Helminthiases: Epidemiology, Clinical Manifestations, Diagnosis, And Treatment Of Common Parasitic Worm Infections

Introduction

Helminthiasis is an infectious disease caused by parasitic worms (helminths) that enter the human body. It is estimated that more than 1 billion people worldwide are infected with gastrointestinal helminths (1). Although the highest incidence is observed in tropical and subtropical climates, parasitic diseases are also relevant in Lithuania. More than 30,000 people in the country are infected with helminthic diseases annually, with the majority being children (2). Timely diagnosis of helminthiasis, appropriate treatment, proper preventive measures, and public education significantly reduce the incidence of these diseases. However, helminthiasis often does not present with clear clinical symptoms, making the disease difficult to identify immediately. In the diagnosis of parasitic diseases, it is important to understand the etiology, pathogenesis, and clinical manifestations of these conditions. This article reviews the most common helminthiases in Lithuania, routes of parasite transmission, clinical manifestations, general diagnostic methods, and treatment principles.

Main Features of Helminths and Diseases They Cause

Based on their morphology, helminths are divided into roundworms (ascaris, pinworms, trichinae, toxocara, and tapeworms) and flatworms (flukes and tapeworms). According to their life-cycle characteristics, they are classified as geohelminths, biohelminths, and contact helminths. Geohelminths are parasitic worms that develop in the soil. They include ascaris, whipworms, and toxocara. Biohelminths require another living organism to complete their life cycle. This group includes swine, cattle, and dog tapeworms, as well as trichinae. Contact helminths are parasitic worms whose eggs are excreted in a mature state or become mature on the human body after being released from the intestines of an infected person. The most common contact helminth is the pinworm (Enterobius vermicularis).

Helminths possess a well-developed organ system. The bodies of flatworms are flattened and covered with a plasma membrane, whereas the bodies of roundworms are cylindrical and covered with a tough cuticle. Most flatworms are hermaphrodites, while roundworms generally have separate sexes. Both groups of helminths are characterized by a high reproductive capacity; for example, a female ascaris can lay up to 250,000 eggs per day (1).

All helminths undergo a developmental cycle consisting of the egg, larval, and adult stages. Human infection occurs when eggs or larvae enter the body. The complex structure of the egg and its shell provides effective protection against various harmful environmental factors, allowing eggs to survive in the environment for prolonged periods. Helminths suppress the immune system of the host in which they parasitize, creating favorable conditions for reproduction and long-term survival in the human or animal body (for example, tapeworms can survive for up to 10 years) (1).

When parasitizing the human intestine, helminths cause various gastrointestinal symptoms and systemic reactions in the body (Table 1). The clinical manifestations of helminthiasis are highly polymorphic, and not all infections are characterized by clear clinical symptoms (e.g., diarrhea) (Table 2). The symptoms and severity of the disease depend on the species of parasite and the extent of the infestation.

Most Common Helminthiases in Lithuania

In Lithuania, parasitic diseases account for only 0.17% of all infectious diseases, with the majority being helminthiases (2). According to data from the Centre for Communicable Diseases and AIDS (ULAC), the incidence of these diseases in the country has decreased over the past decade, but rates remain high among children attending preschool and primary school institutions, particularly in rural areas. The incidence of trichinellosis in the country is gradually decreasing but remains higher than the European Union average. An increasing incidence of echinococcosis has also been observed. Understanding the pathogenesis of parasitic diseases and recognizing their clinical manifestations help ensure timely diagnosis and treatment. The incidence of helminthiases can be reduced by following basic hygiene practices and implementing appropriate preventive measures.

Enterobiasis

Enterobiasis is one of the most common helminthiases worldwide (5). The disease is caused by Enterobius vermicularis, commonly known as pinworms. These worms are 3-10 mm in length.

Enterobiasis is widespread among children attending kindergartens and other childcare or educational institutions (2). However, due to delayed diagnosis, poor personal hygiene, and a lack of knowledge about parasitic diseases, children often transmit the infection to adults as well.

