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Trichinella spiralisPresented by: Lauren Hannan and Chloe Jensen

Taxonomy

Kingdom: Animalia

Phylum: Nematoda

Class: Adenophorea

Order: Trichurida

Family: Trichinellidae

Genus: Trichinella

Species: T. spiralis

Introduction

Trichinella spp. is the smallest nematode parasite of humans, which has the most unusual life cycle, and is one of the most widespread and clinically important parasites in the world Worlds largest intracellular parasite

T. spiralis is actually several strains – 8 “sibling species” are recognized No morphological differences among the different

kinds of Trichinella

Geographic distribution: worldwide

Morphology

Males are about 1.4 mm – 1.6 mm long, and are flat anteriorly and posteriorly Have a large copulatory pseudobursa

on each side

Females are about twice the size as males Vulva is found near the esophagus The single uterus of the female is filled

with developing eggs in the posterior portion, while the anterior portion contains the fully developed juveniles.

Hosts

Definitive Carnivorous and omnivorous animals, such as pigs

or bears

Intermediate hosts Primarily rodents

Accidental hosts Humans

Life cycle

Trichinellosis is acquired by ingesting meat containing cysts (encysted larvae) of Trichinella

Once larvae enter the stomach and are exposed to digestive enzymes such as gastric acid and pepsin, the larvae burst out of the cysts and invade the small intestine, where they develop into adults Live for about 4 weeks in the small intestine

After 1 week, females release larvae that migrate to the striated muscles and encyst – alter gene expression of the host cell! Complete encystment takes about 4-5 weeks Encysted larvae can remain viable for several years

Life cycle continued

Life cycle traditionally considered to be two epidemiologically distinct types: a domestic (involving pigs and rats, around human habitation), and a sylvatic (involving wild animals)

Rodents are primarily responsible for maintaining the endemicity of this infection Carnivorous/omnivorous animals, such as pigs or bears,

feed on infected rodents or meat from other animals

Humans become accidentally infected when eating improperly processed meat of these animals (or when eating food contaminated with such meat)

Pathogenesis

Causes Trichinosis

Three stages of pathogenesis: Stage 1: penetration of adult females into the mucosa:

12 hours – 2 days after infection Low grade infection Worms migration in intestinal epithelium causes:

Traumatic damage to the host tissues Inflammation Nausea, vomiting, diarrhea, Sweating Respiratory difficulties Red skin blotches

Stage ends with facial edema and fever

Pathogenesis Continued

Stage 2: migration of juveniles: Damages blood vessels, creating:

Localized edema Pneumonia, pleurisy Encephalitis, meningitis, nephritis, peritonitis Deafness, brain/eye damage Sublingual hemorrhage

Death from myocarditis may occur Don’t stay in the heart, migrate through causing

necrosis and infiltration of leukocytes

Pathogenesis Continued

Stage 3: Juvenile penetration of muscle fibers: Symptoms are varied and vague

Intense muscle pain Difficulty breathing/swallowing Masseter muscle swelling Weakening pulse and blood pressure, heart damage Various nervous disorders

Death by heart failure, respiratory complications, and kidney malfunction

Heavy infection causes: Reduced heart muscle contraction Reduced stress, work, and power output

Diagnosis

Most cases go undetected

Routine exams rarely detect juveniles

Muscle biopsy is the most accurate form of diagnosis Digestion of the muscle in artificial gastric enzymes

for several hours

Treatment

No treatment

Just relieve symptoms Analgesics and corticosteroids Purges during beginning symptoms can dislodge

worms

Thiabendazole Effective in animals Human trials have been variable

Control

Cook pork and meats properly and freeze unused meat

Watch out for “backyard butchering”

Don’t used uncooked garbage for pig food

Keep pig pens clean

Proper hygiene and sanitation

Review

What is the geographic range of this parasite?

What kind of hosts are humans?

T/F: Males are larger than females

After the larvae leave the small intestine, where do they migrate to? How long can they survive there?

What is the treatment method?

Name a control method

What is the most effective diagnosis method?

How does death typically occur?