The contributions of host age and size to the aggregated distribution of parasites in yellow perch, Perca flavescens, from Garner Lake, Alberta, Canada.

The independent effects of host age and size on parasite abundance are examined in yellow perch from Garner Lake in east-central Alberta. Older, larger perch tend to have more species of parasites combined with larger parasite infrapopulations. Sexual size dimorphism in perch generates 2 different size classes within each age class >2+ yr, thus allowing the opportunity to separate the effects of age and size on the recruitment of parasites by perch. The abundances of Diplostomum adamsi and Bothriocephalus sp. both increase with host age, whereas the increased abundances of Crepidostomum isostomum and Raphidascaris acus in larger fish are, in part, suggestive of size-specific feeding behaviors of the host. A combination of parasites with size- and age-dependent infrapopulations results in a size-dependent increase in infracommunity size. A comparison of variance-to-mean ratios within age classes to overall variance-to-mean ratios shows that the effects of host age and size on parasite recruitment do contribute to parasite aggregation.

Bronchoalveolar leucocyte responses to trickle infections with Nippostrongylus brasiliensis in rats.

There is a need for experimental systems allowing study of host responses generated by continuous, low-level exposures to parasites. To assess the pulmonary inflammatory responses in different types of exposure to infection we used bronchoalveolar lavage (BAL). Rats sensitized by 500 Nippostrongylus brasiliensis larvae given in 20 doses over a 4-wk period (group T) and challenged with 500 larvae 33 days after the initial exposure were compared to rats initially given 1 sensitizing dose of 500 larvae (group B) and also to naive, sham-treated (group S) rats, subsequently challenged with 500 larvae. BAL performed prior to final challenge revealed markedly increased numbers of macrophages and eosinophils in group T, but there were only minor changes in numbers of these cells in group B. After final challenge, numbers of BAL macrophages and eosinophils were greater in group T than in group B, although in group B there was a rapid increase in numbers of these cells. Changes in numbers of BAL neutrophils were not correlated with previous sensitization to N. brasiliensis. Thus, there was a pronounced influx of leucocytes into the pulmonary lumen after secondary challenge in rats sensitized by repeated exposures to low doses of larvae.

Anthelmintic-induced destrobilation and its influence on calculated drug efficacy in Hymenolepis diminuta infections in rats.

Anthelmintic efficacy studies typically involve direct counts of worms remaining in the host shortly after drug treatment. Few such studies, however, have considered the phenomenon of tapeworm destrobilation when determining effective dosages. The present study reports on the frequency of drug-induced destrobilation and the subsequent regeneration of Hymenolepis diminuta in rats following treatment with niclosamide or praziquantel and its implications with respect to the apparent efficacy of these anthelmintics. Drug efficacies very similar to those reported in the literature were determined upon examination of infected animals 24 hr posttreatment. Small regenerating worms were, however, observed in the small intestine of rats 8 days after treatment, indicating that destrobilated worms were present, but overlooked, during the initial examination. Within several days posttreatment, destrobilated worms can regenerate to a size that is readily apparent in the gut contents, allowing the effective dosage to be determined with much greater confidence. Due to the demonstrated ability of these destrobilated worms to regenerate to the gravid state, it is imperative that a fully effective anthelmintic dosage be determined and administered.

Trickle infections with Nippostrongylus brasiliensis in rats: larval migration through the lungs.

The effects of exposure of rats to repeated low-level (trickle) infections with Nippostrongylus brasiliensis were assessed by measuring intestinal and lung worm burdens. Worm recoveries from the intestine, made during a period of trickle infection in rats of different ages, showed a virtually complete rejection of intestinal worms in old rats and a partial rejection in young rats. Recoveries from lungs were made in young rats after challenge infection with 500 third-stage (L3) larvae, given after a 2- or 4-wk period of sensitization, during which rats were infected with 10 or 20 doses of 25 larvae. Such trickle infections elicited a strong host response to a challenge infection, manifested by low recoveries of larvae and an increased duration of larval retention in lungs. In another group of rats sensitized by a single dose of 250 L3 larvae, the recovery of larvae from challenge infection and their clearance from the lungs were similar to these observed in rats uninfected prior to challenge. The effect of trickle infections on preintestinal stages was most pronounced and consistent in rats exposed to larvae the greater numbers of times and over the longest period.

A Survey for the Microfilariae of the Canine Heartworm, Dirofilaria immitis, in the Calgary Region of Southern Alberta.

A blood survey for the prevalence of the microfilariae of the canine heartworm, Dirofilaria immitis was conducted in the Calgary area of southern Alberta between November 1977 and August 1979. A total of 514 blood samples was examined by the modified Knott's test. All of the samples were negative for D. immitis microfilariae. Wright's stained blood smears taken from 19 animals at the Calgary Zoo also proved negative. One smear from a male two-toed sloth (Choloepus didactylus) contained sheathless microfilariae which were distinguishable from those of D. immitis. These results, as well as mail survey data indicate that D. immitis is not endemic in the Calgary area.It is recommended that the modified Knott's test be used for similar large scale sampling studies. In addition, it is suggested that the testing of both native and exotic zoo animals which could serve as definitive hosts of D. immitis be continued. These animals may become local sources of infection or introduce other species of microfilariae which will have to be differentiated from those of D. immitis.