Hookworm Infection and Pathogenesis Quiz

Soil Transmitted Helminths (STH 2)

• Hookworms are Ancylostoma duodenale and Necator americanus
• These hookworms infect 576-740 million people globally
• Approximately 10% of infected individuals develop anemia
• Hookworms can persist in the host for years, impacting physical and intellectual development in children and economic development in communities.

Hookworm Distribution

• Hookworms are widespread in tropical and subtropical regions
• Prevalence can reach as high as 90% in specific communities
• Rural areas with moist, shaded soil and inadequate sanitation are associated with higher hookworm prevalence
• Agricultural laborers are at elevated risk of hookworm infection due to exposure

Demographic Prevalence

• Hookworm infection is closely linked with poverty
• Inadequate sanitation and poor housing conditions are contributing factors
• Limited access to essential medications plays a role in the prevalence
• Prevalence decreases as countries develop and conditions related to sanitation improve

Route of Infection

• Hookworm infection occurs through skin exposure to larvae present in soil contaminated with human feces.
• Adults and agricultural workers are at equal or higher risk than children

Hookworm Characteristics

• Two key species: Necator americanus and Ancylostoma duodenale
• Adult hookworms measure 10-15 mm in length
• Both species have buccal capsules (primitive mouths)
• A. duodenale has two pairs of teeth, while N. americanus possesses cutting plates. These adaptations facilitate attachment to the intestinal mucosa.
• The ova of both species share morphological similarities. Ova have a thin, clear, smooth, colorless shell with the embryo inside

Hookworm Prevalence Map

• A global map displays hookworm prevalence rates, with darker shades correlating to higher rates.

Hookworm Life Cycle

• First-stage larvae (rhabditiform) are short and non-infective
• Third-stage larvae (filariform) are longer and infective.
• Filariform larvae penetrate the skin, enter the bloodstream, and migrate to the lungs
• The larvae travel up the trachea and are swallowed
• They reach the small intestine and mature into adult hookworms.
• Adult females produce eggs, which are passed in the feces.

Pathogenesis

• Mild infection is typically asymptomatic
• Severe infection can lead to nausea, fatigue, vomiting, abdominal pain, anorexia, diarrhea, and iron-deficiency anemia.
• Skin penetration may lead to a skin lesion called cutaneous larva migrans.

Filariform Larvae

• Third-stage larvae are 500-700 µm long
• Rapid penetration of the skin (most frequently the feet) occurs after 5+ minutes of skin contact with soil containing viable larvae.
• They feed by puncturing and feeding on capillaries in the jejunum.
• A localized ground itch may accompany penetration.
• Penetration is more common with Ancylostoma compared to Necator

Signs and Symptoms - Pruritus

• Early symptoms vary with exposure intensity
• Necator causes local irritation (ground itch) at the skin invasion site
• Skin reaction might be intensely pruritic, erythematous, or vesicular, and often on the feet or hands.
• Differentiate from creeping eruptions due to cat or dog hookworms (Ancylostoma braziliense)

Loeffler's Syndrome

• Larvae burrow into lung venules and embolize into alveoli
• It is a mild, usually asymptomatic, alveolitis associated with eosinophilia.
• Hookworms are one of the causes of pulmonary infiltrates and eosinophilia (PIE) syndrome, along with nematodes like Ascaris and Strongyloides species.
• Common symptoms include fever, malaise, cough, wheezing, and dyspnea.
• Coughing helps larvae reach the mouth and are then swallowed to the intestine

Hookworm Lifespan

• Necator has a 5-year lifespan
• Ancylostoma has a 1-year lifespan
• As worms mature in the jejunum, patients can experience diarrhea, vague abdominal pain, colic, and/or nausea

Intestinal Symptoms and Anemia

• Maturing worms in the jejunum can cause diarrhea, general abdominal pain, colic, and nausea.
• Severe iron-deficiency anemia may lead to related factors like headache, palpitations, shortness of breath, and edema.
• Each Necator worm ingests 0.03 mL of blood daily, whilst each Ancylostoma worm ingests 0.2 mL per day

Anemia

• Host anemia is proportional to diet, iron reserves, and worm burden.
• Threshold worm load for producing anemia varies geographically, ranging down to 40 worms in areas with low iron intake.
• Severe anemia leads to impaired intellectual and physical development in children.
• It can also result in cardiovascular complications in adults.
• Young women, especially pregnant women and agricultural laborers are more prone to symptomatic anemia.

Diagnosis & Treatment

• Diagnosis involves finding ova or larvae in feces. Use stool culture (Harada-Mori technique) helps distinguish larval varieties (e.g. hookworm and Strongyloides)
• Treatment options include albendazole and mebendazole.
• Preventative measures include wearing shoes or gloves when working outdoors in areas with contamination.

Cutaneous Larva Migrans

• Animal hookworm larvae cause creeping eruptions (cutaneous larva migrans), characterized by serpentine skin lesions
• Cutaneous larva migrans (CLM) is a skin disorder in humans caused by various hookworm larvae.
• CLM is literally "wandering larvae in the skin"
• Common causative species include Ancylostoma braziliense, Ancylostoma ceylanicum, and Ancylostoma caninum. (dog and cat hookworms)
• The infection manifests as a pruritic red skin eruption typically seen on the feet or hands.

Strongyloides stercoralis

• It is a common enteric helminthic parasite globally that often manifests as asymptomatic or mild gastrointestinal symptoms
• In immunocompromised individuals infection can be severe, with mortality rates near 60-85%.

Strongyloides stercoralis Life Cycle

• Larvae exist in two forms: filariform (infective) and rhabditiform (free-living)
• Infection results from skin contact with contaminated soil
• The larvae penetrate the skin and migrate to the lungs
• The larvae travel up the respiratory tract and are swallowed
• They mature to adult females in the small intestine
• Adult females are parthenogenic (self-fertilizing) to produce eggs
• The eggs typically develop into rhabditiform larvae and are excreted in the feces
• Larvae may develop into filariform larvae leading to autoinfection

Skin Lesions

• Skin penetration by infective larvae can cause ground itch, characterized by a pruritic papulovesicular eruption typically on feet or any area exposed to contaminated soil.
• A characteristic lesion of Strongyloides infection is the larva currens, a serpiginous urticarial rash creeping across the skin.
• Allergic response or pruritic wheals/linear urticaria may be associated with migrating larvae.

Test your knowledge on hookworm infections with this quiz. Explore the life cycle, symptoms, and pathogenesis associated with hookworm larvae. Assess your understanding of how these parasites affect human health and the mechanisms behind their effects.