The relationship between fecundity and adult body weight in Homeotherms

Summary Bythotrephes cederstroemii Schoedler, a predatory freshwater zooplankter (Crustacea: Cladocera), was first found in the Laurentian Great Lakes in December 1984. The first individuals were from Lake Huron, followed in 1985 with records from Lakes Erie and Ontario. By late August, 1986 the species had spread to southern Lake Michigan (43°N). Bythotrephes has not previously been reported from North America, but has been restricted to a northern and central Palearctic distribution. Its dramatic and widespread rise in abundance in Lake Michigan was greatest in offshore regions. Bythotrephes appears to be invading aggressively, but avoiding habitats presently occupied by glacio-marine relict species that became established in deep oligotrophic North American lakes after the Wisconsin glaciation. Because it is a voracious predator its invasion may lead to alterations in the native zooplankton fauna of the Great Lakes. It offers the chance to study how invading plankton species join an existing community. Judging from its persistence and success in deep European lakes, Bythotrephes may now become a permanent member of zooplankton communities in the Nearctic.     

Transplantation of adult Trichinella spiralis between hosts: worm survival and immunological characteristics of the host--parasite relationship.

A technique for the transplantation of Trichinella spiralis worms directly into the host intestine is described. Infections established by the direct transfer of adult worms were essentially normal both in terms of their survival and reproduction and in their stimulation of, and susceptibility to, host immune responses. Worms transplanted from NIH mouse donors at intervals after infection had an equal ability to survive in the recipient, even when taken from the donor shortly before or during the process of worm expulsion, showing that expulsion does not require worms to be irreversibly damaged. It was noted, however, that after 7 days in the donor the ability of the worm to reproduce in the recipient was temporarily impaired.     

Trichinella spiralis: an intracellular parasite in the intestinal phase.

Trichinella spiralis has been examined by electron microscopy after fixation in situ in the intestine of mice. The worms lie within the cytoplasm of cells of the intestinal mucosa and may occupy both absorptive and goblet cells. They cause little damage to host cells. A few worms have been seen protruding from tissue by SEM techniques. These unusual observations suggest that the nematodes may be capable of exit and reentry into the epithelium.     

Trichinella spiralis and Strongyloides ratti: immune interaction in adult rats.

The consequences of prior and concurrent infection with two species of nematodes were studied in rats. Primary infection with Strongyloides ratti adversely affected the development of a secondary Trichinella spiralis infection. Both immediate and delayed challenge with T. spiralis, following the expulsion of the previous S. ratti infection, reduced the percentage of worm recovery of the former as well as their fecundities and lengths. It is suggested that nonspecific inflammation produced by one species, during the peak period of worm expulsion, was not responsible for the accelerated rate of expulsion of the other; instead a direct, specific cross-immunity was probably operative affecting the survival of the challenge species. The response elicited by previous experience of the intestinal phase was reciprocal, but there was evidence of an enhancing effect by the muscle larval stages of T. spiralis on S. ratti. Rats concurrently infected with both species expelled S. ratti more rapidly than T. spiralis. Possible mechanisms underlying the interaction between the two species are suggested and discussed.     

Trichinella spiralis: selective intestinal immune deviation in the rat

In rats, infections with 100-2000 Trichinella spiralis muscle larvae lead to a prompt immunity that is expressed in parasite expulsion within 14 days. Rats infected with more than 2000 larvae display impaired immunity with rejection delayed by 50% (7 days) or more. Suppression is selective for expulsive immunity as the antifecundity response of rats is directly proportional to dose and is expressed sooner in heavily infected subjects. Suppression of intestinal expulsive immunity was suggested by the fact that, with low doses (2000 larvae or less), worm rejection was inhibited by cortisone, whereas cortisone inhibited antifecundity but had no discernable effect on worm rejection in high-dose infections. Evidence for local immune deviation as opposed to systemic immunosuppression was obtained in experiments using parabiotic rats. When one partner was infected with 6000 worms and the other with 200, the rat infected with 200 parasites showed earlier rejection than was seen in single controls infected with 200 worms. The prolonged survival of high-dose adults was not accompanied by a change in the site of worm residence in the gut. Immunological parameters such as serum antibody levels, the number of activated cells or specific anti-T. spiralis lymphocytes in thoracic duct lymph were all increased in a dose-dependent manner. These experiments therefore demonstrate a novel autoprotective mechanism by which adult T. spiralis selectively reduce the expression of expulsive immunity in the gut.     

