Parasites

Question 1

Differences between protozoa and helminthes

Answer 1

Protozoa are unicellular parasites/eukaryotes that can transform from trophozoite (replicating form) to an inactive cyst form. Helmithes are multicellular parasites with their own organ and reproductive systems.

Question 2

Which stage of the protozoa is the resistant and infective stage?

Answer 2

the inactive cyst stage

Question 3

The protozoa can be broken down into 4 groups based on their organs of locomotion.

Answer 3

1) Amoebas: pseudopod locomotion -normally due to humans drinking sewage (i.e entamoeba histolytica)
2) Flagellates: flagella locomotion (i.e. Giardia, Trichomona vaginalis, Chagas disease)
3) Ciliates: Cilia locomotion
4) Sporozoans: no means of locomotion (i.e. Plasmodium)

Question 4

The helminthes can be broken down into 2 groups based on structure

Answer 4

1) Nematodes = Roundworms (free living or cause intestinal disease; i.e. hookworm, whipworm, and pinworm)
2) Cestodes = Tapeworms (flatworms acquired thru eating underprepared meat; i.e. pork tapeworm, beef tape worm, fish tapeworm.

Question 5

There are 4 plasmodium species that can cause malaria. Which is the most deadly, and which has this one replaced? Why has it replaced the old one?

Answer 5

Plasmodium falciperum is the deadliest and has repalced p. vivax. Plasmodium falciperum can infect all types of RBCs while p. vivax only likes young RBCs. Also, genetic changes (sickle cell and HbC trait, loss of Duffy Antigen) have made people in Africa less susceptible to p. vivax as before.

Question 6

Malaria has different phases (malaria paroxysm). Explain the cold stage, a hot stage and the sweating stage.

Answer 6

Cold Stage (abt an hr before rupturing of RBCs) -sensation of cold, shivering
Hot Stage (when RBCs burst & release merozoites) -fever, headachles, vomiting; seizures in young children
Sweating Stage (when merozoites infect other RBCs) -sweats, return to normal temp. followed by fatigue  

Total = a malarial attack last around 6-10 hours

Question 7

How is malaria transmitted?

Answer 7

transmitted to humans thru bite of an infected female mosquito of the genus Anopheles

Question 8

What is an impt feature of pathogenesis of p. falciuperum?

Answer 8

p. falciperum mature trophozoite and schizont can form to sequester in the deep venous vasculature b/c the infected RBCs can express PfEMPP-1 that can adhere to host molecules (CD36, ICAM-1) causing sequestration and other disease processes.

Question 9

In p. falciperum, the PfEMPP-1 can bind to host molecules and cause disease:

1) bind to CD36, and cause?
2) bind to ICAM-1, and cause?
3) bind to chondroitin sulfafe A (CSA), and cause?

Answer 9

1) PfEMPP-1 + CD36 = mediate sequestration of parasites b/c CD36 is found on monocytes, platelets, and microvascular endothelium
2) PfEMPP-1 + ICAM-1 = sequestration of infected RBCs in the cerebral microvasculature (cerebral malaria)
3) PfEMPP-1 + CSA = selective sequestration in placental tissue and role in malaria of pregnacny b/c placenta has CSA

Question 10

Babesia species (Babesia microti) is a bloodborne parasitic disease with an incubation period of 1-6 wks after transmission.

Explain the transmission and symptoms and what can this parasitic infection be confused for

Answer 10

Babesia microti is a zoonotic disease that is transmitted during the blood mael of an infected tick. The same tick that can transmit lyme disease (borrelia burgdorferi -spirochete). Symptoms are non-specific and consist of fatigue/weakness, shaking chills.

Question 11

Another bloodborne parasitic disease: Trypansoma Species. There’s an American Trypansomiasis causing Chaga’s Disease and an African Trypansomiasis causing Sleeping Sickness (via Tzetze fly). What is the causative agent of Chaga’s disease and what’s the vector?

