Necator americanus MEDICAL PARASITOLOGY

THIS TOPIC IS FOR MEDICAL PARASITOLOGY

1. Unit 3: Helminths 3.1 Nematodes Prevalence , G eographical distribution, M ode of infection, H abitat , L ife cycle, P athogenesis , L aboratory diagnosis, P revention and control of:  Hookworm: Necator americanus and Ancylostoma duodenale

2. Necator americanus : Prevalence: The prevalence of Necator americanus , a type of hookworm, varies by location and age. It's most prevalent in rural areas of the tropics and subtropics, especially in sub-Saharan Africa and eastern Asia. Geographical distribution: Necator americanus is a hookworm that is found worldwide, but is most prevalent in tropical and subtropical regions. It is especially common in sub-Saharan Africa, the Americas, Southeast Asia, and southern China.

3. Mode of infection: Necator americanus is a parasitic worm that infects humans through the skin when larvae burrow into the skin. The larvae can also be ingested through contaminated food or water. Habitat : Necator americanus is a hookworm parasite that lives in tropical and temperate regions with warm, moist, and shaded environments. It's found in areas with soil that drains well and has particles of a moderate size.

4. life cycle: 1. Eggs are passed in the stool, and if they are deposited in a warm, moist place on loose soil, larvae hatch in 1 to 2 days. 2. The eggs release rhabditiform larvae, which grow in the feces or soil. 3. After 5 to 10 days, the larvae become infective. 4. When they come in contact with the human host, they penetrate the skin and are carried through the blood vessels to the heart and then to the lungs. They penetrate into pulmonary alveoli, ascend the bronchial tree to the pharynx, and are swallowed. 5. The larvae reach the small intestine, where they mature into adults. Adult worms live in the lumen of the small intestine. They attach to the intestinal wall, feed on blood (resulting in blood loss by the host), and produce eggs.

5. Pathogenesis : Necator americanus , the causative agent of hookworm disease, causes pathology in humans through two stages: larvae and adults.  Larvae stage Skin penetration : Larvae enter the skin through hair follicles, pores, or abrasions.  Migration : Larvae travel through the bloodstream to the lungs, where they enter the alveoli and ascend to the epiglottis.  Swallowing : Larvae are swallowed and migrate to the small intestine. 

6. Symptoms : Symptoms include a pruritic rash, cough, and shortness of breath.  Adult stage Attachment : Adult hookworms attach to the intestinal mucosa using their specialized mouthparts.  Feeding : Adult hookworms feed on the host's blood.  Symptoms : Symptoms include abdominal pain, diarrhea, bloating, nausea, and iron-deficiency anemia. 

7. Complications Iron-deficiency anemia Moderate to heavy infections can cause iron-deficiency anemia, which can lead to growth insufficiency and intellectual disability in children.  Protein loss Heavy infections can cause protein loss, which can lead to hypoproteinemia and kwashiorkor.  Malabsorption Adult hookworms secrete inhibitors of digestive enzymes, which can lead to malabsorption . 

8. laboratory diagnosis: The laboratory diagnosis of Necator americanus (New World hookworm) involves microscopic examination of a stool sample for the presence of hookworm eggs.  Procedure  Collect a stool sample Fix the sample in formalin Concentrate the sample using the formalin-ethyl acetate sedimentation technique Examine a wet mount of the sediment under a microscope Results

9. Early infection Stool studies may be normal, but in rare cases, the worm or larvae may be present  Eosinophilia A complete blood count (CBC) can show eosinophilia (higher than normal white blood cell count)  Other tests  PCR-based tests : These are the most sensitive tests Quantitative egg counts : These include the Kato-Katz test, concentration test, Beaver direct egg count, Stoll dilutional egg count, and McMaster techniques Treatment  Antiparasitic drugs such as albendazole and Iron supplementation for iron-deficient anemia. 

10. Prevention : Hygiene measures such as hand washing, drinking safe water, properly cleaning and cooking food, and wearing shoes   control : Deworming :  Deworm children periodically to prevent heavy intestinal helminth infections.  Vaccines : Develop vaccines to prevent hookworm infections.  Water, sanitation, and hygiene (WASH) programs : Implement programs to improve water, sanitation, and hygiene

11. Ancylostoma duodenale : Prevalence: Asia : The majority of Ancylostoma duodenale infections occur in Asia.  Africa :  Ancylostoma duodenale infections occur in Africa.  Americas :  Ancylostoma duodenale infections occur in the Americas, including isolated areas of the United States and the Caribbean.  Europe :  Ancylostoma duodenale infections occur in southern Europe and North Africa. 

