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Infections Caused by Worms (Helminthic diseases) in Humans, Practice Problems and FAQs

Infections Caused by Worms (Helminthic diseases) in Humans, Practice Problems and FAQs

Have you ever heard your elders or even the doctor say that a child must be sick because of worms in his or her tummy? In fact, even when you were a kid, you must have heard your mother being after your life to not play bare feet in the soil or to wash your hands every time you eat so as you do not get worms in the tummy. The thought of worms wriggling around inside our body is a scary thought right? But, sadly, it is a reality and not a hoax created by your mom to scare you into washing hands and staying clean.

In fact, deworming is a common practice to maintain a healthy gut, not only in humans but also in pets. If you have a pet or know people with pets, you must have seen or heard that the pets are regularly fed with medicines that help in removing worms from their body.

But what are these worms and why are they so scary? How do they enter our body and what do we do if they do? Well, to answer the first question, these worms are normally members of the animal phyla Platyhelminthes and Aschelminthes and are mostly parasitic in nature. Thus, when they enter our body they get nutrition from us and in turn harm us, causing serious damage to our body. Let us learn about some of the most common diseases caused by these helminthic worms.

Table of contents

  • Ascariasis
  • Filariasis
  • Taeniasis
  • Practice problems
  • FAQs

Ascariasis

Causative agent

It is caused by the roundworm Ascaris lumbricoides which is also known as intestinal roundworm. It belongs to phylum Aschelminthes of the animal kingdom.


                        Fig: Ascaris lumbricoides

These worms live and mature in the small intestine of humans, especially children. It takes in digested food from the intestine by sucking through its mouth. A single host may harbour around 500-5000 adult roundworms.


                     Fig: Ascaris within the human small intestine

Mode of Transmission

It usually spreads by the oral-faecal route. The worm eggs enter the intestine of humans through ingestion of water or food contaminated with the faecal matter of an infected person or if a person comes in touch with soil contaminated with human or pig faeces containing eggs of Ascaris lumbricoides.

Ascaris eggs can also be transmitted through unwashed fruits or vegetables produced in polluted soil.


                                                Fig: Modes of transmission of ascariasis

Life cycle of Ascaris

After entering the intestine of humans the Ascaris eggs mature into larvae that travel through the intestinal wall and reach the heart and lungs via blood or lymph. The larvae enter the airways, after maturing for about 10 to 14 days in the lungs. They travel up the throat and are coughed up and swallowed too. During this phase, symptoms such as cough and shortness of breath. can be seen.

After being swallowed, larvae reach the intestines again and grow into male and female worms. The female worms lay a huge number of eggs which are released long with faeces.

Symptoms

The symptoms of ascariasis include muscle and abdominal pain, abnormal weight loss, fever, anaemia, blockage of intestinal passage, internal bleeding, vomiting and presence of worms and its eggs in faeces.


                                                   Fig: Symptoms of ascariasis

Diagnosis

Ascariasis can be diagnosed by looking for the presence of eggs in a stool sample, with the help of a microscope. Infection can also be recognised if worms are coughed up or passed out with stool.

Treatment and prevention

Anthelmintic medications like albendazole and mebendazole can be used to treat ascariasis. The worms are surgically removed if the infection is severe and the worms totally obstruct the digestive passage. It may, however, be substantially avoided by observing proper public hygiene and cleanliness.

Filariasis

Causative agent

Filariasis is caused by filarial worms, Wuchereria bancrofti and Wucheria malayi that look like threads and belong to the Phylum Aschelminthes.


                                            Fig: Wuchereria bancrofti

The parasitic filarial worms dwell for many years in the lymph nodes and lymphatic arteries of the lower limbs, causing chronic inflammation.

Mode of Transmission

These worms generally spread through the bite of female mosquito vectors, that is, Culex mosquito.


                                               Fig: Culex mosquito

Life cycle of filarial worm

The adult worm is filiform and is a digenetic parasite which completes its life cycle in two hosts. The primary host is human and the intermediate host is the female Culex mosquito.

The female worm is viviparous and releases numerous microfilariae which live in deep-seated blood vessels but move, at night, to the superficial vessels near the skin to be picked up by the mosquitoes.

When the mosquito bites a healthy host, the microfilariae are deposited on the skin near the site of the bite. They penetrate the skin and move into the lymphatic channels where they develop into adults.

Symptoms

The majority of filariasis infections are asymptomatic, meaning there are no visible signs of infection. Fever, chills, and nausea are symptoms of an acute infection.


                                                  Fig: Early symptoms of filariasis

Chronic infection can create obstruction of the lymph flow, causing particular regions of the body, particularly the legs and external genitals, to enlarge dramatically causing elephantiasis. Filarial worms are parasitic worms that live in lymphatic arteries and block lymph movement particularly in the lower extremities.


                                             Fig: Symptoms for chronic filariasis

Diagnosis

Microscopic examination and identification of microfilariae in a blood smear taken from the patient can be a method of diagnosis. Identification of anti filarial IgG4 antibody in the blood using routine assays can also be used as a diagnostic method.

Treatment and prevention

Anthelmintic medications are given to kill the worms.

The disease can be prevented by destroying the breeding grounds of the mosquitoes and killing the adult mosquitoes and the eggs and larvae as well. Protection against mosquito bite can also prevent filarial infection.

Taeniasis

Causative agent

Taeniasis is caused by tapeworms Taenia solium (pork tapeworm), Taenia saginata and Taenia asiatica, belonging to the phylum Platyhelminthes. It mainly infects the intestines of human beings. Taenia solium is the tapeworm species found in pork meat. It is a bisexual parasite as the male and female reproductive structures are present in the same organism.


