[DISCUSSION] MODULE 3 UNIT 3 Flashcards
The phylum Nematoda is divided into classes based on the presence or absence of “(?)’, which are caudal chemoreceptors.
phasmids
The two (2) classes were earlier called Aphasmidia and Phasmidia, but now have been renamed as (?), respectively.
Adenophorea and Secernentea
This module unit will deal with the phasmid nematodes belonging to the class Secernentea.
Medically important phasmids include (?)
Ascaris lumbricoides, Enterobius vermicularis, hookworm species, and Strongyloides stercoralis.
The specific name of Ascaris lumbricoides has been derived from its resemblance with earthworm ([?], meaning earthworm in Latin).
lumbricus
Two species of hookworms are human parasites:
(1)Ancylostoma duodenale
2) Necator americanus
(Greek ankylos-hooked, stoma-mouth)
Ancylostoma duodenale
(?) whose name literally means the “American murderer” (Latin necator-murderer)
Necator americanus
o identified in specimens obtained from Texas, USA, it is believed that it actually originated in Africa
Necator americanus
Small cylidrical worms were observed in diarrheic stool of some French soldiers repatriated from Cochin-China (referring to Vietnam), thus, earliest cases were decribed as Cochin-China diarrhea.
These were named Strongyloides stercoralis (strongylus- round, eidosresembling, stercoralis-fecal).
Common Name: Giant intestinal roundworm
A. Ascaris lumbricoides
1
(?) live in the lumen of the small intestine.The female worm produces both fertilized and unfertilized eggs which are passed out in faeces.
Adult worms
2
A female may produce approximately (?) eggs per day
200,000
3
In the (?), the fertilized egg embryonates. Larvae develop to third stage within fertile eggs after 2 to 3 weeks in moist, warm, shaded soil
soil
4
Humans become infected by ingestion of the ?
embryonated eggs
5
the (?) hatch
larvae
6
the (?) invade the intestinal mucosa, and are carried via the portal, then systemic circulation on to the heart, then into the lungs
larvae
7
The (1) break out of the capillaries into the alveoli. The (2) mature further in the lungs (10 to 14 days), after a (3), penetrate the alveolar walls, ascend the bronchial tree to the throat, and are swallowed
- larvae
- larvae (L4s)
- molt
They develop into (1) in the small intestine, where they worms maintain their position due to their body muscle tone, spanning the lumen,
and exerting pressure against the walls of the small intestine.
Between 2 and 3 months are required from ingestion of the (2) to oviposition by the adult female.
(3) can live 1 to 2 years.
- adult worms
- Infective eggs
- Adult worms
Clinical manifestations of ascariasis are caused by the pulmonary migratory phase of (?) in the small intestine and the wandering adult worms.
the larvae, the adult worms
The (?) causes allergic reaction.
larval migration
The initial exposure to (?) during the lung migration phase is usually asymptomatic, except when the larval load is heavy.
larvae
One may experience symptoms referable to respiratory system such as ?
asthmatic respiration, cough with bronchial rales and chest pain.
These symptoms may be due to the (?) and massive destruction of the lung parenchyma as the larvae break through the capillaries on their way to the alveolar sacs,
petechial hemorrhages
In massive infection, the hemorrhage may give rise to ?.
Ascaris pneumonitis
In hypersensitive individuals, even a few larvae may give rise to allergic eosinophilic infiltration of the lung called ?.
Loeffler’s syndrome
The pulmonary clinical features subside in ? after infection
1 or 2 weeks
Due to larval migration in the blood stream, the larvae may lodge in vital organs such as the ?.
brain and spinal cord, the eyeball and the kidney
Cosmopolitan but is more widely distributed in tropical and subtropical countries with warm and moist soil.
A. Ascaris lumbricoides
Over a billion of people are infected globally.
A. Ascaris lumbricoides
Infection rates are highest in children.
A. Ascaris lumbricoides
It co-exists with Trichuris trichiura.
A. Ascaris lumbricoides
In many countries, the Philippines included, the prevalence may reach 80-90% in certain high risk groups like public elementary school children.
A. Ascaris lumbricoides
Fecal-oral route.
A. Ascaris lumbricoides
Infection occurs in humans when the embryonated eggs containing the infective third-stage larvae are swallowed in soil-contaminated food.
A. Ascaris lumbricoides
The population most at risk of contracting Ascaris lumbricoides infection is children who place their contaminated hands into their mouths.
A. Ascaris lumbricoides
Sources of contamination range from children’s toys to the soil itself.
A. Ascaris lumbricoides
This often occurs in areas where poor sanitation practices are common, such as open defecation or using night soil as fertilizer for vegetables.
A. Ascaris lumbricoides
House flies and cockroaches can serve as mechanical vectors.
A. Ascaris lumbricoides
The embryonated eggs can survive in moist shaded soil for a few months to about 2 years in tropical and subtropical areas, but for much longer in temperate regions.
A. Ascaris lumbricoides
Resistance of Ascaris eggs to chemicals is almost legendary.
