Trichinelosis Flashcards
Trichinella spiralis has 4 subspecies:
Trichinella spiralis spiralis- cosmopolitan
Trichinella spiralis nelsoni -afrucan predators and scavenger
Trichinella spiralis nativa- arctic polar bears
Trichinella spiralis pseudospiralis- birds and mammals
Where does the adult form live ?
Duodenal and jejunal mucosa of flesh eating mammals
Infectious Larval form lives??
In striated muscles of carnivorous and omnivorous mammals
Describe epidemiology of trichinella spiralis
Cosmopolitan more in Us than in tropics and orient
Associated with pork consumption
Adult worm lives buried in SI mucosa of pig rat or man
Also polar bears in arctic account for outbreaks
Estimates
1.5 m American carry trichinella cysts in their musculature
150k to 300k new infections annually
Morphology
One of the smallest nematodes
Females 3-4mm
Males- 1.4-1.6mm, have tail end pappilae - claspers - hold onto female when mating
Larvae :80um
Classification of female Trichinella based on egg/larvae laying
Viviparous- release 1st stage larva in SI
Adult life span of Trichinella is short. Explain
Male dies after fertilizing females
Females die after discharging larvae- approx 16 weeks
Life cycle
- sylvatic cycle
- domestic cycle
Enteric stage- ingestion of meat that contains encysted larvae> larvae released into small intestine> mature into adults in the small intestine where fecund female produce first stage larvae
Systemic/migratory stage- larvae penetrate the gut, enter lymphatics and then circulation via thoracic duct.
Diagnostic/ infective stage - larvae enter striated muscle ( extraocular, tongue, deltoid, PECS, gastrocnemius) > larvae molt, encyst and develop into infective third larvae within the 15 days
Where does the encystment happen?
Where muscles attach to tendons
And superficially in bulky muscle
T/F: only a single cycle of trichinella occurs in one host
True
For continuation of the cycle and maintenance of species, infection needs to be transmitted to another host. Same or different species
T/F: salting, smoking and drying destroys larval forms
False
Prolonged freezing decontaminates trichinella
True (20days)
T/F : man is the dead end host of the parasite
True
T/F: larvae kills all cells they enter except striated muscle
True
How long does it take the larvae to encyst
20 days after entry of the larvae into the muscle cell
Nurse cell
First muscle cell invaded
Muscles invaded most frequently are??
Have low glycogen levels and are relatively active.
Extraocular muscles of the eye
Tongue
Jaw
Deltoid , pectoral
The diaphragm
Gastrocnemius
Cysts in trichinella
Are formed by tissue reaction around encapsulated larvae.
Ovoid approx 400 by 250um
May calcify in 2 years but remains viable even in calcified cysts
T/F : the cysts lie longitudinally ALONG muscle fibres
True
Most common muscle used for biopsies
Deltoid
Clinical features of trichinella
- Enteric phase- penetration of host intestinal mucosa
- Larval migration - migratory phase - muscle invasion
- Intramuscular encystment
Enteric phase-
2-30 hrs after ingestion
Presents as acute food poisoning
Larval migration/ migratory phase
1-4 weeks after infection
Pneumonia, splinter hemorrhages, facial edema neurological symptoms
Intramuscular encystment
Difficulty swallowing
Dyspnea-
Myocarditis
Respiratory arrest
Lethal trichinosis
Splinter hemorrhages
Under Fingernails
Lab diagnosis
Clinical observation and eosinophilia
Positive history of pork consumption
Serological test - ELISA, western blot,
Muscle biopsy - digest with pepsin and examine trichinoscope
Brachman intradermal test
Molecular test - PCR
Lethal trichinitis
Combines myocarditis, encephalitis, meningitis and pneumonitis
Respiratory arrest
Heavy invasion and muscle destruction of diaphragm
Treatment
Anthelmintic not effective for newborn or maturing larvae
Corticosteroid and mebendazole ( within 2 weeks of eating contaminated meat or GI symptoms) for severe illness
Prevention
Cook meat to temperature of 55°c or higher education on pork transmission from pork and bear meat
Avoid rats in piggery
Avoid feeding garbage or pork scrabs to pigs
Meat and pork inspectors in abbatoirs
Irradiation of packaged meat
Heavy infection
Approx 1000 cysts / gram of muscle