12. Geographical distribution: Africa : Found in North Africa Asia : Found in India, China, Japan, and Southeast Asia Australia : Found in Australia Americas : Found in the Caribbean, South America, and isolated areas of the United States Europe : Found in Southern Europe Middle East : Found in the Middle East

13. Mode of infection: Ancylostoma duodenale , a type of hookworm, infects humans through contaminated soil or by consuming larvae How it spreads Soil Hookworm larvae pass through the feces of infected people or animals into the soil. Walking barefoot on contaminated soil can cause the larvae to penetrate the skin.  Animals Hookworm larvae can also be transmitted by contact with domesticated animals, such as dogs and cats. 

14. Fomites Hookworm larvae can also be transmitted through fomites , such as clothing that has been dried on the ground.  How it infects the body Once inside the body, the larvae travel through the bloodstream to the lungs.  The larvae are coughed up and swallowed.  The larvae travel to the small intestine, where they attach to the walls and mature.  Fertilized eggs are passed in the feces, which can infect another host.  Symptoms  Itchy rash at the site of larval penetration Fever, coughing, and wheezing Abdominal pain, loss of appetite, and diarrhea Iron deficiency anemia

15. Habitat : The habitat of Ancylostoma duodenale is the small intestine of humans and other mammals, particularly in the jejunum.  Ancylostoma duodenale is a parasitic nematode worm, also known as the Old World hookworm.

16. Life cycle: Life cycle of ancylostoma is completed in a single host. Definitive host: Humans are the only natural host. No intermediate host is required like other helminths . Infective form: Third stage _ filariform larva. No intermediate host is required and like other helminths , multiplication of worms does not occur inside the human body. Man is the only definitive host for A. duodenale . The following are the various stages of the life cycle.

17. Stage 1. Passage of Eggs from the infected Host. The eggs containing segmented ova with 4 blastomeres , are passed out in the faeces of the human host. Stage 2. Development in soil. From each egg a rhabditiform larva (250 μm in length) hatches out in the soil in about 48 hours. The rhabditiform larva moults twice, on the third day and the fifth day. It then develops into a filariform larva (500 to 600 μm in length), The infective stage of the parasite . The time taken for development from eggs to filariform larvae is on an average 8 to 10 days. Stage 3. Entrance into a New Host. The filariform larvae are infective to man . The larvae cast off their sheaths and gain entrance to the body by penetrating the skin.

18. Stage 4. Migration. . On reaching the subcutaneous tissues the larvae enter into the lymphatic or small venules . They pass through the lymphvascular system into the venous circulation and are carried via the right heartvinto the pulmonary capillaries, where they break through the capillary walls and enter into the alveolar spaces. They then migrate on to the bronchi, trachea and larynx, crawl over the epiglottis to the back of the pharynx and are unlimited swallowed. During migration or on entering the eosophagus . A third moulting takes place and a terminal buccal capsules is formed. The period taken for such migration is about 10days.

19. Stage 5. Localisation and laying of eggs. The growing larvae settle down in the small intestine, undergo a fourth moulting and develop into adolescent worms . At this stage the provisional toothless buccal capsule, formed previously is cast off and the definitive buccal capsule complete with teeth . Is formed. In 3 to 4 weeks time they are sexually mature and the fertilised females begin to lay eggs in the faeces . The cycle is thus repeated. The interval between the time of skin infection and the first appearance of eggs in the faeces , is about 6 weeks.

20. Morphology: Adult Worm: They are relatively stout cylindroid worms.  They are pale pink or grayish white, but may appear reddish brown due to ingested blood.  The body is curved with the dorsal aspect concave and the ventral aspect convex The anterior end is somewhat constricted and bent dorsally in the same direction of general body curvature. This cervical curvature gave it the name hookworm.  The mouth is not at the tip but directed dorsally. The prominent buccal capsule, reinforced with a hard chitin-like substance carries 6 teeth; 4 hook-like teeth ventrally, and 2 knob-like with a median cleft dorsally.

