Hookworms Flashcards
Hookworms are geohelminths of two main species
Ancylostoma duodenale (hooked mouth)
Necator Americans( American murderer)
Epidemiology of hookworms
Ancylostoma duodenale ( old world) was prevalent along Mediterranean coast of Europe and Africa and northern India, China and Japan
Necator Americanus ( new world hookworm) was prevalent in central and south America, Central and south Africa Southern India and southern Pacific region
Hookworm disease is prevalent throughout the tropics and subtropics affecting > 900million people
Conditions favoring hookworm infection
Presence and dispersal of eggs in soil due to improper sanitation ( open defecation)
Favorable environmental factors ( temperature 23-33° c ) sandy/ loamy soil with sufficient moisture allowing growth of worm in soil
Opportunity for larva to infect people through exposed skin surfaces coming into contact with contaminated soil
Which of the two is more pathogenic ?
Ancylostoma duodenale (ancylostomiasis)
Adult worm habitat of ancylostoma duodenale
Small intestine mainly the jejunum
T/F:Hookworm is oviparous
True
Morphology of A. Duodenale Egg
Ovoid or elliptical
Measures 60 by 40um
Colourless, not bile stained.
Is segmented
Surrounded by a thin transparent hyaline shell membrane
A single Ancylostoma duodenale lays ___ eggs daily
15000- 30000
Morphology of the adult A duodenale worm
Stout cylindrical unsegmented nematodes
Pale pink or greyish white , may appear red due to ingested blood
Body curved(dorsal concave, Ventral convex) with the anterior end constricted and bent in the same direction as the body curvature. Appears like a hook
Has buccal capsule reenforced with chitin carrying 6 teeth
Mouth directed dorsally
Adult A. Duodenale male Is smaller
The female is larger
The male A. Duodenale has an umbrella shaped copulatory bursa
The female does not
A. Duodenale male genital canal opens into cloaca with anus
Female’s vulva opens ventrally @the junction of middle and post 1/3 of the body
A. Duodenale male has two long retractile bristle like copulatory spicules and a single testis
Has vagina leading to two coiled ovarian tubes and two uteruses
T/F: the copulatory pair presents a Y shaped appearance
True : During copulation the male attaches it’s bursa to the vulva
Less pathogenic
Necator Americanus ( Necatororiasis)
Egg morphology
Slightly larger but otherwise similar to A. Duodenale
Female N. Americanus lays how many eggs
6000- 10000
Morphology of the adult worm
Slightly smaller than A. Duodenale
Anterior end bent in the opposite direction to the body curvature
Have a smaller buccal capsule with 2 pairs of cutting plates
Female vulva is in the middle of the body
Male corpulatory structures fused at the end to form a barbed tip
A duodenale male has 2 separate specules.
N. Americans male has 2 spicules fused at the tip
A. Duodenale female vulva located posteriorly
N. Americans female Vulva located anteriorly
The life cycle of nematodes:
6 stages: egg( embryo) four larval stages( rhabditiform, filariaform) the adult
Examples of helminths that require no intermidiate host
Ancylostoma duodenale
Necator Americanus
Ascaris lumbricoides.
Truchuris Truchuria
Enterobias vermicularis
Hymenolopis nana
Life cycle of hookworms
- Eggs are passed in stool
- Under favourable conditions larvae hatches from eggs in 1 to 2 days to become free living in soil. These rhabditiform larvae feed on bacteria and organic matter in soil
- After 5-10 days they become non feeding filariaform ( 3rd stage) that are infective .
- On contact with human host they penetrate the skin, and are carried through the veins to the heart and then to the lungs . They penetrate to pulmonary alveoli, ascend the bronchial tree to the pharynx and are swallowed.
- The larvae reach the jejunum where they reside and mature into adults. Penetration and attachment to intestinal walls cause blood loss.
Hookworms become sexually mature adults____ weeks post penetration
5-6 weeks
What is hypobiosis
Some filariaform larvae of A.duodenale following invasion may penetrate the musculature where they remain dormant, resuming development at a later time
Modes/ Routes of infection
- Penetration of skin- bare foot, hands in farmers and miners
- Oral transmission- contaminated water, or vegetables or fruits.
- Transmammary and transplacental transmission
Transmammary transplacental transmission
A. Duodenale may be developmentally arrested and reactivated in pregnancy and infect the infant causing Iron deficiency anaemia and potential mortality
Clinical manifestations
Symptoms caused by larvae.
Ground itch- severe local itching
A rash may develop
Creeping eruption( cutaneous larva migrans)
Respiratory manifestations- bronchitis, bronchopneumonia, and rarely loeefler syndrome
Geohelminths
Direct life cycle that requires no intermidiate host or vectors
The parasitic infection ocurs through faecal contamination of soil, foodstuffs and water supply
- Ascaris Lumbricoides
- Truchuria trichuris
- Ancylostoma duodenale
- Necator Americanus
-Strongyloides stercoralis
List intestinal and filarial worms under acquisition and geoheminths
By ingestion
By skin penetration
Acquisition by insect bite
By ingestion:
EAT
Enterobias vermicularis
Ascaris lumbricoides
Trichuris trichuria
Toxocara canis/catis
Trichinella spiralis- pork
Acquisition by skin penetration:
SAN
Strongyloides stercoralis
Ancylostoma duodenale
Necator Americanus
Acquisition by insect bite
LOW
Loa loa
Onchocercha volvulus
Wuchureria bancrofti
Describe the causes,clinical features and diagnosis of loeffler syndrome
It is a transient respiratory disorder characterized by accumulation of eosinophils in the lungs
Causes- drugs, parasitic infections that transit through the lungs during their lifecycle( ascaris lumbricoides, necator Americanus , Ancylostoma duodenale, Strongyloides stercoralis, Ancylostoma duodenale, Toxocara canis
Clinical features - cough, fever, malaise, wheezing, dyspnea
Diagnosis - mild eosinophilia, elevated IgE parasites and ova in stool, larave in sputum
Migrating opacity in chest x-ray
Treatment: treat parasitic infection
Symptoms caused by adult hookworms
Microcytic hypocromic anaemia
Dyspnea-
Palpitations
Dizziness
Severe Hookworm anaemia could lead t cardiac failure
GI symptoms
- epigastric pain
- Dyspepsia
- Vomiting and diarrhoea
- Red/ black stool
Protein deficiency
Puffy face , foot anf ankle edema
Stunted growth, delayed puberty, mental dullness in children
How does hookworm infection cause anaemia
Hookworms vigoursly suck blood for their food
Chronic haemorrhage from punctured sites in the duodenum as the hookworm saliva contains anticoagulant
Deficient absorption of B12 and and folic acid
Depression of haematopoietic system by deficient intake of proteins
Hypochromic anaemia is caused by IDA while dimorphic anaemia is caused by both iron and B12 deficiency
Diagnosis
Demonstration of characteristic oval segmented eggs-
Adult hookworms my be seen in faeces
Indirect methods-
Blood exams- microcytic hypocromic anaemia with eosinophilia
Stool exam: presence of occult blood and Charcot layden crystal
Chest x-ray may show migrating larvae
Treatment
When HB is very low anthelmintic drugs- should not be used before correcting the anaemia
Albendazole
Mebendazole
Pyrantel pamoate
Thiabendazole
Bephenium hydroxynaohthoate us active against Ancylostoma but not against necator
Prevention and control of disease
Proper sanitation - use of latrines
Proper disposal of waste
Avoid using human waste as fertilizer.
Useof footwear and gloves when in contact with the soil to prevent entry through skin
Treatment of patents and carriers
Education and sensitization
