Introduction

Question 1

True/False: Parasites are microscopic organisms that live inside blood cells of the host. No other forms exist.

Answer 1

False. Parasites have a remarkable range of size and shape, ranging in size from cestodes over 30 feet in length to microscopic forms that are found inside human cells.

Question 2

Define Commensalism

Answer 2

one population (or individual) gains from the association and the other is neither harmed nor benefited.

Question 3

Define autoinfection

Answer 3

a reinfection in which the patient is his own best source of infection from a source already present in the body

Question 4

Define diarrhea

Answer 4

abnormal frequency and liquidity of fecal discharges.

Question 5

Define ectoparasite

Answer 5

a parasite that lives on the outside of the body of the host infestation

Question 6

Define eosinophilia

Answer 6

The formation and accumulation of an abnormally large number of eosinophils in the blood

Question 7

Define definitive host

Answer 7

the host which harbors the adult or sexually reproducing stages of a parasite

Question 8

Define intermediate host

Answer 8

that host which harbors the immature, larval, or asexually reproducing forms of the parasite

Question 9

Define reservoir host

Answer 9

an animal which replaces man as a host in the life cycle of a parasite

Question 10

Define mutualism

Answer 10

symbiosis in which both populations (or individuals) gain from the association and are unable to survive without it.

Question 11

Define parasitism

Answer 11

symbiosis in which one population (or individual) adversely affects the other, but cannot live without it. 2. infection or infestation with parasites

Question 12

Define symbiosis

Answer 12

in parasitology, the living together or close association of two dissimilar organisms, each of the organisms being known as a symbiont. The association may be beneficial to both (mutualism), beneficial to one without effect on the other (commensalism), beneficial to one and detrimental to the other (parasitism), detrimental to one without effect on the other (amensalism), or detrimental to both (synnecrosis).

Question 13

Define vector

Answer 13

a carrier, usually an arthropod, which transmits an infective agent from one host to another

Question 14

Define virulence

Answer 14

the degree of pathogenicity of a microorganism as indicated by the severity of the disease produced and its ability to invade the tissues of a host. It is measured experimentally by the median lethal dose (LD50) or median infective dose (ID50). By extension, the competence of any infectious agent to produce pathologic effects.

Question 15

Name three methods by which one may acquire a parasitic infection.

Answer 15

Ingestion of the parasite; Active penetration of the parasite; Injection by a vector

Question 16

True/False: All intestinal parasites have a similar life cycle. One swallows the egg, eggs hatch and the parasite lives in the intestinal tract.

Answer 16

False. Some parasite have a simple “hand-to-mouth” life cycle, but others must migrate through the body, notably lungs, to complete their life cycle.

Question 17

True/False: Young, healthy, adults (soldiers for example) are not at much risk of acquiring parasitic infections because they are in excellent physical condition and good general health.

Answer 17

False. Parasites can infect anyone who is exposed. Those victims who are physically debilitated or have poor immune systems may fare worse, but all can be infected when exposed.

Question 18

True/false: Diarrhea is a minor side effect of some parasitic infections, and can be ignored since it is self-limiting.

Answer 18

False. Diarrhea can lead to dehydration and fluids must be replaced. This can lead to debilitation and shock in extreme cases.

Question 19

Name some of the damaging effects a parasite can have on its host.

Answer 19

Blood loss, diarrhea and dehydration, they can trigger an immune response that can damage the host as well as defend against the parasite, tissue destruction (parasite eats your tissues), can make you feel poorly and lose appetite and lose nutrition indirectly.

Question 20

Which class of white blood cells may show increased numbers in parasitic infections?

Answer 20

Eosinophils

Question 21

True/False: Indirect evidence of parasitic infections obtained by serological testing is the best method of diagnosis.

Answer 21

False. Direct evidence is the best method. Direct evidence includes identification of a passed worm, microscopic examination of stool to identify parasite eggs or microscopic protozoa, etc.

Question 22

You have a patient who has a lab result showing a titer of 1:128. What does this mean in 1000 words or less?

Answer 22

The lab has made serial dilutions of the patient’s serum, and tested each dilution. The last dilution that showed a positive result was the tube containing serum diluted 128 times.

Question 23

What is the primary lab instrument used to diagnose parasitic infections?

Answer 23

A microscope, and a pair of really well-trained eyeballs. More technically impressive methods are used to supplement this basic starting point, but microscopy is really the foundation for this work.

Question 24

Why does the lab recommend obtaining multiple stool specimens over a period of days?