The source of infection is a person suffering from enterobiasis who releases the eggs of the pathogen into the environment. A person becomes infected when pinworm eggs enter the mouth through contaminated hands or food. Once a mature pinworm egg enters the human body, a larva emerges in the small intestine. It penetrates the intestinal mucosa, grows, and matures into an adult worm. Fertilized female pinworms emerge from the rectum at night and deposit eggs in the skin folds around the anus, where they mature on the human body within 4-6 hours. Pinworm eggs may also be spread by flies. The disease can persist for a long time because an infected person contaminates the surrounding environment with pinworm eggs while scratching the anal area, contaminates their fingers, and then becomes reinfected by touching their mouth. Usually, all family members eventually become infected. Often, enterobiasis, like other intestinal parasitic infestations, does not cause specific symptoms. Infected patients may experience general weakness, fatigue, abdominal pain, nausea, and decreased appetite. Only about 30 days after infection do the worms emerge through the anus and lay eggs. At this stage, intense itching around the anus, especially at night, occurs. In cases of severe infection, secondary bacterial infection of the perianal area may develop due to irritation and scratching (6). Timely treatment easily cures the disease. Delayed diagnosis, particularly in cases of heavy parasite infestation, can lead to complications. Pinworms that accumulate in the appendix can cause appendicitis, while those that enter the urinary tract or genital organs can cause inflammation of these organs. The disease may also lead to allergic reactions manifested by various skin rashes and blood eosinophilia. Pinworms can also be a cause of urinary incontinence (7, 8, 15). Enterobiasis is diagnosed by microscopic examination of the skin folds around the anus, where pinworm eggs are detected. Pinworm eggs are sometimes found in feces, urine, or vaginal diagnostic smears. In some cases, enterobiasis is diagnosed by identifying adult worms during an anorectal or vaginal examination. Upon diagnosis of enterobiasis, treatment with anthelmintic drugs is prescribed (Table 3). The first-line drug is mebendazole. Albendazole may be used as an alternative. Children under 2 years of age are recommended to receive a single dose of albendazole 200 mg, repeated every 2 weeks thereafter (9). All individuals who have been in contact with the patient should be examined and treated. All contacts should be examined and treated. It is important to explain proper hygiene practices to patients, including washing hands after using the toilet and before eating or preparing food, keeping nails short, and avoiding nail-biting. After treatment, it is recommended to change all personal and bed linens, boil them, and wash children's toys.

Ascariasis

Ascariasis is a helminthic disease caused by roundworms, Ascaris lumbricoides. Adult ascarids are cylindrical and range from 15 to 40 cm in length (4). Ascariasis is widespread worldwide. According to the World Health Organization, one-quarter of the world's population is infected with ascariasis (9). In Lithuania, 300-500 individuals become infected and develop the disease each year, most commonly preschool and younger school-age children (4). However, official data do not reflect the true prevalence of this helminthiasis among the population. Individuals with mild forms of the disease usually do not seek medical attention. According to ULAC data, the number of individuals infected with ascarids is increasing in Lithuania: 84 cases of ascariasis were registered in 2016 and 91 in 2017 (10). The source of infection is a person suffering from ascariasis. A person becomes infected by ingesting ascarid eggs through soil-contaminated hands, by eating unwashed vegetables, fruits, or berries, or by drinking untreated water from open water sources. When mature ascarid eggs are swallowed, larvae emerge in the small intestine. The larvae penetrate the intestinal wall and are carried throughout the body via the bloodstream. They migrate to the lungs, move through the bronchioles and bronchial mucosa, ascend to the trachea and nasopharynx, are swallowed, and then re-enter the small intestine through the stomach. In the small intestine, the worms grow and reach sexual maturity within 2-2.5 months. Fertilized females lay eggs in the intestine, which are excreted into the environment (soil or water) with the feces. In the soil, the eggs mature within 1-1.5 months. Adult ascarids live in the human body for approximately 1-1.5 years before being excreted with the feces. Humans most commonly contract ascariasis during the summer and autumn, when mature helminth eggs accumulate in the soil. Ascarid eggs can contaminate food through dust and may also be spread by flies. The disease often goes unnoticed and is detected incidentally during stool examinations or when adult Ascaris lumbricoides worms are passed in the feces. During the early stage of the disease, when larvae are migrating through the body, allergic reactions and asthma attacks are common. At this stage, no Ascaris eggs are found in stool examinations. Later, when adult worms parasitize the body, patients may complain of reduced appetite, dizziness, nausea, abdominal pain, and general weakness. Children may experience drooling, teeth grinding at night, night hallucinations, bloating, and abdominal pain. The course of ascariasis may lead to complications such as intestinal obstruction, mechanical jaundice, acute pancreatitis, and appendicitis (15). During vomiting, Ascaris worms may be aspirated into the respiratory tract, causing suffocation. Ascariasis is diagnosed by detecting Ascaris eggs in the patient's stool. In some cases, adult worms can be observed when they are passed in the feces. During pulmonary larval migration, microscopic examination of sputum may reveal larvae. Treatment is necessary for all infected individuals, including those without symptoms, to prevent complications such as biliary migration, intestinal perforation, and disease transmission. The first-line treatment is mebendazole. A single dose of albendazole 400 mg may also be used. Stool examination is repeated after 2 weeks. If eggs are still detected, treatment is repeated. All individuals who have been in contact with the infected person should also receive treatment. Since Ascaris eggs are excreted in the stool of infected individuals, environmental contamination with human feces must be prevented. Gardens and orchards should not be fertilized with human feces. Hands should be washed after using the toilet, after working in gardens or orchards, and before eating or preparing food. Only washed fruits, berries, and vegetables should be consumed, and water from open water sources should not be drunk. Flies should be controlled, and food should be protected from contamination by them.

