Page 105 - Medical Parasitology_ A Textbook ( PDFDrive )

98 10 Nematodes: Roundworms

Encysted larva in i = Infective Stage
striated muscle
d = Diagnostic Stage

i
Domestic 1
Cycle Ingestion of
undercooked meat
Meat scraps/
Cannibalism 1
i

Larva released in
Encysted larva in small intestine
striated muscle 2

Sylvatic
Cycle
Predation/
scavenging Encysted larva 3
in striated muscle
d 5 Circulation Adults in small
intestine
4 Larva deposited
in mucosa

Fig. 10.13 Life cycle of Trichinella spiralis (Reproduced from https://www.cdc.gov/dpdx/trichi-
nellosis/index.html)

Muscle invasion occurs after the release of larvae by the female worm at 1–4
weeks of infection. They migrate to the muscle and finally encapsulated in striated
muscles. During the migration phase, patients may present with fever, facial oedema,
periorbital swelling, myalgia and weakness of affected muscles. Eosinophilia is
common. They can infect cardiac muscles causing myocarditis but they do not
encyst. They can cause encephalitis but do not encyst in the brain. Myocarditis and
encephalitis are serious complications and can be fatal.
Stage of encapsulation last for 1–8 months after infection. Fever and other symp-
toms subside at this stage. After this stage, calcification of the cyst occurs. The clini-
cal manifestations are self-limiting. Human is a dead-end host.
Diagnosis
1. Muscle biopsy of the infected muscle
Detection of encysted larvae in muscle tissue.