INTESTINAL NEMATODES I

Question 1

State two morphological features of Nematodes.

Answer 1

• Aka nemahelminthes.
• Are roundworms with a cylindrical body.
• Have a complete digestive tract including a mouth and an anus.
• Body is covered with a non cellular, highly resistant coating called cuticle.
• Have separate sexes , males have coiled tails while females are larger than the males.

Question 2

List major examples of intestinal nematodes.

Answer 2

• Enterobius vermicularis
• Trichuris trichiura
• Ascaris lumbricoides
• Necator americanus
• Ancylostoma duodenale
• Strongyloides stercoralis
• Trichinella spiralis

Question 3

Describe how one would distinguish the different eggs of Ascaris lumbricoides.

Answer 3

• Fertilized eggs - are oval, transparent, segmented, may be mamillated or decorticated.
• Unfertilized eggs - are longer, narrower, may also be mamillated or decorticated.
• Embryonated eggs - have visible larva inside.

Question 4

Briefly discuss the life cycle of Ascaris lumbricoides.

Answer 4

• Humans acquire the infection after ingesting food or water contaminated with human feces containing infective eggs of Ascaris lumbricoides.
• The larvae hatch in the small intestine, penetrate the intestinal mucosa , and migrate through the gut wall into the bloodstream where they are transported in the circulatory system and eventually lodged in the lung capillaries.
• They penetrate the alveoli and migrate from the bronchioles to the trachea where they are coughed out as sputum and are swallowed into the pharynx, back into the small intestines where they mature into adults.
• The adult worms live in the lumen of the SI and mate , after which females release about 200,000 eggs per day , which are passed out in the feces.
• Fertile eggs embryonate and become infective after 18 days and if ingested , the cycle continues.

Question 5

List down 5 antihelminthic drugs that are effective in the treatment of Ascariasis.

Answer 5

• Albendazole
• Mebendazole
• Ivermectin
• Piperazine
• Levamisole
• Pyrantel Pamoate

Question 6

Distinguish between filariform larvae and rhabditiform larvae.

Answer 6

• Rhabditiform larvae are 1st and 2nd stage larvae while filariform larvae are 3rd stage larvae.
• Rhabditiform larvae are feeding forms while filariform larvae are non feeding forms.
• Rhabditiform larvae are non infectious while filariform larvae are infectious forms.

Question 7

Host defenses against helminths are stimulated by ?

Answer 7

Interleukins synthesized by the Th-2 subset of helper T cells.

Question 8

What causes eosinophilia ( striking increase in no. of eosinophils) in nematode infections ?

Answer 8

The no. of eosinophils is increased by Interleukin -5 .

Question 9

What stimulates the production of Interleukin- 5 that causes eosinophilia?

Answer 9

Cysteine proteases produced by the worms to facilitate their migration through human tissues are the ones that stimulate production of IL- 5.

Question 10

Eosinophils produced do not ingest the parasitic organism , what do they do instead?

Answer 10

The eosinophils attach to the surface of the parasite via IgE , and secrete cytotoxic enzymes contained within their eosinophilic granules.

Question 11

What promotes production of IgE , that enables eosinophils to attach onto the surface of the parasite?

Answer 11

Production of IgE is increased by Interleukin-4.

Question 12

State some of the major manifestations of Ascariasis infection caused by Ascaris lumbricoides.

Answer 12

Abdominal pain and discomfort - caused by presence of the worms in the small intestines which may result in mechanical obstruction of the intestines, bile and pancreatic ducts.

Ascaris Pneumonia - Pneumonitis is caused by larvae migrating through the lungs which may induce an inflammatory response.

Other respiratory symptoms may include: dry cough , difficulty in breathing and eosinophilia.

Malnourishment and growth impairment in children - because the adult worms derive nourishment from ingested food in the small intestines.

Question 13

State some of the signs and symptoms that constitute Loeffler’s Syndrome in Ascariasis.