Toxocariasis

Toxocariasis is caused by the larvae of the roundworms Toxocara canis (dog roundworm) and, less commonly, Toxocara cati (cat roundworm). More than 150 cases of toxocariasis are registered annually in Lithuania. The disease most commonly affects children aged 7-14 years (2). However, the actual prevalence is higher because individuals with mild forms of the disease often do not seek medical attention or receive an incorrect diagnosis. The source of infection is infected dogs and cats. Only in their bodies do the worms mature, develop, and lay eggs. A mature female worm lays approximately 200,000 eggs daily, which are excreted into the environment (soil and water) with feces. Humans cannot become infected directly from dogs or cats. Once in the soil, the eggs mature within 2-3 weeks and only then become infectious to humans and animals. These helminth eggs are highly resistant to environmental conditions and may remain viable in the soil for up to 8 years or longer (12). Animals become infected by ingesting mature Toxocara eggs from the environment. Infected females can also transmit the infection to their offspring through the placenta and milk. Humans become infected by ingesting mature Toxocara eggs. Since these eggs mature in the soil, infection occurs through contaminated hands, consumption of unwashed fruits, berries, and vegetables, and, in children, through playing in sandboxes or green areas contaminated with dog and cat feces. In the human intestine, the eggshell dissolves and releases a larva, which penetrates the intestinal mucosa and enters the bloodstream. The blood carries the larvae to the liver, heart, lungs, kidneys, pancreas, eyes, and other organs, where they settle. Over time, they become encapsulated and eventually degenerate. In many cases, particularly when only a small number of larvae enter the body, the disease may be asymptomatic. However, patients may experience fever, although body temperature is usually only mildly elevated. Bronchitis, dry cough, shortness of breath, and frequent nocturnal coughing fits may develop. In severe cases, enlargement of the spleen, liver, and lymph nodes may occur, along with abdominal pain. Patients may also experience nausea, vomiting, and diarrhea. In some cases, skin rashes may be the only manifestation of the disease. As with other helminthiases, eosinophilia is commonly observed in the blood, although its absence does not exclude a diagnosis of toxocariasis. Migrating larvae may enter the eyes and impair vision. Toxocariasis is characterized by a prolonged course, lasting months or even years, and by frequent relapses (4). The diagnosis of toxocariasis is complex. The disease often lacks specific symptoms, and its manifestations are vague and highly polymorphic. As a result, diagnosis is frequently established several years after parasite invasion. Toxocariasis should be suspected in cases of prolonged unexplained fever, pneumonia, hepatomegaly, and reliable epidemiological evidence. The diagnosis is confirmed by serological blood tests that detect antibodies against Toxocara. Asymptomatic toxocariasis does not require treatment. Treatment is recommended in the presence of clinical symptoms and/or eosinophilia. Albendazole is the first-line drug for toxocariasis, although mebendazole may also be used. During treatment, the death of numerous larvae can trigger intense inflammatory reactions; therefore, oral glucocorticosteroids are recommended both before and during treatment as premedication (1). To evaluate treatment effectiveness, repeat blood tests are performed, monitoring specific antibody titers, decreases in peripheral blood eosinophilia, and regression of clinical symptoms (9). The most important preventive measure is regular deworming of dogs and cats. Pet owners should prevent animals from contaminating the environment with feces and should collect and properly dispose of pet waste. Unwashed fruits, berries, and vegetables should not be consumed. Children's play areas should be kept away from dogs and cats. Sandboxes should be placed in sunny locations and covered when not in use.

