What is Ascariasis Roundworm? How Do We Prevent the Infection Affecting a Quarter of the World

What is Ascariasis?

Ascariasis is an intestinal infection caused by parasitic roundworms known as Ascaris Lumbricoides. The Ascaris worms are tapered on both ends and are light pink or white in color. The worms are the largest worms to infect humans. Adult males are 15 – 30 cm, and adult females can grow as much as 40 cm in length [1].

Ascariasis affects humans and dogs.

How is Ascariasis Transmitted?

Ascariasis is spread through soil contaminated with human or pig feces. It can also be transmitted through unfiltered or improperly filtered water. Worm eggs can also enter our bodies through unwashed fruit or vegetables grown in contaminated soil.

We ingest the worm eggs when we touch contaminated dirt and then put our fingers or hands in our mouths – another reason why children are the most infected.

History of Ascariasis

The Ascaris lumbricoides worm has been around for centuries. The worm has a hard coating on its shell, which helps preserve it over time. An Ascaris lumbricoides worm has been found inside an Egyptian mummy dating 1600 B.C., and fossilized eggs have been discovered in South America from 2277 B.C.

In England, King Richard III is famous for many things. He most likely murdered his nephews so he could be king. He led the last battle of the Wars of the Roses, and his death during the battle marked the end of the Middle Ages in England. His story was immortalized in a play by Shakespeare. However, he may have another dubious distinction. In 2012, researchers from the University of Leicester analyzed his remains and found Ascaris lumbricoides roundworm eggs [5]. 

These parasitic worms have been infecting millions throughout history until developed countries implemented better sanitation.

How Does the Ascariasis Worm Cause Infection?

The lifecycle begins with adult Ascaris lumbricoides worms residing in human and pig intestines. Adult female worms can produce 20,000 eggs a day. The eggs are passed out through feces and mixed with soil.

Ingesting unfertilized eggs does not cause infection. However, fertile eggs are infective within a few weeks. These eggs make their way to our small intestines, where the larvae hatch. They then break through the intestinal barrier and travel to the lungs through blood or the lymphatic system.

The larvae mature over ten days in the lungs and are coughed up and re-enter our digestive tract again when we swallow. The larvae mature into adult worms in the small intestine, and the cycle of infection continues [1].

Unfortunately, asymptomatic individuals may never seek treatment. This means the worms in their intestines can continue to produce and shed thousands of eggs a day for years. The average lifespan is ten months to two years, and the worms do not multiply in the host. As a result, a high worm load in the intestine is often due to repeated exposure to contamination.

Diagnosis

Because many individuals have mild or are asymptomatic, early diagnosis is not often possible. Since the worms and eggs are shed through feces, medical professionals diagnose ascariasis through stool microscopy. Larger worms, particularly females, can be seen by the human eye. They can look like small pieces of white thread.

If no stool sample is available, a blood test can raise an alert to drive the further investigation. Individuals with ascariasis elevate eosinophil levels in the body. A high level of eosinophil, a type of white blood cell, indicates that the body is trying to fight some infection-causing pathogen [6].  

Symptoms

The incubation period for Ascariasis is 10 – 14 days. The incubation period is the time between when you are infected to when you develop symptoms. Most people have mild symptoms. But if the worm load in the intestines is heavy, there can be more severe consequences. For example, there could be vomiting as one of the main symptoms, which is common with infectious diseases and could lead to dehydration. 

Pulmonary (Lung):

Once larvae hatch in the small intestine, they penetrate the intestinal wall and travel to the lungs through blood or the lymphatic systems. There may be persistent cough, shortness of breath, and wheezing during this stage – similar to asthma or pneumonia. After 10 -14 days, the larvae move from the lungs to the throat, from where they are coughed up and re-enter the digestive system.

Intestinal:

Adult worms live in the intestines of infected people till they (the worms) die. This can take anywhere from ten months to two years. Additionally, larvae that re-enter the digestive system mature into adult worms. Because of this, intestinal symptoms may include:

• Abdominal pain
• Nausea and vomiting, and
• Diarrhea or bloody stools
• Worms or eggs in the stool

If worm load (the number of worms in the intestines) is high, even weight loss can occur. The worms can get tangled into a ball and travel from the small intestine to other locations. They may even obstruct the bowels or travel to and inflame the pancreas causing pancreatitis [1] [7].

Treatment for the Worms

Ascariasis can be cured. Anti-parasitic oral therapy works. According to WHO, the most common medications prescribed to get rid of ascaris worms are albendazole and mebendazole. Additionally, ivermectin, pyrantel pamoate, and a few others can be used. Pregnant women are prescribed pyrantel pamoate protect the fetus [4].

Disease Prevention and Control for Better Health

Better hygiene and sanitary conditions are the best ways to prevent an ascariasis infection. Drinking water must be purified either by filtering, boiling, or both. Washing your hands with soap before handling vegetables and fruit is essential. You must also wash raw vegetables and fruit thoroughly before eating.

People who work with pigs or handle raw pig manure must wash their hands thoroughly before touching their face, mouth, and other surfaces.

Mass Drug Administration (MDA)

WHO identifies the following demographics at high-risk for ascariasis:

• Preschool children
• School-age children
• Pregnant women and women of reproductive age
• Adults in high-risk occupations like miners and tea-pickers. 
• Additionally, those who work closely with pigs or raw pig manure are at risk of getting infected.

Apart from individual sanitary practices, governments in endemic regions must galvanize forces to build greater awareness, sanitation infrastructure and actively drive mass prevention measures.

Many countries with a large at-risk population have been treating the groups with proactive and preventive treatment. Anti-parasitic medication, often donated by pharmaceutical companies or global non-profit organizations, is delivered as a preventive measure. Usually, this type of preventive chemotherapy combines the treatment for more than one NTD. However, a prior ascariasis infection or treatment does not offer protection against future infections. 

The anthelmintic drugs used to treat ascariasis are effective in treating an immediate infection, but they do not offer longer-term protection. Reinfections are common. Another issue is that the parasites are developing resistance to the commonly-used anthelmintic drug, making it imperative to find a better alternative [4] [8].

Preventive Vaccines

A preventive vaccine that offers long-term protection would be helpful to battle STHs like ascariasis. However, it has been very challenging to develop one compared to anti-bacterial or anti-viral vaccines. According to Zawawi and Else (2020), this is partially because of the complex life cycles of the parasitic worms and incomplete knowledge of the immune mechanisms that offer protection against these STH infections. The worms are also complex organisms, which makes it difficult to pinpoint effective antigens for a vaccine [8].   

Control also starts with early diagnosis. Physicians can collect patient travel histories as vital signs in developed countries where ascariasis infections are less common. This way, healthcare professionals can diagnose and treat ascariasis cases early. It is also advisable to perform differential diagnoses for patients with vague abdominal pain, nausea, and diarrhea through discussions with peers or using a differential diagnosis platform like GIDEON.