Trichinella spp.
Severe muscle infections
Classic Case: Trichinellosis
Middle-aged male presents with a fever (38.5°C for one week), significant fatigue, chills, headache, terrible muscle aches and pains, and swelling around the eyes. He is an avid hunter, and eats his home-prepared meat. Labs show elevated eosinophils.
Causative Agent of:
- Trichinosis
- Also known as Trichinellosis
- Multiple species:
- T. spiralis is the classic species
- T. murrelli, nativa, britovi also
Physical Features
- Helminth
- Nematode
- Small: 1-2 mm long
Epidemiology
- World-wide: Various species of Trichinella
- U.S.: 26 cases in 2016 (CDC; MMWR)
- Often seen in small clusters
- People who ate same animal meat
Reservoir and Hosts
- N. America:
- Many wild animals
- Bear, boar, moose, cougar, walrus
- Globally: Pigs
- (In N. America, pigs are screened)
Transmission and Risk Groups
Transmission:
- Ingestion of undercooked meat that contain larvae
Risk Groups:
- World-wide: Consumption of undercooked pork
- U.S.: Usually hunters, consumption of wild game
- Undercooked (or smoked)
Life Cycle
- Cyst ingested, degraded by pepsin/gastric acid in stomach
- Releases larvae into sm intestine, larvae invade mucosa
- Males + females mate, survive 4 weeks, make ~1500 larvae
- Larvae penetrate intestine, spread thru blood/lymphatics
- Larvae invade/encyst in active, striated skeletal muscle cells
- Here, Trichinella forms a “Nurse Cell”: a protective cyst
- Mature nurse cell: distinct from all other cell types
- Can survive for the entire life of host
- Ingestion of infected muscles by another animal continues cycle
T. spiralis, larval cyst
Trichinella sp., Summary
T. spiralis muscle cysts
Clinical
TrichinosisSymptoms
- Incubation period: 3-7 days
- Prodrome (GI phase):
- Gastroenteritis, diarrhea, nausea
- Classic Signs (Systemic Phase):
- Myalgia, muscle weakness, rashes common
- Conjunctivitis, upper eyelid edema,
- Splinter hemorrhages in fingernails
- Usually occur 1-2 weeks after prodrome
- A biphasic illness
Complications
- Death: Rare, but can occur 3-6 days after serious symptoms
- Myocarditis: Most common parasitic cause of myocarditis
- Larvae do not encyst in cardiac muscle
- Due to eosinophil-induced inflammatory myocarditis
- CNS involvement (meningitis/encephalitis)
- Primary or secondary pneumonia
Pathogenesis
- GI Phase:
- Larvae in GI tract, mate, produce larvae
- Larvae penetrate GI lining = GI symptoms
- Muscle/Systemic Phase:
- Larvae migrate through body tissues
- Encyst in muscle = damage/inflammation
- Causing muscle/systemic symptoms
Diagnosis
- Serology: anti-Trichinella IgGs seen by 3 weeks post-infection
- Most common test for suspected cases
- Tissue Biopsy: Microscopic detection of encysted larvae
- Heavily infected people: 50+ larvae/gram of muscle
- Invasive, and infrequently used, but is also definitive Dx
- Patient History: Consumption of undercooked meat
- Lab Findings: Eosinophilia
- Most cases, as early as 2 weeks post-infection
- Elevated creatine kinase, aldolase, LDH
- (Muscle tissue damage)
Prevention
- Cook meat (Pork, wild game)
- U.S. commercial pork is screened
- T. spiralis: killed at -20°C for 3-5 days
- But other sp. of Trichinella are freeze-resistant
- Humans are a “dead-end” host
Treatment
- Albendazole, mebendazole
Splinter hemorrhages, Trichinella
T. spiralis muscle cysts
Trichinella Conjunctivitis
T. spiralis, larval cyst
References
- The CDC on Trichinella sp.
- Epidemiology, Diagnosis, Treatment, and Control of Trichinellosis. 2009. Clin. Microbiol. Rev. 22:127.
- Biology and Genome of Trichinella spiralis. In: Wormbook, The online review of C. elegans biology. 2006.
- Clinical aspects of infection with Trichinella spp. 1996. Clin. Microbiol. Rev. 9:47.