Soil Transmitted Helminths 2 (STH 2) PDF

SOIL TRANSMITTED HELMINTHS 2 (STH 2)  Hookworm Ancylostoma duodenale Necator americanus  Introduction Hookworms (Ancylostoma duodenale and Necator americanus) infect 576-740 million people and that they cause anemia in approximately 10% of those infec...

SOIL TRANSMITTED HELMINTHS 2 (STH 2)  Hookworm Ancylostoma duodenale Necator americanus  Introduction Hookworms (Ancylostoma duodenale and Necator americanus) infect 576-740 million people and that they cause anemia in approximately 10% of those infected. Hookworms may persist for many years in the host and impair the physical and intellectual development of children and the economic development of communities.  Hookworm distribution widely distributed throughout tropical and subtropical areas, with prevalence in some communities as high as 90%. the disease flourishes in rural communities with moist shaded soil and inadequate latrines. agricultural laborers have traditionally been at high risk of hookworm infection. Improper disposal of human feces and the common habit of walking barefoot are important epidemiologic features.  Demographic Prevalence Infection is closely associated with poverty inadequate sanitation, poor housing construction lack of access to essential medications are major factors in this relationship As countries develop, these factors improve, and hookworm infestation decreases  Route of Infection Hookworm infection is acquired through skin exposure to larvae in soil contaminated by human feces. (skin penetration) Adults, especially agricultural workers, are at equal or higher risk of exposure than children.  Hookworms Two important species : - Necator americanus - Ancylostoma duodenale Adults measure 10-15mm Have buccal capsules (primitive mouths)  A. duodenale has 2 pairs of teeth but N. americanus has cutting plates instead of teeth, responsible for firm attachment of adult worms to the intestinal mucosa The ova of the 2 worms are morphologically similar Thin, clear, smooth, colourless shell enclosing the embryo  After passage in feces, the first stage larva hatches in soil 1st stage larva (rhabditiform larva) is short and non infective but the 3rd stage larva (filariform) is longer and infective. The filariform larva will penetrate the skin to initiate infection Filariform larvae of hookworms are not capable of living independently and must find a host to complete their life cycle Filariform larva of Hw Filariform larva of Strongyloides stercoralis  Life cycle Penetration of the skin (hands or feet) by filariform larva from the contaminated soil Larvae enter circulation, migrate to the lungs, trachea, pharynx and are swallowed Maturation to adult stage occurs in small intestine, they attach themselves to the intestinal mucosa and suck blood Eggs are produced in the intestine and are passed in the feces  Hookworm larva Rhabditiform larva (shorter, Stouter) Filariform larva (longer, slender, infective stage)  Pathogenesis Mild infection usually asymptomatic May cause skin lesion due to migratory larva (cutaneous larva migrans) Heavy infection – nausea, fatigue, vomitting, abd pain, anorexia, diarrhea, iron def anemia  Filariform Larvae Third-stage larvae are 500-700 µm long and are capable of rapid penetration into normal skin, most commonly of the feet. Transmission occurs after 5 or more minutes of skin contact with soil that contains viable larvae. They puncture and feed on mucosal capillaries in the jejunum. Ground itch at the site of penetration is more common with Ancylostoma species than with Necator.  Signs and symptoms - Pruritus Early symptoms of hookworm infection are proportional to the intensity of exposure. Necator produces a local irritation, termed ground itch, at the site of skin invasion. An intensely pruritic, erythematous, or vesicular rash usually appears on the feet or hands. This should be distinguished from a creeping eruption due to skin migration of the cat or dog hookworm Ancylostoma braziliense.  Loeffler’s Syndrome The larvae burrow into venules and embolize the lungs, where they break into alveoli. A mild and usually asymptomatic alveolitis with eosinophilia ensues. (Hookworm is one of the causes of the pulmonary infiltrates and eosinophilia [PIE] syndrome, along with Ascaris and Strongyloides species.) Fever, malaise, cough, wheezing, dyspnea are common symptoms. Coughing brings the larvae to the mouth, where swallowing transports them to the intestine.  Approximately 5-10 weeks after skin penetration, adult females begin to produce eggs. Necator has a 5-year lifespan; Ancylostoma has a 1-year lifespan. As worms mature in the jejunum, patients may experience diarrhea, vague abdominal pain, colic, and/or nausea.  Intestinal symptoms and Anemia As worms mature in the jejunum, patients may experience diarrhea, vague abdominal pain, colic, and/or nausea. Patients with severe iron-deficiency anaemia may present with headache, palpitations, dyspnea, and edema. Each Necator worm ingests 0.03 mL of blood per day; each Ancylostoma worm ingests 0.2 mL of blood per day.  Anemia Subsequent host anemia is proportional to diet, iron reserves, and worm burden. Threshold worm loads for anemia differ nationally, with as few as 40 worms producing anemia in countries with low iron consumption. Severe anemia affects intellectual and physical development in children and the cardiovascular performance in adults Young women, especially those who are pregnant, and laborers are most susceptible to symptomatic anemia  Diagnosis & Tx Identification of ova/larvae in feces Stool culture – Harada Mori technique – Identify larval species eg. HW/ Strongyloides Treatment with Albendazole, Mebendazole Prevention as ascariasis, wear shoes or gloves when working outside in the field  Cutaneous Larva Migrans Some animal hookworm larvae can cause serpentine skin lesion known as cutaneous larva migrans or creeping eruptions Cutaneous larva migrans (CLM) is a skin disease in humans, caused by the larvae of various nematode parasites of the hookworm family. CLM literally means "wandering larvae in the skin".  