Answer 11

T. cruzi is the causative agent of the American Trypanosoma species. It is transmitted by various species of bloodsucking traitomine or kissing (Reduvid) bugs when they contaminate breaks in skin, mucous membranes or conjunctivae with their FECES.

Question 12

What is the Romana sign?

Answer 12

when t. cruzi infects the skin or mucous membrane around a child’s eye causing fever and swelling around the area

Question 13

About 20-30% with Chagas disease will develop debilitating and sometimes life-threatening medical problems such as

Answer 13

heart rhythm abnormalities that can cause sudden death, a dilated heart that doesn’t pump blood well, a dilated eosphagus or colon leading to difficulties with eating or passing stool

Question 14

Another bloodborne parasitic pathogen is the leishmania species (infect neutrophils) causing leishmaniasis. What is the vector?

Answer 14

spread by bite of phlebotomine sand flies.

Question 15

What are the 3 different forms of leishmaniasis in people? (Americans with leishmaniasis most likely are coming back from abroad)

Answer 15

1) cutaneous leishmaniasis: skin sores that develop within weeks-months post-sand fly bite
2) visceral leishmaniasis: several internal organs particularly spleen, liver and bone marrow are affected and can be life threatening; will develop months (even years) post-sand fly bite
3) Mucosal leishmaniasis: LESS COMMON; Can be a sequela (consequence) of cutaneous leishmaniasis

Question 16

Giardiasis, caused by giardia lamblia is a flagellated enteric protozoan, is a common cause of endemic and epidemic diarrhea. It is the most commonly diagnosed enteric parasite in the U.S. How is it transmitted?

Answer 16

oral ingestion of Giardia CYSTS thru contaminated water or thru person-person or foodborne transmission.

Question 17

Giardiasis has an asymptomatic cyst passage, acute self-limited diarheea and a chronic syndrome of diarrhea, malabsorption and weight loss. How to diagnose it?

Answer 17

finding cysts in the stool or detection of the Giardia antigen in the stool

Question 18

After Giardiasis, what is the second most common parasitic infection in the United States? How is it transmitted?

Answer 18

Cryptosporidiosis by cryptosporidium parvum; transmitted by ingesting oocytes which are resistant to chlorination. Hence, recreational water (swimming pools, water parks) is one of the main risk factors for cryptosporidiosis.

Question 19

Symptoms of cryptosporidiosis

Answer 19

begin on avg 7 days after becoming infected with parasite, will have watery diarrhea for about 1-2 weeks in persons with healthy immune systems. It’s a diff story for immunocompromised ppl (i.e. HIV pts).

Question 20

Amebiasis, caused by entamoeba histolytica, is distributed worldwide. Explain transmission.

Answer 20

entamoeba histolytica is an invasive enteric protozoan parasite. Infection occurs when the cysts are ingested from contaminated water that has been contaminated with fecal matter.

Question 21

Explain the most common disease manifestation of amebiasis, caused by entamoeba histolytica and the more severe manifestation.

Answer 21

The most common disease manifestation is amebic diarrhea without dysentery. The disease can also cause pseudomembranous colitis and profuse bloody diarrhea. A more severe form of infection is an amebic liver abscess (more likely in the right lobe). This liver abscess can manifest acutely (with fever and RUQ tenderness and pain) or subacutely (with weight loss, abd pain, and less frequent fever)

Question 22

Trichomoniasis, caused by trichoma vaginales, is an extremely common infection in the U.S., and worldwide. T. vaginalis infections are commonly associated with

Answer 22

other STDs and are a marker of high-risk sexual behavior.

Question 23

Almost 50% of all women with T. vaginalis are asymptomatic and in men, the infection is usually asymptomatic. What are some symptoms that a symptomatic infected person can experience?

