Helminthic Diseases in Humans

What Are Helminths?

Helminths are large, multicellular, and morphologically similar organisms visible to the naked eye. They consist of organisms from the taxa Nemathelminthes (nematodes and roundworms) and Platyhelminthes (flatworms).

• Roundworms (Nematodes): They are bisexual and cylindrical and inhabit the intra and extraintestinal sites of the human body.

• Tapeworms (Cestodes): They are elongated, segmented, and inhabit the intestinal lumen. The larval forms inhabit the extraintestinal tissues.

• Flukes (Trematodes): They are leaf-shaped, and their prominent oral and ventral suckers help maintain their position in their original place.

What Are the Various Helminth Infections?

Ascaris Lumbricoides Infection: It is also called ascariasis. It affects approximately one million people worldwide and causes around 60,000 deaths per year, predominantly in children. They are transmitted through soil, and it is one of the most common intestinal worms. Risk factors for acquiring this infection are poor hygiene, sanitation, and the consumption of unwashed foods contaminated with human feces. Symptoms include:

• Worm in vomit or stool.

• Abdominal discomfort or pain.

• Fever.

• Vomiting.

• Weight loss.

• Abdominal swelling.

• Restlessness.

• Trouble sleeping.

Hookworm Infection: Hookworm infections affect around 740 million people. They are transmitted through the soil and widely distributed in rural areas. Wet soil supports the larva maturation from eggs. Hookworm infection is one of the leading causes of anemia in developing countries. Hookworm infection can cause the following symptoms:

• Dermatitis (a skin irritation at the penetration site).

• Diarrhea.

• Abdominal pain.

• Weight loss.

• Loss of appetite.

• Tiredness.

• Breathing difficulty.

• Irregular heartbeat.

• Cardiomegaly.

• Mental retardation in extreme cases.

• Anemia, especially in pregnant women and children.

Pinworm Infection: The Enterobius vermicularis is a small white round pinworm. The adult worm inhabits the cecum and colon and migrates to the anus after the deposition of eggs on the perianal skin. Only humans get this infection through the oral route or autoinfection (scratching the perianal areas and accidentally transferring it to the mouth). The incubation period of this worm is one to two months or longer. Eggs can survive indoors for about two to three weeks. Humans can transmit the infection to other humans by touching contaminated objects like linens, curtains, and clothing. Symptoms of this infection include:

• Irritation of intestinal mucosa.

• Anal pruritus (itching).

• Restlessness.

• Nervousness and irritability.

• Vaginitis in young adolescents.

• One-third of the infected persons are asymptomatic.

Lymphatic Filariasis: It is commonly called elephantiasis and can result in an altered lymphatic system with abnormal enlargement of body parts, causing pain and severe disability. It is spread to humans via an infected mosquito through a bite wound. The infection is acquired in childhood and causes hidden damage to the lymphatic system. Symptoms include:

• Elephantiasis (thickening of tissue or skin of the limbs).

• Lymphedema (tissue swelling).

• Hydrocele (scrotal swelling).

• Impairing the lymphatic system and the kidneys.

Echinococcosis: It is a hydatid disease caused by echinococcus organisms. Hydatid worms are also called dog tapeworms. They inhabit the small intestine; the definitive hosts are dogs and wild carnivores. The symptoms include:

• Hydatid cysts in the liver, lungs, spleen, heart, bone, brain, and eyes.

• These cysts grow several years before reaching maturity.

• Cysts may rupture and cause anaphylaxis and even death.

• There can be discomfort, nausea, and vomiting.

Strongyloidiasis: It is also known as Larva currens. This infection commonly occurs in tropical and subtropical regions. They are transmitted through direct contact with the larvae, usually through soil contamination. They migrate through the skin into the intestine and mature into adults. Most patients are asymptomatic, and immunosuppression is the risk factor for acquiring this infection. Hyperinfection can occur and increase the mortality rate in immunosuppressed individuals.

