Susceptibility and reactive manifestation to Trichinella spiralis infe
ction were studied in atypical hosts (sheep) for the period of 247 day
s. Sheep produced anti-trichinella antibodies as early on Day 11 (low
titer 1 : 200), with maximum reached at Day 35 (titer 1 : 800). From D
ay 42 the antibody level was declining with a negative result of exami
nation on Day 70. Mice exibited anti-Trichinella antibodies only on Da
y 32 (titer 1 : 200). This level was rising, reaching high titer (1 :
1 600) on Day 56. This antibody level persisted until Day 156. In the
following period, a rapid decrease in the titer was observed (Graph).
On Day 32, T. spiralis larvae in sheep were present in all groups of t
he muscles examined. The highest larval counts during the entire exper
iment were detected in the masseter. The initially high counts in the
diaphragm and tongue were reduced to only 1/4 or 1/10 at the end of th
e experiment. In mice, the larvae occurred evenly throughout the entir
e experiment (Tab. I). The first appearance of a capsule around the T.
spiralis larva in muscles was observed on Day 32 p. i. No cell respon
se was detected around the capsule (Fig. 1). Neither was any response
observed around necrotizing larvae, even though the surrounding myofib
rils were caused to die off (Fig. 2). Certain differences in the degre
e of myofibril degradation by larvae were evident as early as on Day 3
2. The least damaged myofibrils were those in the masseter, tongue and
diaphragm. This finding correlates with the histological recovery of
a different number of necrotized larvae from the individual muscle gro
ups examined. Fresh blood extravassations around larvae were observed
on Day 59 (Fig. 3). They could be caused by the migration of larvae to
a parasitation site. Live uncapsulated larvae were also found on Day
115 p. i. (Fig. 4). An increased cellular presence around some larvae
was. observed on Day 84. The larvae surrounded by lymphocytes conseque
ntly died off, those without lymphocytic responses formed capsules and
survived (Fig. 5). The necrotizing larvae were subject to a powerful
phagocytic process, presented by histiocytes, forming multinuclear sym
plasms (Fig. 6). On Day 11 p. i., larvae inside a capsule were dying o
ff as well. The initial stage of larval necrosis in a capsule is also
accompanied by an increased lymphocytic responce (Fig. 7). The conditi
on of larvae in capsules and the cellular unresponsiveness as late as
on Day 247 indicate the long-lasting viability of the larvae. The caps
ules surrounding T. spiralis larvae in mice were distinctly seen as ea
rly as on Day 32 p. i. Lymphocytic aggregations around the capsule wer
e observed throughout the entire experiment (247 days) - Fig. 8.