A. Ascaris lumbricoides
They can embryonate successfully in 2% formalin, in potassium dichromate, and in 50% solutions of hydrochloric, nitric, acetic, and sulfuric acid, among other similar inhospitable substances.
A. Ascaris lumbricoides
(?) is the primary species involved in human infections globally, but Ascaris derived from pigs (often referred to as A. suum) may also infect humans.
Ascaris lumbricoides
Formerly called Oxyuris vermicularis.
B. Enterobius vermicularis
Common Names: Pinworm, seatworm.
B. Enterobius vermicularis
In United Kingdom and Australia, threadworm is used, which is also used to refer to ?
Strongyloides stercoralis.
1
(?) Enterobius vermicularis deposits eggs on perianal folds
Gravid adult female
2
Man acquires infection by ingesting (?) containing third-stage larva
embryonated eggs
It takes about 1 month for the female to mature and begin egg production.
B. Enterobius vermicularis
The adult life span is about two months.
B. Enterobius vermicularis
After fertilization of the female worms, the males usually die.
B. Enterobius vermicularis
Gravid female worms migrate out of the anus at night (nocturnal migration) when the anal sphincter is relaxed and the oxygen tension is decreased.
B. Enterobius vermicularis
They lay eggs that adhere to the perianal skin
B. Enterobius vermicularis
A single female lays up to 17,000 (average of 11,000) eggs per day.
B. Enterobius vermicularis
When all the eggs are laid, the female worm dies.
B. Enterobius vermicularis
When laid, each egg contains a partially developed larva, which can develop to infectivity in 4 to 6 hours under optimal conditions
B. Enterobius vermicularis
Infected individuals may reinfect themselves, known as an autoinfection, if infective eggs are ingested via hand-to-mouth contamination due to scratching of perianal area with fingers leading to deposition of eggs under the nails.
B. Enterobius vermicularis
This mode of infection is mostly common in children.
B. Enterobius vermicularis
In retroinfection, the eggs laid on the perianal skin immediately hatch into the infective stage larva and migrate through the anus to develop into worms in the cecum.
B. Enterobius vermicularis
Rarely, eggs may become airborne and be inhaled and swallowed.
B. Enterobius vermicularis
About one-third of enterobiasis or oxyuriasis are asymptomatic.
B. Enterobius vermicularis
The worm produces intense itching of the perianal area (pruritus ani) and also the perineal area, when it crawls out of the anus to lay eggs.
B. Enterobius vermicularis
This leads to scratching and irritation of the skin around the anus. and may give rise to secondary bacterial infection.
B. Enterobius vermicularis
Children infected with this parasite may suffer from insomnia due to the pruritus.
B. Enterobius vermicularis
Other signs of infection are poor appetite, weight loss, irritability, nocturnal enuresis (involuntary urination), grinding of teeth, and abdominal pain.
B. Enterobius vermicularis
Unlike the other intestinal nematodes, Enterobiasis is not associated with eosinophilia or with elevated immunoglobulin E (lgE).
B. Enterobius vermicularis
In female patients, the worms may cause ectopic migration when they crawl into the vulva and vagina causing irritation.
B. Enterobius vermicularis
It may migrate up to the uterus and fallopian tubes.
B. Enterobius vermicularis
This may cause symptoms of cervicitis, chronic salpingitis, peritonitis, and recurrent urinary tract infections.
B. Enterobius vermicularis
The worm is sometimes found in surgically removed appendix and has been claimed to be responsible for appendicitis.
B. Enterobius vermicularis
Cosmopolitan, in both temperate and tropical areas.
B. Enterobius vermicularis
Prevalence rates for Enterobius vermicularis are highest in temperate regions and also in urban areas.
B. Enterobius vermicularis
Enterobiasis is considered to be the most common helminth infection in the United States.
B. Enterobius vermicularis
In the Philippines, prevalence levels have been found to be 29% among schoolchildren from exclusive private schools, and 56% among those from public schools.
B. Enterobius vermicularis
Locally, prevalence is consistently higher in females (16%) compared to males (9%).
B. Enterobius vermicularis
The most common means of transmission is by anus-to-mouth through contaminated fingers or other objects in the mouth, or by inhalation of dust containing Enterobius eggs.
B. Enterobius vermicularis
Under cool moist conditions, the egg remains viable for about 2 weeks, but under warm, dry conditions, they begin to lose their infectivity within 2 days.
B. Enterobius vermicularis
Transmission is facilitated by factors including overcrowding, wearing soiled clothing, lack of adequate bathing and poor personal hygiene, especially among young school-aged children.
B. Enterobius vermicularis
Finger sucking and nail biting may be sources of recurrent infection in children.
B. Enterobius vermicularis
It may be transmitted through sexual activity, especially via oral and anal sex
B. Enterobius vermicularis
Enterobiasis is extremely contagious and can easily spread among members of a family or in institutions.
B. Enterobius vermicularis
Hence, it has been described as a familial or a group disease.
