Helminthiasis

Helminths are multicellular parasitic organisms that can cause a range of infections [1]. They are encountered in the areas of the developed world with poor sanitation and socioeconomic conditions, and where various vectors that facilitate their transmission are present [1] [2] [3]. More than 2 billion people are affected worldwide. Helminthiasis, is an infection caused by several parasites which are classified as [1] [2] [3] [4] [5] [6] [7]:

• Intestinal roundworms - Ascaris lumbricoides (large intestinal roundworm), Ancylostoma duodenale and Necator americanus (hookworms), Strongyloides stercoralis (threadworm), Enterobius vermicularis (pinworm) and Trichuris trichura (whipworm) are perhaps the most prevalent helminthic organisms in the world, affecting almost 1 billion people in poorly developed parts of Latin America, Africa, and Asia (China and India) [1] [3] [4] [6]. Intestinal roundworms are all introduced into the human body after ingesting food or other products from soil contaminated with parasitic eggs, thus the term "soil-transmitted helminths" is frequently used [5] [6]. Some intestinal roundworms, however, can cause an infection by invading the human host through breaks in the skin when being in contact with contaminated soil, such as Necator americanus and Strongyloides stercoralis [1] [8]. The majority of patients are asymptomatic, but a range of clinical manifestations may be seen in severe infestation, particularly in immunocompromised children and adults [4] [6] [7]. Gastrointestinal complaints (nausea, vomiting, chronic abdominal pain, diarrhea, malnutrition, reduced appetite), pulmonary symptoms (cough, dyspnea), skin rashes and perianal pruritus are some of the most common symptoms, whereas dissemination of the parasite from the intestines into other organs might occur as well [1] [2] [3].
• Tissue roundworms - Filarial parasites (Loa loa, Wucheria bancrofti, Onchocerca volvulus, Brugia malayi), Trichinella spiralis (the causative agent of trichinellosis), Dracunculus medinensis (Guinea worm), Toxocara canis and T. cati (the causative agent of visceral larva migrans), and Ancylostoma braziliense (responsible for cutaneous larva migrans) are classified into this group of nematodes as they cause infections related to other tissues in the body [2] [3] [4]. Except for trichinellosis, widely known for its acquisition through contaminated meat products, and Dracunculiasis (ingestion of water contaminated with copepods that harbor parasitic eggs) various vectors are integral parts of tissue roundworm life cycle (Anopheles, Aedes, and Culex mosquitoes, as well as black flies) [1] [2] [3]. The sub-Saharan Africa is the principal area where tissue roundworm infections are diagnosed, while Latin America and Asia are also important sites [4]. When the infection is symptomatic, clinical features include lymphedema and elephantiasis (W. bancrofti and B. malayi), conjunctivitis, chorioretinitis and visual deficits (Loa loa and O. volvulus), whereas watery diarrhea, vomiting, abdominal pain, myalgia and weakness appearing peaking in intensity approx. 2-4 weeks after ingestion of contaminated meat are the hallmarks of T. spirallis, which may be life-threatening if complications (myocarditis, encephalitis) develop [6] [7] [8].
• Flukes - The most important helminth belonging in this group are Schistosoma spp. that cause human infection after their acquisition from water sources (through swimming, fishing or drinking) being contaminated by their eggs from snails, pivotal hosts for their life cycle [3]. The clinical course involves three distinct syndromes - the swimmer's itch (manifesting as a maculopapular rash 2-3 days after infection), acute schistosomiasis (also known as Katayama fever, distinguished by fever, hepatosplenomegaly and generalized lymphadenopathy), and chronic infection, in which gastrointestinal (diarrhea, vomiting, abdominal pain, nausea) and urinary (hematuria, obstruction, dysuria, etc.) symptoms are seen, depending on the species responsible for the infection [1] [2] [3]. Other notable flukes are those infecting the intestines (Fasciola hepatica, Fasciolopsis buski) and the liver (Clonorchis sinensis and Opisthorchis viverinni).

As the majority of helminths can be diagnosed through appropriate microbiological methods, it is the physician's clinical suspicion during the assessment of the patient which plays an important role in the workup. Because helminthiasis encompasses a large number of parasitic organisms, however, a comprehensive clinical and laboratory workup is vital in narrowing the list of potential pathogens responsible for the infection. As most helminths are endemic for tropical parts of the world, a detailed patient history of recent travel to these areas, or if they resided in these parts of the world for a prolonged period of time [1] [3] [5] should be obtained. If patients did visit endemic regions, the physician should further assess if they consumed local products or were exposed to water sources that may have been contaminated [1] [3]. After performing a meticulous physical examination, laboratory workup should start with a complete blood count (CBC), which will reveal eosinophilia, one of the most important findings that point toward helminthiasis as the underlying cause of symptoms [7]. Current diagnostic strategies advise testing of feces, sputum, blood, urine, skin, and biopsies of the liver or muscle in rare cases, but the examination of feces is perhaps the main diagnostic method in the field of parasitology [1] [2] [3] [7] [8]. The majority of parasites are excreted in stool in their egg form, including all intestinal roundworms, the majority of flukes, and tapeworms as well (Taenia saginata, T. solium, Diphyllobothrium latum and Hymenolepsis nana) [1] [2] [3] [7]. On the other hand, detection of specific antibodies is available for several helminths, such as Strongyloides stercoralis, T. spiralis, lymphatic filariae (W. bancrofti and b. malayi), virtually all flukes, and T. canis and T. cati [1] [3].

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