Answer 13

Bronchial spasms

Mucus production

Dry cough

Eosinophilia

Pulmonary infiltrates

Fever

Difficulty in breathing ( wheezing )

Question 14

Means of diagnosing a patient with Ascariasis?

Answer 14

Adult worms may be observed macroscopically in the stool.

The eggs can also be detected microscopically in the stool . A concentration procedure may be required since the eggs are difficult to detect if the infection is light.

Question 15

State the habitat of Ascaris lumbricoides in human hosts.

Answer 15

Lives in the lumen of the small intestines.

Question 16

Outline some of the preventive measures that can be used in the control of Ascaris lumbricoides.

Answer 16

Wash your hand with soap and warm water after using the washrooms and before handling food.

Wash, peel or cook all raw fruits and vegetables before eating them , especially those that have been grown on soil fertilized with human waste as manure.

Proper disposal of faeces and sewage to avoid contamination.

Avoid using untreated human faeces as manure for growing crops as this contaminates the soil.

Treatment of infected individuals with antihelminthic drugs such as albendazole.

Health education - teaching children and communities on the importance of hygienic practices such as washing hands , and proper disposal of human waste in toilets and pit latrines.

Question 17

State one way in which Pig Ascaris species are different from the Ascaris species that infect humans.

Answer 17

In pig Ascaris - the teeth are typically triangular in shape while in human Ascaris species, the teeth have concave sides .

Question 18

List some of the serious complications that may arise as a result of Ascariasis.

Answer 18

• Intestinal obstruction.
• Biliary tract obstruction - which may present with jaundice.
• Invasion of liver and spleen - may lead to liver and splenic abscess.
• Pancreatitis.
• Appendicitis - if the appendix is affected.
• Intestinal perforation which may lead to peritonitis.
• Asphyxia - during larval migration in the lungs.
• Pneumonitis.
• Volvulus in the intestines.
• Protein energy malnutrition - because the parasite feeds on ingested food in the intestines.

Question 19

Common name for Enterobius vermicularis?

Answer 19

Pinworm

Question 20

How would you distinguish between the adult female and the adult male worms of Enterobius vermicularis?

Answer 20

• Adult female is thicker and longer compared to the adult male.
• Adult female has a long , slender and pointed posterior end while the adult male has a curved posterior end carrying a single copulatory spicule .

Question 21

State the site of infection of the Enterobius vermicularis worms.

Answer 21

The lumen of the cecum and colon .

Question 22

State some of the major ways in which infection by Enterobius vermicularis can spread.

Answer 22

• Self infection occurs by transferring infective eggs from anus to the mouth, by touching the mouth or handling food with hands that have scratched the perianal area. The eggs are highly infectious within hours of being laid.
• Person to person transmission - occurs through handling of contaminated clothes or bed linens .
• Enterobiasis may also be acquired through surfaces in the environment that have been contaminated with pinworm eggs e.g curtains and carpets.
• A few eggs may also become airborne and are inhaled then swallowed, following the same developmental pattern as ingested eggs.

Question 23

Briefly discuss the life cycle of the Enterobius vermicularis worm.

Answer 23

• Following ingestion of the infective eggs, the larvae of Enterobius vermicularis hatch in the small intestines and differentiate into adults.
• The adults migrate into the colon where they establish themselves and mate with the adult females.
• The gravid female worms migrate nocturnally outside the anus and oviposit while crawling on the skin of the perianal area.
• The eggs are deposited by the females on the perianal folds.
• The larvae contained inside the eggs develop and the eggs become infective in 4-6 hours under optimal conditions. Within 6 hours, the eggs develop into embryonated eggs and become infectious.
• Self infection occurs by transferring the infective eggs to the mouth, or ingesting food that has been handled by hands that have scratched the perianal area.

Question 24

Time interval from ingestion of infective eggs of Enterobius vermicularis to oviposition by the adult females is ?

Answer 24

About 1 month

Question 25

Lifespan of the adult Enterobius vermicularis worm?

Answer 25

About 2 months.

Question 26

List down some of the major clinical manifestations of Enterobiasis caused by infection by Enterobius vermicularis worms.