Lethality of disrupted intestinal lamina propia cells for Trichinella spiralis in vitro.

The possible direct role of inflammatory cells in resistance to Trichinella spiralis was studied by observing the effects of lamina propria cells from the small intestine (LP cells) of immunized rats on various stages of the parasite. Effects produced by physically disrupted cells were compared to those produced by intact cells on worms exposed to phytohemagglutinin or immune serum. LP cells were isolated from the rat intestine by collagenase digestion of everted gut segments that were previously denuded of epithelium by treatment with hyaluronidase. Disrupted cells, but not intact ones, selectively killed T. spiralis juvenile and adult worms in vitro, whereas larvae were unaffected by similar treatment. Attempts to identify the lethal component of disrupted cells led to an evaluation of the enzyme, peroxidase. Mucosal peroxidase is localized in LP cells and its activity increases several-fold during intestinal trichinosis. It is presumed to be myeloperoxidase, a particulate-bound enzyme of myeloid-derived leukocytes that functions as part of a potent antimicrobial system in combination with H2O2 and a halide. Results indicated that the vermicidal component of LP cells was associated with the pellet fraction of disrupted centrifuged LP cells, but was not linked to a peroxidase-H2O2-halide system.     

Tyvelose and protective responses to the intestinal stages of Trichinella spiralis

The unusual sugar tyvelose is the immunodominant portion of the major larval glycoprotein antigens of Trichinella spiralis, which play an important role in generating immunity against the intestinal stages of infection. The possibility that the tyvelose component itself may have a host- or parasite-protective role in the intestine was tested by following the outcome of challenge infections in mice primed and boosted with tyvelose-BSA, or in mice primed with tyvelose-BSA before boosting with larval antigen. Although antibody responses were raised against tyvelose there was no evidence of protective immunity against the intestinal stages, as assessed by total adult worm recovery or by size and fecundity of female worms in immunized mice. Equally, priming with tyvelose-BSA before boosting with larval antigen had no effect on the expression of immunity against a challenge infection. The predominant antibody isotype recorded in all immunized mice was IgG1, suggesting the induction of type 2 T cell responses, and this was confirmed by cytokine analysis, mesenteric node lymphocytes of all mice showing production of IL-5 but not IFN-gamma. Clearly immunization with tyvelose had no significant effect on T cell polarization. The data show that, with the experimental design employed, there was no evidence for a functional role of tyvelose in either host- or parasite-protection during the intestinal phase of infection.     

Villous atrophy and expulsion of intestinal Trichinella spiralis are mediated by T cells.

The development of villous atrophy and crypt hyperplasia in, and expulsion of nematodes from, the small intestine of the mouse during Trichinella infection is shown to be mediated by T cells. During Trichinella infection, worms initially localise in the anterior half of the small intestine. Their expulsion from here after 6–8 days follows the onset of villous atrophy and crypt hyperplasia in the jejunum and the normal jejunal morphology is restored after complete expulsion of worms from the small intestine at 12–15 days. In thymectomised mice, according to the extent of T-cell depletion, worm localisation is atypical, expulsion is either delayed or absent, and villous atrophy and crypt hyperplasia are either delayed and reduced or absent. The adoptive immunization of infected thymectomised mice with mesenteric lymph node cells (including primed T blasts) from infected donors completely restores the normal host response and enhances the onset of crypt hyperplasia. These findings are discussed in relation to T-cell traffic and delayed-type hypersensitivity in the gut.     