Aka creeping eruption due to the way it looks; "ground itch" ; "sandworms", as the larvae like to live in sandy soil; Another name is plumber's itch. The common species causing this disease are Ancylostoma braziliense, Ancylostoma ceylanicum & Ancylostoma caninum which are parasites of dogs and cats  Since human is not the natural host, they are only able to penetrate the outer layers of the skin and thus create the typical wormlike burrows visible underneath the skin. The parasites apparently lack the collagenase enzymes required to penetrate through the basement membrane deeper into the skin.  Presentation & Tx The infection causes a red, intense itching eruption. The itching can become very painful and if scratched may allow a secondary bacterial infection to develop. The itching will stop after the parasites are dead. Treatment with Albendazole or Ivermectin orally, Thiabendazole (orally or topically) Topical freezing agents eg. ethyl chloride or liquid nitrogen may be used.  Strongyloides stercoralis Known as thread worms, reside in the intestine (disease – strongyloidiasis) Adult female is parthenogenic (self fertilizing) releasing eggs which quickly hatch into the rhabditiform larvae in intestine Rhabditiform larvae are usually passed in feces not the eggs. The larvae have short buccal cavity and a prominent genital primodium  Strongyloides stercoralis is a common enteric helminthic parasite of worldwide significance. Typically, the infection is asymptomatic or manifests as mild gastrointestinal symptoms. However, in immunocompromised persons, the infection can be devastating and carries a 60-85% mortality rate.  S. stercoralis life cycle Strongyloides larvae exist in 2 forms: filariform infective larvae and a free-living rhabditiform larvae that lives in soil independent of a human host. Infection occurs when exposed skin contacts contaminated soil. The larvae penetrate the skin and migrate via the lymphatics and venules toward the pulmonary circulation.  After penetration into the alveoli, the larvae continue their migration up the respiratory tract until they are swallowed. Filariform larvae rest in the small intestine, mature into adult females, and undergo parthenogenic reproduction  Each adult female may live up to 5 years and continue the reproductive cycle. Eggs typically mature into rhabditiform larvae within the intestine. Strongyloides is the only helminth to secrete larvae (and not eggs) in feces. Typically, larvae appear in feces approximately 1 month after skin penetration. The excreted rhabditiform larvae may again live freely in soil or be transformed into filariform larvae awaiting another human host.  Under certain conditions (eg, constipation, decreased bowel motility, diverticular disease), the larvae do not exit the host in feces and instead molt into the infective filariform larva within the intestinal lumen. These larvae are then capable of penetrating the bowel wall and traveling throughout the body. The CNS, liver, and lungs are the most common destinations of the autoinfectious larvae. This autoinfectious cycle can be accelerated in immunocompromised hosts and results in a frequently fatal condition known as hyperinfection  Epidemiology Strongyloides is endemic in tropical and subtropical areas with sporadic occurrence in temperate areas. Sub-Saharan Africa, South and Southeast Asia, Central America, and South America, and parts of Eastern Europe are considered endemic areas of Strongyloides infection. Worldwide prevalence is estimated as 2-20% in endemic areas.  Strongyloides infection is represented in all ages. However, infection may most frequently initially occur in childhood, as children are most likely to play outdoors in contaminated soil with bare feet.  Infection can range from asymptomatic to multiorgan failure. The mortality rate for patients requiring hospitalization with Strongyloides infection is 16.7%. In disseminated strongyloidiasis, the mortality rate can be as high as 70-90%.  Skin lesion Skin penetration by infective larvae can elicit ground itch, a cutaneous eruption of pruritic papulovesicular lesions. Typically, skin penetration is on the feet but may be at any site that contacted infected soil. Larva currens (racing larvae), the pathognomonic rash of Strongyloides infection, is a serpiginous urticarial rash that creeps 5-15 cm/h up the body. This rash, likely an allergic response to the migrating larvae, often manifests as a pruritic wheal or linear urticaria. This dermatologic manifestation may last hours to days but in autoinfection cycles can recur over weeks, months, and years.  The 3rd stage filariform larva (infective stage) develops in the soil It is longer and has notched rather than pointed tail Infection is by penetration of the skin by the filariform larva It undergoes “lung migration” as ascariasis and hookworm and mature to adult worm in the small intestine  In the indirect cycle, the rhabditiform larvae develop into free-living adult male & female worms which may produce eggs and non infective larvae that develop into infective larvae in the soil. The rhabditiform larvae can also develop into filariform larvae in the intestine which may penetrate the intestinal mucosa, or the perianal skin to result in autoinfection  Pathogenesis Penetration of the skin by larvae may cause allergic reaction or cutaneous larva migran usually referred to as larva currens Diarrhea, abd pain, vomitting, weight loss, pulmonary symptoms during lung migration – cough & shortness of breath Autoinfection may lead to hyperinfection syndrome. Disseminated infection occurs esp in immunocompromised pts eg. AIDS Larvae may be found in many organs, lungs, liver & heart  Diagnosis & Treatment Identification of rhabditiform and filariform larvae in human feces Usually stool culture “Harada Mori” or “Sand culture technique” is employed Treatment with Thiabendazole and prevention as with hookworm infection