Trichinellosis

Trichinellosis is an acute disease of humans and animals caused by roundworms of the genus Trichinella. Approximately 11 million people worldwide are diagnosed with trichinellosis each year. People of various professions and all age groups are affected, with children under 15 years of age accounting for about 20% of all cases (4, 11). The main reservoirs of the causative agents are wild and domestic animals, carnivores, omnivores, and marine mammals. In Lithuania, the principal hosts of trichinellosis are foxes, pigs, stray dogs, mice, and deer (11). People become infected with this helminthiasis by consuming raw or undercooked meat from infected pigs or deer containing cysts with Trichinella larvae. When the meat enters the stomach, gastric and pancreatic enzymes break down the muscle fibers and larval capsules. The released larvae penetrate the mucosa of the small intestine, mature, and develop into adult worms. Fertilized females begin producing live larvae, which are carried throughout the body via the lymphatic system and bloodstream, entering skeletal muscle fibers. Within 4-5 weeks, a capsule forms around each larva. The larvae can remain viable within these capsules for several years. Trichinella pseudospiralis is the only species of Trichinella that does not form capsules in muscle tissue. The incubation period ranges from 3 to 45 days, most commonly 10-25 days. Clinical manifestations after consumption of infected meat range from asymptomatic infection to severe disease with complications. The clinical picture depends on the location of the parasite. At the onset of the disease, when the worms are located in the intestine, patients experience abdominal pain, diarrhea, vomiting, and fever. Later, as the larvae migrate into the muscles (approximately 1 week after infection), facial and periorbital edema develop, conjunctivitis occurs, body temperature rises, and muscle pain, skin rashes, insomnia, anxiety, and occasionally hallucinations may appear. Inflammation of the upper respiratory tract, dry cough, and enlargement of the liver, spleen, and peripheral lymph nodes may also occur. In severe cases, complications such as lung damage, heart failure, and central nervous system involvement leading to psychosis, paralysis, or coma may develop (13). In mild infections, symptoms may be absent. In children, trichinellosis is generally mild and may manifest as a transient fever, mild muscle pain, and slight tissue swelling. Clinical symptoms such as acute fever, muscle pain, and facial swelling help raise suspicion of the disease. The diagnosis is supported by epidemiological history, including similar illness among contacts or a group of individuals who consumed the same meat. Blood tests reveal eosinophilic leukocytosis, which correlates with disease severity. Elevated muscle enzyme activity in peripheral blood, including creatine phosphokinase and lactate dehydrogenase, is also frequently observed. Serological blood tests are performed to confirm the diagnosis. Positive serological results generally appear 10-15 days after infection, peak within 6-12 months, and then gradually decline. Paired serum samples are used to confirm the diagnosis. Differential diagnosis of trichinellosis is important because many diseases can cause similar clinical manifestations. Trichinellosis must be distinguished from influenza, salmonellosis, allergic reactions, dermatomyositis, leptospirosis, and typhoid fever. Trichinellosis is treated with anthelmintic drugs such as albendazole and mebendazole. Glucocorticosteroids are administered together with anthelmintic therapy to reduce hyperallergic reactions (1). Individuals who have experienced moderate or severe trichinellosis are monitored in a healthcare facility for 6-12 months. A high incidence of trichinellosis persists in Lithuania. To reduce the incidence of this disease and the number of outbreaks, it is important to ensure the safe consumption of meat. Meat from pigs, deer, and other wild animals must be tested in veterinary laboratories before being used for food preparation or for feeding domestic animals. Rodents are the main carriers of trichinellosis in nature; therefore, rodent control measures should be implemented on farms. Trichinella parasites remain viable even when meat is smoked, salted, or processed by similar methods. Raw and thermally processed meat should be ground separately, and meat grinders must be thoroughly cleaned before being used to process other products.

Tapeworms

Tapeworms are flatworms. Several species of tapeworms can parasitize the human body. The most important are fish, beef, pork, dog (echinococcus), and dwarf tapeworms. Over the past 10 years, almost 300 tapeworm infections have been registered in Lithuania, most of them cases of echinococcosis (14). In addition, between 2007 and 2016, the incidence of echinococcosis increased, particularly due to a significant rise in cases of alveolar echinococcosis (2, 14). Unlike many other helminth infections, echinococcosis more commonly affects older individuals. Higher incidence rates are recorded among rural residents. Tapeworms usually pass through several intermediate hosts during their life cycle before reaching the definitive host. Depending on the species, humans may serve as intermediate hosts (dog tapeworm), definitive hosts (fish, beef, and dwarf tapeworms), or both definitive and intermediate hosts (pork tapeworm). The fish tapeworm (Diphyllobothrium latum) causes diphyllobothriasis. It is the largest of all tapeworms, reaching lengths of up to 10-20 meters. It parasitizes the intestines of humans, dogs, and cats and can remain viable in the human body for up to 30 years. Infection occurs through the consumption of raw or undercooked fish containing fish tapeworm larvae. Taeniarhynchosis is caused by the beef tapeworm (Taeniarhynchus saginatus). The parasite inhabits the human small intestine and can reach a length of 5-10 m. Human infection occurs through the consumption of raw or insufficiently cooked beef containing beef tapeworm larvae... For more information, read the publication "Internistas" No. 10, 2018. Dr. Akvilė Rudėnaitė Vilnius University Hospital Santaros Clinics