Similar to the Trigger Word exercise, Mystery Questions are available for you to test your knowledge and aid your memorization efforts. Some of them use common associations found in standardized tests, and some use silly descriptions or associations to help you remember key features of certain organisms and syndromes. You will get the most out of these if you try to answer the question first before opening the answer.
Malaria/Babesia
Write down your answers. Then, self-check by clicking on the arrow .
Malaria (asexual human reservoir) and schistosomiasis (also filaria).
Fever without focal infection in an international traveler or immigrant, plus splenomegaly.
Plasmodium falciparum, gametocyte.
Hemolysis caused by intraerythrocytic parasites.
Primaquine/tafenoquine cause hemolysis in those with G6PD deficiency.
The deer tick carrying Babesia microti.
GI/GU Protozoa
Cysts are the infectious form of Giardia and Entamoeba histolytica rather than the trophozoites seen in active disease.
- Metronidazole.
- Tinidazole.
- E. histolytica.
- Echinococcus.
Dx by history, serology, and ultrasound.
Trichomonas (the most common sexually transmitted parasite).
- Definitive host carries the adult or sexual form of the parasite.
- Intermediate host carries the larval or asexual form of the parasite.
- Dead-end host doesn’t transmit the parasite to another host.
GI Helminths
Ascaris: A ball of worms can cause intestinal obstruction.
Hookworm (Ancylostoma or Necator species): It sucks blood from its attachment to the intestinal mucosa.
Pinworm (Enterobius): Adhesive tape is applied to the rectum to find eggs for diagnosis (also called “paddle test”).
Enterobius (pinworm): Note Strongyloides is passed in a larval form not an egg. Cryptosporidium is immediately infectious, but not a worm.
Strongyloides lives for many years by autoinfection in the same host. When hypermigration occurs, bacterial sepsis is one cause of fatality.
Dogs and cats: Animal hookworm species (Ancylostoma braziliense) cause “cutaneous larva migrans.”
Ancylostoma (hookworm), Strongyloides, and Schistosoma.
Diphyllobothrium is the main one to remember. There are others.
Diphyllobothrium latum (fish tapeworm) absorbs B12. B12 deficiency causes macrocytic anemia and neurologic problems.
The number of parasites in a host, the parasites tissue tropism (organs affected), the native pathogenicity of the parasite and the host immune state. Most patients with parasitic worm infections are asymptomatic unless there is a high parasite burden.
Tissue-Invasive Parasites
Cutaneous leishmaniasis—look for macrophages with intracellular amastigotes (oval protozoa with a small dot or bar-like kinetoplast).
Visceral leishmaniasis / Kala Azar (usually caused by L. donovani).
Ancylostoma/Necator (hookworm), Strongyloides, and Schistosoma.
Trichinella—meat inspection, laws that restrict feeding garbage to pigs, and public education have decreased its incidence.
- Sporozoa Group (e.g., malaria, Toxoplasma and Cryptosporidium).
- Some in Flagellate Group (e.g., Leishmania and Trypanosoma).
Toxoplasmosis is frequently asymptomatic in normal immune people. About 50% of the US population are infected but actual disease is rare.
Risk of ingesting Toxoplasma oocysts causing congenital toxoplasmosis. Toxoplasmosis risk especially kittens or undercooked meat (pork and lamb highest risk, with lower risk from beef or chicken).
Mostly brain and heart (also skeletal muscles, lung and liver).
- Tinea solium (neurocysticercosis). Man and pig are both intermediate hosts. The larval stage of Tinea solium (pig tapeworm) is the sole cause of cysticercosis. (Reminder: Does a pig’s foot have a sole or a solium?).
- Note that Toxoplasma causes seizures and ring-enhancing brain lesions, classic in HIV/AIDS, but this is a protozoa rather than a helminth.
Seizures from the larval stage of Tinea solium (neurocysticercosis) are caused by ingestion of the eggs from a human carrying the adult pork tapeworm, not from eating pig meat. Eating pig meat with cysticerci leads to adult tapeworms.
Tinea solium: Humans are the larval host in cysticercosis and can also carry the adult pork tapeworm. Most adult tapeworm infections are asymptomatic or cause only minimal GI upset.
- Schistosomiasis.
- S. haematobium presents with bloody urine.
- S. mansoni presents with portal hypertension, esophageal varices and ascites.
Schistosoma mansoni adults living in the pelvic and portal veins lay a lot of eggs over years, which shed into the portal system, are trapped in the liver and ultimately lead to fibrosis, portal hypertension and GI bleeding.
Schistosoma haematobium causes blood in a terminal urine sample.