B. Enterobius vermicularis
Humans are the only natural host for Enterobius vermicularis
B. Enterobius vermicularis
Two (2) species of hookworms are human parasites:
- Necator americanus - Ancylostoma duodenale
Common Names:
o (1): New world hookworm
o (2): Old world hookworm
- Necator americanus
- Ancylostoma duodenale
1
? are passed in the stool
Eggs
2
under favorable conditions (moisture, warmth, shade), (?) hatch in 1 to 2 days and become freeliving in contaminated soil
larvae
3
These released (1) larvae grow in the feces and/or the soil , and after 5 to 10 days (and two molts) they become (2) larvae that are infective
- rhabditiform (first-stage)
- filariform (third-stage)
4
These (1) can survive 3 to 4 weeks in favorable environmental conditions On contact with the human host, typically bare feet, the (2) penetrate the skin and are carried through the blood vessels to the heart and then to the lungs.
They penetrate into the pulmonary alveoli, ascend the bronchial tree to the pharynx, and are swallowed
- infective larvae
- larvae
5
The (1) reach the jejunum of the small intestine, where they reside and mature into adults.
(2) live in the lumen of the small intestine, typically the distal jejunum, where they attach to the intestinal wall by means of well-developed mouth parts (cutting plates in N. americanus and teeth in A. duodenale)
- larvae
- Adult worms
Most adult worms are eliminated in 1 to 2 years, but the longevity may reach several years ((1) - 4 to 20 years; (?): 2-7 years).
- N. americanus
- A. duodenale
A (?) lays about 25,000-30,000 eggs in a day and some 18- 54 million during its life time.
single female worm
Some (?), following penetration of the host skin, can become dormant (hypobiosis in the intestine or muscle).
A. duodenale larvae
These (?) are capable of re-activating and establishing patent, intestinal infections.
larvae
In addition, infection by A. duodenale may probably also occur by the oral route, when (1) of A. duodenale are swallowed and develop into (2) in the intestine without migrating through the lungs, and the transmammary route.
- mature filariform larvae
- mature worms
Hookworm disease (necatoriasis or ancylostomiasis) manifests three main phases of pathogenesis:
o the invasion or cutaneous period
o the migration or pulmonary phase
o the intestinal phase.
This begins when filariform larvae penetrate skin.
Invasion or cutaneous phase C. Hookworm species
They do little damage to superficial layers, since they seem to slip unbroken skin through hair follicles, or pores.
Invasion or cutaneous phase C. Hookworm species
The usual sites of infection are the dorsum of the feet or between the toes; also on the hands, especially interdigital spaces.
Invasion or cutaneous phase C. Hookworm species
Once in the dermis, however, their attack on blood vessels initiates a tissue reaction.
Invasion or cutaneous phase C. Hookworm species
If, as it usually happens, pyogenic bacteria are introduced into skin with the invading larva, a severe local itching known as ground itch, dew itch, or coolie itch will result.
Invasion or cutaneous phase C. Hookworm species
Erythematous papular rash develops when a large number of larvae penetrate the skin.
Invasion or cutaneous phase C. Hookworm species
This is a self-limiting condition, lasting for 2 to 4 weeks.
Invasion or cutaneous phase C. Hookworm species
This occurs when larvae break out of the lung capillary bed into alveoli and progress up bronchi to the throat.
Migration or pulmonary phase C. Hookworm species
Each site hemorrhages slightly, with serious consequences in massive infections; however, very large numbers of larvae migrating through the lungs simultaneously are rare.
Migration or pulmonary phase C. Hookworm species
The phase is usually asymptomatic, although there may be some dry coughing and sore throat.
Migration or pulmonary phase C. Hookworm species
A pneumonitis and Loeffler’s syndrome may occur in heavy larvae infection.
Migration or pulmonary phase C. Hookworm species
Intestinal hookworm infections are commonly asymptomatic.
Attachment of the worms to the mucosa with their strong buccal capsule and teeth or cutting plates may stimulate abdominal pain, nausea, and anorexia.
Intestinal Phase C. Hookworm species
Adult worms suck blood aided by the anticoagulant that they secrete.
Intestinal Phase C. Hookworm species
The worms change feeding sites and the old biting sites will continue to bleed.
Intestinal Phase C. Hookworm species
Blood loss per worm is about 0.03 ml per day for N. americanus and about 0.15-0.25 ml per day for A. duodenale.
Intestinal Phase C. Hookworm species
Thus, in heavy infection, a substantial amount of blood can be lost, and a severe irondeficiency (microcytic, hypochromic) anemia may develop in a short time.
Intestinal Phase C. Hookworm species
Nevertheless, a moderate hookworm infection will gradually produce an iron-deficiency anemia as body reserves of iron are used up.
Intestinal Phase C. Hookworm species
Patients have reported vague gastrointestinal disturbances and eosinophilia (sometimes referred to as Wakana syndrome) following peroral infection.
Intestinal Phase C. Hookworm species
