Helminth infections in Apodemus sylvaticus in southern England: interactive effects of host age, sex and year on the prevalence and abundance of infections
Jm. Behnke et al., Helminth infections in Apodemus sylvaticus in southern England: interactive effects of host age, sex and year on the prevalence and abundance of infections, J HELMINTH, 73(1), 1999, pp. 31-44
Helminth parasites were studied in the wood mouse, Apodemus sylvaticus, in
southern England in September of each of four successive years (1994-1997).
Nine species of helminths were recorded: five nematodes (Heligmosomoides p
olygyrus, Syphacia stroma, Pelodera strongyloides, Trichuris muris, Capilla
ria murissylvatici), two cestodes (Microsomacanthus crenata, Taenia taeniae
formis) and two trematodes (Corrigia vitta, Brachylaemus recurvum). In tota
l, 134 mice were examined and 91.8% carried at least one species of helmint
h. The majority of mice carried two to three species (60.5%) and the highes
t combination was six of the nine species recorded in the study. The patter
ns of between-year variations in the prevalence and abundance of infection
were different for each of the six species for which sufficient quantitativ
e data were available to enable statistical analysis. For H, polygyrus, the
most important source of variation arose from between-year differences, ho
st age and. the interaction of these factors: abundance increased with host
age but in 1995 the age pattern was markedly different from that in the re
maining years. The abundance of C. vitta also varied significantly between
years but additionally there was a strong independent age effect. For M. cr
enata, the year x age interaction was significant, indicating that abundanc
e among different age cohorts varied from year to year but there was also a
weak significant main effect of age arising from the youngest age cohort c
arrying no parasites and the oldest age cohort the heaviest infections. For
P, strongyloides the only significant factor was between-year variation wi
th 1995 being a year of exceptionally low prevalence and abundance of infec
tion. No significant between-year variation was detected for S. stroma but
there was a strong sex effect (males carrying heavier infections) and an ag
e effect (older mice of both sexes carrying heavier infections). The abunda
nce of Trichuris muris varied only in relation to host age, worm burdens gr
owing in intensity with increasing age, but there was also a significant in
teraction between year and host sex with respect to prevalence. For the rem
aining three species, the prevalence of infections was too low (<8.2%) to e
nable any meaningful interpretation. This analysis emphasizes the need for
carefully controlled statistical procedures in aiding the interpretation an
d the prioritization of the factors affecting worm burdens in wild rodents.