Answer 26

• Perianal pruritus - itchy anal region , especially at night. This is caused by a hypersensitivity/ allergic reaction either to the proteins of the adult females or to the eggs laid by the female worms around the perianal region . The worms migrate from the colon at night.
• Irritability and fatigue can also occur from loss of sleep .
• Teeth grinding and insomnia due to disturbed sleep.
• Abdominal pain and appendicitis can also be reported.
• When the infection is heavy , there can be a secondary bacterial infection due to the irritation and scratching of the perianal area.
• The female genital tract may also be infected.

Question 27

List some of the medications that are effective in the management of Enterobiasis.

Answer 27

• Mebendazole
• Albendazole
• Pyrantel Pamoate
• These drugs kill the adult worms in the colon , but not the eggs , hence retreatment in 2 weeks is necessary since reinfection is very common. Household members should also be treated .

Question 28

Outline 3 techniques that are useful in the diagnosis of Enterobiasis.

Answer 28

• Macroscopic technique. Looking for the worms in the perianal region, 2-3 hours after the infected person falls asleep.
• The transparent Scotch tape technique.
• Analysing samples obtained from under the fingernails microscopically. The infected person may have scratched the anal area and picked up some pinworm eggs which could be used for diagnosis .

Question 29

State some of the measures that are effective in preventing the spread of Enterobius vermicularis.

Answer 29

• Washing your hands with soap and warm water after using the toilet, changing diapers and before handling food.
• Infected people should shower every morning to help remove a large amount of the eggs deposited at night.
• Infected people should not co- bathe with others during their time of infection.
• Cutting fingernails regularly and avoid biting the nails , and scratching the perianal area.
• Frequent changing of underclothes and bed linens first thing in the morning - this prevents possible transmission of eggs in the environment and risk of infection. The items should not be shaken , and should be laundered with hot water.

Question 30

Why is showering a better method than taking a normal bath for individuals infected with Enterobius vermicularis?

Answer 30

Showering prevents potential contamination of the bath water with pinworm eggs.

Question 31

Briefly describe the Scotch tape technique used in diagnosis of Enterobiasis.

Answer 31

• Touch the perianal area with transparent Scotch tape to collect possible pinworm eggs around the perianal area first thing in the morning before any bowel movements.
• If the person is infected, the eggs on the tape will be visible for examination under a microscope.
• The eggs are football shaped , have a thin outer shell and have infectious larvae within the egg.
• The tape method should be conducted on 3 consecutive mornings, right after the infected person wakes up and before he / she does any washing.

Question 32

Common name for Trichuris trichiura?

Answer 32

Whipworm

Question 33

State the standard method of diagnosing and the drugs effective in the treatment of Trichuris trichiura infections.

Answer 33

• Stool exam for O&P - microscopically identifying the whipworm eggs in a stool sample. Concentration procedures may be used in light infections.
• Albendazole
• Mebendazole
• Ivermectin
• Pyrantel Pamoate - at times
• Iron supplements can also be prescribed if the person has anemia.

Question 34

What is the main site of infection of Trichuris trichiura in the human body ?

Answer 34

Cecum /colon

Question 35

Briefly describe the life cycle of Trichuris trichiura parasites.

Question 36

State some of the clinical manifestations associated with Trichuris trichiura infections.

Answer 36

• Frequent painful passage of stool that contains a mixture of mucus, water and blood.
• Lower abdominal pain.
• Abdominal distension.
• Diarrhea.
• Rectal prolapse.
• Heavy infection can lead to severe anemia, growth retardation and impaired cognitive development.

Question 37

Symptoms of severe Trichuris trichiura infections include ?

Answer 37

• Profuse bloody diarrhea.
• Cramps.
• Tenesmus.
• Urgency and rectal prolapse - from increased peristalsis that occurs in an effort to expel the worms.
• Appendicitis - if the worms migrate to the appendix.
• Intestinal hemorrhages , with mucosal cell destruction and infiltration of inflammatory cells - due to burrowing of the anterior ends of the worms into the mucosa of the intestines.