneumo, fever, cough, dyspena, wheezing
   • Late: 6-8 wks after ingestion. GI effects – high load of parasites. Passage of worms
   
   8. Workup: CBC, sputum analysis, ascaris specific Ab, incr in IgE and IgG (later). Stool exam in established infection
   9. Tx:
      • Early – inhaled B-agonist, steroids (controversial)
      • Established – benzimidazoles

Question 3

Tapeworms:

Answer 3

1. Long, segmented worms
2. Worms lack intestinal tract and absorb nutrients thru integument
3. When humans primary host, limited to intestinal tract.
4. When humans are intermediate hosts, larvae within tissues migrating thru different organ systems
5. Cysticerci →MC in CNS and skeletal muscles
6. Remains asymp until cysts cause an mass effect on organ (can be 5-20 yrs after initial infestation)
7. Tx:
   • Intestinal Infestation: Praziquantel or niclosamide (Vit B12 in deficiency)
   • Cysticercosis: aysmp, no tx
   • Echinoccoccosis: Albendazole & sx OR Albendazole & PAIR (puncture, aspirate, inject, re-aspirate)

Question 4

Malaria:

Answer 4

1. Pts traveling from endemic areas (very rare)
2. Responsible for deaths of children in sub-Saharan Afric infected w/ P falciparum (MC cause)
3. Pts symptomatic a few wks after infection – H/A in all pts
4. Host’s previous exposure or immunity affects symptomology and incubation period
5. Classic paroxysm lasts for 1-2 hours and followed by a high fever
6. Workup:
   • Triad should prompt malaria smear: Thrombocytopenia, Elevated LDH, Atypical lymphocytes
7. Tx: Quinine sulfate, PLUS, Doxycycline (or clindamycin or pyrimethamine-sulfadoxine)

Question 5

Pinworm:

Answer 5

1. Prevalent in temperate regions
2. MC helinthic infection in the US
3. Resides in cecum, appendix, and ascending colon
4. Infection usually asymp, some have sharp prickling pains and intense anal pruritis (esp at night)
5. Transmission: direct contact w/ contaminated fomite
6. Workup: perianal cellophane swab (or tape) to detect eggs. Repeated exam in 1-2 days for more accuracy
7. Tx: Antihelmintics and improve hygiene
8. Reinfection is common (eggs remain in environment for 2 wks after deposition)

Question 6

Toxoplasmosis:

Answer 6

1. Marked depression in ration of suppressor T cells
2. MC sign = lymphadenopathy and fever
3. Infected during gestation – risk to fetus transplacentally or during delivery
4. Most significant manifestation: encephalomyelitis
5. May develop S&S and deficiencies later in life
6. Workup:
   • Direct detect - dx confirmed by T Gondii in blood, body fluid, or tissue
   • Indirect detect – IgG within 2 wks of infection using ELISA, skin test
7. Tx: usually unnecessary in asymp if >5 yrs
   • Pts w/ AIDS and CD4 <100 should be commences on suppressive therapy
   • Meds: Pyrimethamine (most effective) Leucovorin (prevents bone marrow suppression)

Question 7

Giardia:

Answer 7

1. MCly identified intestinal parasite in US and worldwide
2. Can cause asymp colonization or acute chronic diarrheal illness
3. Found in lakes, streams, ponds. Ingestion of 10 cysts sufficient to cause infection
4. Dx: cysts in stool via O&P, 3 specimens from 3 different days should be examined
5. Tx: Metronidazole is MCly Rxed. Fluid and lyte management is critical
   • Do not tx asymp ppl who excrete organism unless to prevent household transmission

Question 8

Crytosporidium:

Answer 8

1. Combined sewer outlets along the Merrimack (waterborne dz of our time)
2. Remain in bowel of immunocompetent individual for 1-2 wks but often indefeinitely if individual was immunocompromised
3. Increased incidence from stool of AIDS pts
4. Most pts present w/ nonspecific GI infection w/ severe diarrhea and abdominal cramps
5. 19 watery stools/day at peak of illenss
6. Most concerning is the microbe’s resistance to chlorination and filtration (d/t very small size)
7. Workup: PCR testing