21. Female Worm: The female worm is larger, 10 to 13 mm long and 0.6 mm thick. Its hind end is conoid , with a subterminal anus situated ventrally.  The vulva opens ventrally at the junction of the middle and posterior thirds of the body.  The vagina leads to two intricately coiled ovarian tubes which occupy the hind and middle parts of the worm.  During copulation the male attaches its copulatory bursa to the vulva. The copulating pair therefore presents a Y-shaped appearance.  Sexes are easily differentiated by their size, the shape of the posterior end and the position of the genital opening.

22. Male Worm: The male worm is smaller than female worm 8-11 mm in length and 0.4 mm thick.  The posterior end of the male is expanded into a copulatory bursa which consists of 3 lobes; 1 dorsal and 2 laterals. Each lobe is supported by 13 fleshy chitinous rays, 5 each in lateral lobes and 3 in dorsal lobe: one dorsal and two extradorsal rays. The pattern of the rays helps in distinguishing between different species.  There are 2 long retractile bristle-like copulatory spicules , the tips of which project from the bursa .

23. Egg: The egg of hookworm is:  Oval or elliptical, measuring 60 μm by 40 μm .  Colorless, not bile stained.  Surrounded by a thin transparent hyaline shell membrane.  Floats in saturated salt solution.  When released by the worm in the intestine, the egg contains an unsegmented ovum.  During its passage down the intestine, the ovum develops. When passed in feces, the egg contains a segmented ovum, usually with 4 or 8 blastomeres . There is a clear space between the segmented ovum and the egg shell.

24. Pathogenesis : Ancylostoma duodenale is a hookworm that causes intestinal hookworm disease in humans. It's pathogenic because it causes chronic blood loss, which can lead to anemia.  Skin penetration Larvae enter the skin through thermal gradients, causing a pruritic rash called "ground itch"  Migration Larvae enter the bloodstream and migrate to the lungs, where they may cause a mild cough  Intestinal infection Larvae migrate to the small intestine, where they attach to the intestinal mucosa and mature into adult hookworms 

25. Blood loss Adult hookworms feed on blood, causing chronic blood loss and malabsorption   Symptoms  Abdominal pain Diarrhea Blood in the stool Anemia Loss of appetite Geophagy (eating soil)

26. laboratory diagnosis: DIRECT METHODS : Microscopy : • Wet-mount • Faecal egg count – Adult female hookworms produce 2,500-5,000 eggs/day • >2000 eggs/ml in women and > 5,ooo eggs/ml in males ----> Anaemia • Aspiration of duodenal contents by Ryle's tube • Adult worms in stool

27. INDIRECT METHODS : Peripheral blood smear – Microcytic , hypochromic anaemia and Eosinophilia • Stool examination – Occult blood, CharcotLeyden crystals Study of duodenal contents: Duodenal contents obtained by intubation may reveal the presence of eggs or adult Ancylostoma duodenale . X-ray: Chest X- ray is done to check lung infection by hookworm. ii) Clinical diagnosis: The patients can generally be diagnosed through following clinical symptoms.

28. Prevention : Practice good hygiene : Wash your hands with soap and water after using the toilet and before eating.  Wear shoes : Wear shoes when walking on soil that may be contaminated with human feces.  Avoid skin-to-soil contact : Don't sit on the ground without a barrier between your skin and the soil.  Dispose of waste properly : Don't use human feces as fertilizer.  Treat pets : Treat your dog or cat for hookworm. 

29. Improve sanitation : Clean up animal waste in public areas and improve sanitary disposal of human waste.  Educate : Educate people about hookworm and how to prevent it.  Take preventive medication : In areas where hookworm is common, preventive chemotherapy with benzimidazole drugs like albendazole and mebendazole can help prevent infection.  Wash fruits and vegetables : Wash, peel, and cook raw fruits and vegetables.  Avoid contaminated food and water : Don't eat foods that have soil on them or drink water that may be contaminated.

30. Control : Ancylostoma duodenale , also known as hookworm, is a parasitic infection that can be controlled with medication, improved sanitation, and education.  Medication A doctor may prescribe albendazole , mebendazole , or pyrantel pamoate to treat the infection.  The recommended dosage depends on the drug, but may be a single dose or a 3-day course.  Pregnant women may be able to take deworming medication during the second or third trimester. 

31. People with severe anemia may need iron supplements.  Sanitation Improve sanitation by disposing of human waste properly, Treat infected people, Wear shoes in areas where hookworm is common, and Improve water supplies.  Education  Educate people about good living habits. Teach people how to protect themselves from infective larvae.