What Are the Effects on Nutrition by Helminthic Infections?

The nutritional condition of individuals infected with soil-transmitted helminths is compromised in many ways.

• Iron and protein are lost when the worms eat host tissues, including blood.

• Additionally, prolonged gastrointestinal bleeding caused by hookworms can lead to anemia, particularly in adolescent girls.

• The worms cause an increase in nutritional malabsorption.

• Certain helminths spread through the soil can also make people lose their appetite, lowering their intake of nutrients and physical activity.

Morbidity (being ill) is proportionate to the total number of worms present. Most of the time, people with mild infections are not ill. Severe infection would cause symptoms like diarrhea, stomach discomfort, nutritional deficiency, general fatigue, and poor growth. Extremely severe infections can result in gastrointestinal blockage, which needs to be surgically repaired.

What Are the Routes of Transmission?

• Fecal-Oral Transmission: The transmission occurs when the eggs or larvae of the organism are shed through an infected person's feces and accidentally ingested through food or water by another individual.

• Transdermal Transmission: The infective larvae can penetrate actively into the skin and migrate into the gut through the tissues. Larval hookworms infect the gut and feed on blood.

• Vector-Borne Transmission: Larvae of the organism are picked up by blood-sucking arthropods like mosquitoes, ticks, and houseflies and increase in number. When they bite or sit on human beings, the infection is transmitted.

• Predator-Prey Transmission: When the predator eats infected prey animals, it can acquire helminthic infections, and the eggs are produced and developed in its body.

How Are Helminthic Infections Diagnosed?

A definitive diagnosis can be obtained by studying the feces sample under a microscope. A quantitative egg count analysis will help arrive at insight into the infection intensity. DNA-based tools have been used recently to identify the infection. PCR (Polymerase Chain Reaction) assays will help accurately diagnose the type of worm. Rapid serological testing is used in identifying filariasis.

Capsule Endoscopy: Capsule capsule-containing camera helps find the worm attached to the gut surface.

How Are Helminthic Infections Managed?

Mass Drug Administration (MDA) helps manage and works as a preventive treatment in a community. MDA is given for infectious diseases like river blindness, lymphatic filariasis, hookworm infection, Ascaris infection, whipworm infection, and schistosomiasis. Since these drugs are inexpensive, it is easy to follow the MDA protocol. MDA is conducted annually, and door-to-door drug distribution is carried out. The WHO model of essential medicines for helminthics is listed below:

Anthelmintics

• Intestinal Anthelmintics: Albendazole, Levamisole, and Niclosamide.

• Antifilarials: Albendazole, Ivermectin, and Diethylcarbamazine.

• Antischistosomal and Anti-Trematodes: Praziquantel, Oxamniquine, and Triclabendazole.

Treating vulnerable people in endemic areas regularly is an effective method for controlling illness in helminth infections. The individuals at risk include preschoolers, students, women who are nursing or in their second or third trimester of pregnancy, and individuals who work in certain vulnerable jobs. To reduce disease occurrence, deworming, and preventive medicines are provided to people at risk of helminthic infection, irrespective of the diagnosis. Additionally, hygiene and proper sanitation awareness programs should be incorporated to reduce the disease burden.

How Are Helminthic Infections Prevented?

• Availability of clean and safe water for personal hygiene and drinking.

• Education and awareness on using latrines.

• Education and awareness about washing food.

• Sanitation and handwashing training in children.

• Educating the public to avoid uncomposted human feces as fertilizer.

• Mass drug administration.

• Restriction from barefoot walking to prevent hookworm infection.

Conclusion:

Most of the helminthic infections mentioned in this article are due to poor sanitation and hygiene. However, the ultimate cause is poverty and lack of awareness in rural areas. Disease prevention and awareness protocols should be followed in rural and suburban areas. Mass drug administration should be carried out in villages and educational institutions in areas with less access to healthcare services.