Answer 24

Some parasites tend to appear in the stool periodically in “showers”. For example, a specimen obtained on a Monday might not have any evidence, and by Wednesday the specimen is loaded with cysts of a parasite.

Question 25

True/False: Refrigeration will destroy parasites and should never be used for temporary storage of a specimen.

Answer 25

False. One can refrigerate a sample if it can’t be sent to the lab immediately (up to 48 hrs). Trophozoite motility will be lost, but the organisms will still be present, and can be identified.

Question 26

A patient complains of GI upset. You decide to order the following: Barium enema, prescription for Pepto-Bismol, cod liver oil, and an O&P exam. Does the sequencing of this series of item matter?

Answer 26

The lab would be grateful if you obtained the specimens for O&P first. The administration of oil, bismuth, barium, and antibiotics will make it impossible to identify parsites if present.

Question 27

How many microscopic fields should be examined when searching for parasites microscopically?

Answer 27

The lab won’t count the fields. They examine the entire 22mm square coverslip with overlapping fields so they see the entire sample.

Question 28

Why is it important to note your suspicions on the lab request when you order an O&P.

Answer 28

The lab will be alerted to your suspicions, and may have to use special techniques or precautions to process your request. For example, “R/O T.solium” (rule out Taenia solium [pork tapeworm]) would tell me you have information from the patient history, and I would want to be especially careful in handling this specimen. It would be helpful to clear the proglottids or stain them if any are recovered.

Question 29

What simple steps can everyone take to avoid infectious diseases, especially parasitic infections?

Answer 29

Wash your hands. Wash your food. Cook your food (well). Drink clean water. Avoid insect vectors. Dispose of human excrement properly.

Question 30

How many different types of specimen can you think of to submit for examination for parasites? Which one is the most common?

Answer 30

Stool is the most common. Blood, serum for serology, vaginal swabs, sputum, urine, CSF (rarely). This is a big hint. This means parasites must live in intestine, blood, vaginal tract, bladder, brain. You will need to learn to associate which organisms live in which tissue.

Question 31

What do you think would be the specimen of choice for an intestinal lumen-dwelling parasite?

Answer 31

Stool, request exam for O&P.

Question 32

Describe the collection technique of lumen-dewlling parasites.

Answer 32

Provide feces only, no tissue, no water, no urine, no breakable jars or glass, put only feces in the container.. Patient may defecate directly into a stool cup (ice-cream carton style container). Portions are stirred into vials of PVA (polyvinyl alcohol preservative) and 10% formalin (another preservative).

Question 33

The laboratory returns a report annotated “NPF” or “NPS”. What does this mean? Is this a negative result?

Answer 33

No Parasites Found, or No Parasites Seen. We looked, but didn’t find anything. This is not the same as negative. The second sample submitted may yield a lot! Some parasites are passed in “showers”.

Question 34

What is the best source of information for serological testing available to you atyour current location?

Answer 34

Call the lab officer and ask.

Question 35

Why is it important to wash your hands?

Answer 35

Clinicians are in a position to spread microbes from patient to patient very easily. CDC data indicates that there are 90,000 deaths recorded annually that could be prevented by handwashing. Don’t add to that number.

Question 36

Name ways a parasite may cause damage to the human host.

Answer 36

Parasites can cause: tissue damage blood loss vigorous immune response that damages host tissue secondary bacterial infections discomfort death probably many more items may be listed.

Question 37

How does a human host acquire a parasitic infection?

Answer 37

Ingestion Injection Direct penetration

Question 38

Is it appropriate to freeze a stool specimen to preserve it until it can be examined?

Answer 38

No. You can refrigerate stool if delivery to the lab will be delayed.

Question 39

Which part of the stoolspecimen is of most interest to the lab?

Answer 39

The really ugly bits. The nice, smooth, peanut butter consistency material may not yield much. Bloody, mucoid, nasty looking stool is where one will find parasites.

Question 40

What can be done to prevent the spread of parasitic disease?

Answer 40

Wash your hands. Wash your food. Cook your food. Drink clean water. Avoid insect vectors. Properly dispose of excrement. None of this is easily accomplished when you deploy.

Question 41

Are our troops currently deployed to any areas that might have any parasitic diseases? Where? What diseases? Could you diagnose these items? What test(s) might be available to you? What drugs?

Answer 41

Afghanistan and Iraq both have several parasitic disease problems. Big hint. Try using the CDC yellow book and look up information about these areas and see what you can learn.