Elimination of Angiostrongylus costaricensis larvae in feces from experimentally infected Swiss mice: circadian rhythm and correlation with survival

Angiostrongylus costaricensis is a nematode which harbors mesentery arteries of rodents. In these animals, a circadian rhythm of elimination of first-stage larvae (L1) and a relation between the amount of L1 in feces and survival are unknown. We assessed fecal elimination of A. costaricensis L1 from experimentally infected Swiss mice and tried to correlate L1 elimination with survival. Thirteen Swiss mice were infected by gavage with ten A. costaricensis L3 larvae obtained from Phyllocaulis slugs. Feces were weighed at 7 a.m. and 7 p.m. starting from the 24th day post-infection until animal death. Feces sediment was examined in microscope for L1 counting. The mice were dead after a period ranging 19-61 days post-infection. Compared to diurnal samples, both feces' weight (2.3 +/- 0.7 vs. 1.8 +/- 0.5 g; P < 0.0001) and L1 total count [median 1,950 vs. 1,250; P = 0.015] were higher in feces eliminated at night. No difference was observed between diurnal and nocturnal elimination when counting L1 by gram of feces (725 vs. 650 L1/g; P = 0.821). A significant correlation was observed between survival and total number of L1 in feces (r = 0.84; P = 0.0007). This study suggests that mice experimentally infected with A. costaricensis eliminate more L1 at night due to higher fecal volume at this period. The correlation between number of L1 in feces and survival suggests a phenomenon of tolerance to A. costaricensis infection in mice with longer survival.