(3/9) Jaki Lecture: Parasitic Infections Parasites in general

- Parasites are organisms that cannot live independently, they obtain food and shelter by living on or within another organism. Parasites do not always need a vector, but they always need a host. Here are definitions

o Definite host: Hosts the parasite in the adult and sexual stage o Intermediate Host: Host the parasite in the larval and asexual stage o Vector: An organism (usually an insect), that is responsible for transmitting the infection

- Types: o Internal Parasites: Protozoa, Helminths o External Parasites: Arthropods/invertebrate animal with exoskeleton

- Treatment options are very limited, and vaccines are not efficacious. By the time the immune system recognizes a parasite, it has been well-established and multiplied sufficiently to stay.

Amebiasis – Entamoeba histolytica [Intestinal Protozoan Parasite] - Characteristics: Resembles a piece of chewing gum - Transmission: Drinking water or food with poor hygiene - Pathology: A GI disease that can develop into a severe extra-intestinal

disease, at which point the risk of mortality becomes significant. Trophozoite may cross into the bloodstream and infect the liver, lung, or brain, causing Hepatitis, Pneumonia, and Meningitis, respectively.

o Acute Amebiasis (Intestines): Includes abdominal pain, frequent blood stools, and a low fever o Chronic Amebiasis (Extra-intestinal): Recurrent blood and mucois dysentery, also affecting other organs

such as liver, lung, and brain - Prevention: Better hygiene and efficient sewage treatment – stop fertilizing fields with sewage - Treatment

o à Metronidazole is the preferred agent. It is an imidazole derivative used to treat Acute and Chronic § MoA: 5-Nitro group gets reduced to a reactive intermediate that binds parasitic DNA

o à Iodoquinol is another agent used however it is ineffective in extra-intestinal (chronic) disease Giardiasis – Giardia lamblia [Intestinal Protozoan Parasite]

- Characteristics: Looks like an old ‘hippi’ man with a flagellate - Transmission: Drinking contaminated water

o Acquired by traveling to endemic areas (Russia, India, Rocky mountains) or daycare centers

- Pathology: Beavers act as ‘reservoir’ hosts – as they are not essential for the giardia life cycle. Beavers poop it out, the stream is the vector, humans consume and act as host for giardia to multiple within. The cysts are the transmission element, trophozoites initiate the infection in the small intestine, and the sporozoids do the damage in the lower intestine upon the GI wall

o Acute Giardiasis: Abdominal pain and frequent diarrhea. No blood or fever. o Chronic Giardiasis: Abdominal pain and frequent diarrhea. No blood or fever. Some absorption issues

- Prevention: Better hygiene and efficient sewage treatment - Treatment

o à Metronidazole is the preferred agent o à Iodoquinol is effective

Trichomoniasis – Trichomonas vaginalis [Luminal Protozoan Parasite] - Characteristics: A frequent worldwide flagellate - Transmission: STD associated with poor hygiene - Pathology: Trichomonas does not have a vector and does not encyst. Organism requires pH > 5.9 to grow

o Infected Women: Often asymptomatic, though may experience mild to severe vaginitis in the case of heavy infections. It is best distinguished by the foul-smelling discharge.

o Infected Men: Often asymptomatic, occasionally some mild urethritis and/or prostatitis o Complications: Women are more susceptible to HIV if comorbid Trichomoniasis. Additionally,

trichomonas infected women may have premature or low-birth-weight babies - Prevention: Condoms - Treatment

o à Vinegar douche – this is acidic and will decrease the pH. It is first-line treatment o à Metronidazole

Vector Food/water Host àHuman Reservoir n/a Cysts Yes.

Vector Water Host àHuman Reservoir Beaver Cysts Yes.

Vector No. Host àHuman Reservoir n/a Cysts No.

Toxicoplasmosis – Toxoplasma gondii [Blood Protozoan Parasite] - Characteristics: - Transmission: Consume infected meat or exposure to cat reservoir - Pathology: Farm animals carry the etiologic agent in their muscle tissue. Outdoor cats may

acquire the parasite through intermediates like birds or mice. In the cat small intestine, de-cystation will promote development of gametocytes, which fertilize and develop into oocysts, which release sporozoites into cat litter and cat fur. Then humans get infected.

o General Symptoms: Infection is frequent, though there rarely are Sx o Pregnancy: Significant risk to the fetus in concurrent toxicoplasmosis. 5-10% miscarriage, and ~10%

serious brain and eye damage to the fetus. o Immunocompromised: Generalized parasitemia involving multiple organs and often death

- Prevention: Pregnant women should avoid cat litter and not handle uncooked or undercooked meat - Treatment:

o à Pyrimethamine (Antifolate) o à Sulphadiazine (Enzyme inhibitor) – often given in combination with pyremethamine o à Spiramycin (Macrolide Abx): An experimental compound only given in severe cases in pregnancy

§ Using an ultrasound, we can determine if a baby is infecting by checking the spleen size. § Pregnant w/ toxoplasmosis but baby isn’t affected à Spiramycin (reduces likelihood) § Pregnant w/ toxoplasmosis and baby is affected à Pyrimethamine + Sulfadiazine (extreme cases)

Elephantiasis – Wuchereria bancrofti [Helminth Parasitic Worm] - Characteristics: A parasitic roundworm (nematode), males 3-4cm and

females 8-10cm --- huge. - Transmission: Mosquito deposit of microfilaria/larva during bloodmeal - Pathology: Following infection, the male and female worms migrate to and form a ‘nest’ in the human lymphatic

system. Maturation into larger worms that intertwine will block the lymphatic system. This usually occurs early during childhood and is asymptomatic until later in life whereupon lymphedema becomes significant.

o Genera Symptoms: Lymphoedema of the limbs, genital disease including swelling of the scrotum and penis. Subclinical lymphatic damage results in significant kidney damage with proteinuria and hematuria

o Asymptomatic phase: Usually during childhood. Worms mature, filariae run around o Inflammatory (Acute) phase: Immune system starts kicking in, the human begins to notice the infection,

edema and pain are the primary symptoms o Obstructive (Chronic) Phase: Clinical elephantiasis sets in. Thickening of skin, damage to lymphs

- Treatment o à Ivermectin – A new drug used to treat filariasis, winning the Nobel Prize 2015 for Campbell & Omura.

This drug has several conjugated lactone rings forming the macrocyclic lactone. Must treat patents early with it before permanent damage is done to the lymphatic system

Note: I did not consult or look at the ‘study guides’ posted by Jaki or Glowacki prior to making this. Check ‘em out

Vector Cat Host àHuman Reservoir Mice Cysts Yes.

Vector Mosquito Host àHuman Reservoir None. Cysts Larval