                                                  Fig: Taenia solium

Mode of Transmission

This disease spreads by eating undercooked infected meat such as beef (T. saginata) or pork (T. solium and T. asiatica). The life cycle of Taenia solium is digenetic, that is, it requires two hosts to complete its life cycle. The primary host is man and the secondary host: is pig.

Life cycle of Taenia

Eggs are released into the faeces of an infected host and can remain in the environment for many days, even months. Cattle and pig get infected when they feed on plants grown on soil infected with such egg infested faecal matter. The eggs hatch into larvae (oncospheres) within the intestine of the animal and invade the intestinal wall to travel to the skeletal muscles of the animal. In the muscles, the oncospheres develop into an encysted larval form known as cysticerci which can survive within the animal for years.

Consumption of animal meat, infected with cysticerci results in infection in humans. The cysticerci develop into adults within the intestines and can live there for years. The adults attach to the intestinal wall using their scolex (knob like structure with suckers). The adults produce gravid proglottids out of which the posterior most one carries the embryonated eggs. This gravid proglottid detaches from the worm, travels down to the anus and is passed out with faeces.


                                                             Fig: Life cycle of Taenia

Symptoms

Usually, tapeworm infections have no symptoms or mild symptoms which include digestive problems including abdominal pain, loss of appetite, weight loss, and stomach upset.

Diagnosis

Diagnosis of taeniasis can be done by the examination of stool samples using a microscope to identify the Taenia segments (gravid proglottids) carrying the egg. Eggs can be detected in the stool only after 2 to 3 months of the tapeworm infection establishing itself within the patient.

Treatment and prevention

Oral anthelmintic drugs can be administered to treat taeniasis. Infection can be avoided by eating well-cooked meat as high temperatures destroy the larvae in infected meat.

Practice Problems

1. Match the following

 

Column I

 

Column II

1.

Ascaris lumbricoides

A

Cysticerci

2.

Taenia solium

B

Elephantiasis

3.

Wuchereria bancrofti

C

Blockage of intestinal passage

  1. 1 - A, 2 - B, 3 - C
  2. 1 - C, 2 - A, 3 - B
  3. 1 - A, 2 - C, 3 - B
  4. 1 - C, 2 - B, 3 - A

Solution: Ascaris lumbricoides is an intestinal worm which infects the intestine and can lead to blockage of intestinal passage.

Taenia solium is also known as pork tapeworm. It also infects the intestine of humans and is transmitted by feeding on pork contaminated with larval stages of the worm. Pigs act as secondary hosts to the worm and it forms encysted larvae in the muscles of the pig which are known as cysticerci.

Wuchereria bancrofti mainly infects lymph nodes and resides in them for many years and thus, this worm goes unnoticed. It gradually causes swelling and inflammation of lymph nodes leading to a condition called elephantiasis in which the legs and genitals are massively swollen. Hence, option b is correct.

2. A female Culex mosquito bites a person and after a few months, the person notices that his external genitals and legs have enlarged and have started swelling. Name the possible organism this mosquito had transmitted to this individual.

  1. Entamoeba histolytica
  2. Taenia solium
  3. Wuchereria bancrofti
  4. Ascaris lumbricoides

Solution: The female Culex mosquito carries filarial worms such as Wuchereria bancrofti which infects lymph nodes and results in the inflammation and enlargement of legs and external genitals.

Thus, the correct option is c.

3. How does ascariasis transmit to a healthy person?

Answer: It usually spreads by the oral-faecal route when a healthy person consumes water or food contaminated with eggs Ascaris. These eggs are resistant to high temperatures and survive during cooking as well.

4. Which of these is not a method of diagnosing filariasis?

  1. Examination of stool sample
  2. Microscopic examination of blood smear
  3. Serological assay for identification of specific antibodies
  1. Only I
  2. I and II
  3. II and III
  4. I and III

Solution: Filariasis can be diagnosed by identifying the worms in the smear of the patient’s blood under a microscope. Serological assays to determine the presence of the anti filarial IgG4 antibody in the blood of the patient can also be used for diagnosis.

Examination of stool does not help in diagnosis of filaria as the worms are not passed into the stool.

Thus, the correct option is a.

FAQs

  1. Can tapeworms affect the brain?

Answer: Neurocysticercosis is caused when the encysted larvae of Taenia, known as cysticerci, are found in the brain. Symptoms include seizures and headaches are the most common symptoms. Other symptoms include confusion, lack of attention, difficulty with balance and accumulation of excess fluid around the brain. This disease can be fatal.

  1. How long does it take for the taeniasis infection to show symptoms?

Answer: Occurrence of symptoms can take months to years from the initial infection. Symptoms generally exhibit after the cysts of the tapeworm start dying.

  1. Which parts of the world have maximum occurrences of ascariasis?

Answer: Most cases of ascariasis occur in the hot and humid climate of the tropical and subtropical regions such as Asia, sub-Saharan Africa, and north and south America.

  1. Which other filarial worms are common causative agents of filariasis in Asia?

Answer: Filariasis is commonly caused by Wuchereria bancrofti all over the world. Two other worms are responsible for the occurrence of filariasis in Asia. These are Brugia malayi and Brugia timori.

Youtube Link : https://youtu.be/f2hmbRxXQ5U (1:19:39 - 1:26:18)

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Bacterial diseases in humans

Viral diseases in humans

Protozoan diseases in humans

Fungal diseases in humans

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