Answer 23

• vaginal discharge, pruritus, irritation
• frothy d/c similar to candidaisis and bacterial vaginosis.
• odor
• edema or erythema

Question 24

Intestinal Nematode: Ascariasis (ascaris lumbricoides) is th emost common helminthic infection of humans. The worms live and mate in the lumen of the small intestine. But there is no direct transmission between humans because

Answer 24

eggs need to mature in outside environment (i.e. soil) before becoming infectious, containing fully developed larvae)

Question 25

Explain transmission of ascaris lumbricoides causing ascariasis

Answer 25

1) ingest/inhale eggs
2) eggs hatch in small intestine and release larvae
3) larvae penetrate the intestinal wall and migrate via venous blood thru the liver to the heart, reaching lungs about 4 days after ingestion
4) they break into the alveoli and ascend the tracheobronical tree
5) then swalled and returned to the intestines where they develop into mature worms
* **adult worms can live approx 10-24 months.

Question 26

Most people with ascaris infections are asymptomatic. Only a small portion developes pulmonary symtpoms. However, what can happen, especially in children?

Answer 26

the worms tangle and cause obstruction, which can lead to perforation, intussusception, volvulus or death.

Question 27

Intestinal Nematode: Trichuris trichiura (Whipworm infection) is most common in poor rural communities with poor sanitary conditions. It is a soil transmitted helminth. Similar to ascarisis lumbricoides, the whipworm has no direct transmission. Explain. Also, what type of severe symptom can it cause?

Answer 27

Eggs are shed in stool where they undergo maturation. After ingestion the eggs hatch in the GI track and matures to an adult worm. Heavy infection can cause rectal prolapse, which can be recurring.

Question 28

Intestinal nematode: hookworm is a soil-transmitted helminth. What kinds of areas can hookworm infections (Ankylostomiasis) occur? What are the clinical implications?

Answer 28

Hookworm infections occur in areas where human feces are used as fertilizaer or where defecatin onto soil happens. People with hookworm infections have anemia (slowloss of blood), exhaustion and are always feeling tired.

Question 29

Intestinal nematode: hookworm is transmitted to humans via

Answer 29

the eggs mature in the environment and release rhabditiform larvae which penetrate the skin (usu. the bottom of the foot) and are carried thru blood vessels to the heart and then to the lungs, go up bronchotrachial tree and then swallowed to get to small intestine where they mature into adults.

Question 30

Intestinal nematode: Enterobiasis, caused by enterobiasis vermicularis (pinworm), is the most common worm infection in the U.S. Pinworm infections are most common in what age group?

Answer 30

in children so these infections are more likely to occur in families with school-aged children, in primary caregivers of infected children and in institutinalized children.

Question 31

How does one get infected with pinworm?

Answer 31

by ingesting pinworm eggs either directly or indirectly.

Question 32

How come people with pinworm infection have an itchy anal region? What test can be used to detect it?

Answer 32

b/c the worm deposits the eggs around the anus. The female worm while exiting the anus to deposit eggs can travel back thru genital tract and cause infections there. There’s a scotch tape test to put on anal region to see if you can catch the eggs.

Question 33

PInworm is super contagious unlike the others b/c they can do direct transmission because

Answer 33

their eggs are infective; no need to mature in outside environment.

Question 34

Intestinal cestode (TAPEWORMS OR FLATWORMS). What is the main cause of tapeworm infection?

Answer 34

eating undercooked meat (pork, beef, fish) from infected animals

Question 35

What are the 3 most commonly known tapeworm infections?

Answer 35

1) taneia saginata from beef
2) taneia solium from pork
3) diphyllobothrium latum from fish

Question 36

Tapeworm infections are generally uncommon in the U.S. b/c our grocery meats are pretty safe. The problem is with hunters. Why?

Answer 36

wild boar can be infected with taneia solium (pork tapeworm) and black bears can be infected with taneia saginata (beef tapeworm)

Question 37

Pork tapeworm (T. solium) can cause cysticercosis which can happen when infected person infect themselves.Cysticercosis can cause

Answer 37

problems in striated muscles as well as the brain, liver and other tissues. These cysts can cause serious sequellae if the localize in the brain resulting in neurocysticercosis.

Question 38

Eating raw fish, people should worry about which tapeworm

Answer 38

diphyllobothrium latum, which is also known as the fish or broad tapeworm = the largest tapeworm