Trichinella spiralis in an agricultural ecosystem. II. Evidence for natural transmission of Trichinella spiralis spiralis from domestic swine to wildlife

Epidemiological investigations of an outbreak of trichinellosis were carried out in a domestic swine herd and it was established that the parasite also occurred in rats, and in skunks, opossums, and raccoons. Because considerable uncertainty exists regarding the role of sylvatic trichinellosis as a reservoir for the synanthropic cycle, studies were conducted to determine the genetic nature of the various isolates from this ecosystem. Pig infectivity trials, isoenzyme analyses, and repetitive DNA sequence analyses were performed. The results showed that all isolates from the farm environs were genetically similar and that they are related to Trichinella spiralis isolated from domestic pigs. The implication of these findings, in contrast to studies on isolates from wildlife elsewhere, is that this parasite is transmitted from domestic swine to sylvatic hosts and that any control or eradication efforts must take into account the potential for reinfection of hogs from wild animals.     

The genetic analysis of F1 hybrid larvae between female Trichinella spiralis and male Trichinella britovi

Hybrids between female Trichinella spiralis and male Trichinella britovi were constructed. Then, hybrid genotype was characterized by DNA markers including mitochondrial cytochrome c oxidase subunit I (CO I) gene, the gene encoding the 43-kDa excretory–secretory (ES) protein, and genomic DNA fragments specific for T. spiralis and T. britovi identified from random amplified polymorphism DNA (RAPD). PCR-restriction fragment length polymorphism (PCR-RFLP) analysis of the mitochondrial CO I gene revealed that all hybrids carried a T. spiralis pattern. The same analysis of the gene encoding the 43-kDa ES protein showed that each hybrid carried both T. spiralis and T. britovi gene type simultaneously. In the analysis of genomic DNA using RAPD-derived PCR primers, some hybrids carried T. spiralis and T. britovi-specific RAPD markers, while others carried the RAPD marker of T. spiralis only.     

Trichinella spiralis in an agricultural ecosystem. III. Epidemiological investigations of Trichinella spiralis in resident wild and feral animals

As part of a larger epidemiological study examining the transmission of Trichinella spiralis in an agricultural ecosystem, resident wild and feral animals were trapped to determine the extent of their involvement in the natural, on-farm cycling of the parasite among swine. During a 21-mo-study, seven of 15 skunks (Mephitis mephitis), one of three opossums (Didelphis virginiana), two of two feral domestic cats and a raccoon (Procyon lotor) were found to be infected, while five shrews (Blarina brevicauda) and 18 deer mice (Peromyscus spp.) were uninfected. Most of the former hosts probably became infected by scavenging dead infected swine or rats (Rattus norvegicus). However, infections obtained through predation of living rats, particularly with regard to the cats, cannot be excluded. Our observations do not suggest that there was transmission of T. spiralis from the wild animals to swine. Therefore, transmission of T. spiralis appeared to occur only from the farm's swine and rats to the associated wild and feral animals.     

Ultrastructure, antigenicity, and histochemistry of stichocyte granules of adult Trichinella spiralis.

The stichosome of adult Trichinella spiralis was studied to determine its ultrastructural, antigenic, and histochemical characteristics. Stichocytes of adult worms had 2 types of granules, type I and type II, the ultrastructure of which was different from those of muscle larvae. Both types of granules consisted of a membrane surrounding a homogeneous matrix, and type I granules were rounder than type II granules. Sera from C3H mice immunized against excretory-secretory products of muscle larvae produced positive immunostaining of type I but not type II granules. Differences in antigenicity were observed between larval and adult stichocyte granules; monoclonal antibodies against alpha-granules of muscle larvae failed to label the adult granules. Azan staining revealed a histochemical difference between larval and adult stichocytes; adult stichocytes stained yellow, whereas larval stichocytes are known to stain red or blue. Thus, the present contribution revealed the existence of 2 distinct types of stichocyte granules in adult T. spiralis and showed them to differ profoundly from those characterized previously in muscle larvae.     

Immunity to Trichinella spiralis VI. The specificity of the immune response stimulated by the intestinal stage.

Mice were immunized to the intestinal stage of T. spiralis by using infections terminated with methyridine before production of newborn larvae had commenced. The muscle larvae which encysted following a normal complete challenge infection were reduced by 87 and 95% in immunized mice. No statistically significant reduction in a challenge infection of intravenously injected parenteral larvae was produced (8% and 15% actual reduction). Previous work has shown that adult worms in a challenge infection are stunted and expelled earlier as well as having a reduced fecundity; it is concluded that the immunity generated by the intestinal stage is largely specific in its action to that phase in a challenge infection.