Comparison of arithmetic and geometric means as measures of a central tendency in cattle nematode populations

Efficacy calculations in anthelmintic studies require estimates of the central tendency for the nematode populations. Confusion exists among practitioners regarding which measures of central tendency are most appropriate; although the arithmetic mean is frequently used, there are theoretical reasons for preferring the geometric mean. To investigate this controversy, arithmetic and geometric means were compared for their suitability for use in measuring efficacy. Arithmetic and geometric means were compared as measures of central tendency for skewed distributions. The following criteria were developed to facilitate the comparison: (1) probability around the parameter, (2) influence of extreme values, and (3) proximity to the median. Under log-normality, theoretical results demonstrated the superiority of the geometric mean. Modified-bootstrap simulations using empirical data from cattle were used to confirm theoretical expectations. Simulations on log-normal data supported the geometric mean as the better indicator of the central tendency. Additionally, for data not confirmed as log-normal, the superiority of geometric means was demonstrated. In a comparison of precision, it was shown that mean squared error was always smaller for sample geometric means than for arithmetic means when n> or =2. Simulation results added support to that conclusion.     

Comparative efficacy of an injectable vaccine and an intranasal vaccine in stimulating Bordetella bronchiseptica-reactive antibody responses in seropositive dogs

OBJECTIVE: To compare antibody responses to intranasal and SC Bordetella bronchiseptica vaccines in seropositive dogs. DESIGN: Randomized controlled study. ANIMALS: 40 young adult Beagles vaccinated against B bronchiseptica. PROCEDURE: Dogs were randomly assigned to 1 of 4 groups (intranasal vaccine, SC vaccine, intranasal and SC vaccines, no vaccine) and vaccinated on day 0. Serum and salivary B bronchiseptica-reactive antibody responses were measured on days 0 through 7, 10, 14, 21, and 28. RESULTS: Dogs that were vaccinated with the SC vaccine, alone or in combination with the intranasal vaccine, had a significant increase in serum concentration of B bronchiseptica-reactive IgG beginning on day 5 and persisting through day 28. Dogs that were vaccinated with the intranasal vaccine alone had a significant increase in serum concentration of B bronchiseptica-reactive IgG beginning on day 10 and persisting through day 28, but serum IgG concentration in these dogs was significantly less than concentration in dogs that received the SC vaccine. Neither vaccine had a demonstrable effect on salivary concentrations of B bronchiseptica-reactive IgA or IgG. On day 10, all vaccinated groups had significantly higher serum IgA concentrations than did unvaccinated control dogs. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that the SC B bronchiseptica vaccine may be used to stimulate antibody responses in seropositive dogs. There was no apparent benefit to administering these vaccines simultaneously. Intranasal vaccines may not be effective for booster vaccination of dogs previously exposed to or immunized against B bronchiseptica. Dogs should be vaccinated at least 5 days prior to exposure to B bronchiseptica.     

From trees to fleas: masting indirectly affects flea abundance on a rodent host

Mast seeding causes strong fluctuations in populations of forest animals. Thus, this phenomenon can be used as a natural experiment to examine how variation in host abundance affects parasite loads. We investigated fleas infesting yellow-necked mice in beech forest after 2 mast and 2 non-mast years. We tested 2 mutually exclusive scenarios: (1) as predicted by classical models of density-dependent transmission, an increase in host density will cause an increase in ectoparasite abundance (defined as the number of parasites per host), versus (2) an increase in host density will cause a decline in flea abundance (“dilution,” which is thought to occur when parasite population growth is slower than that of the host). In addition, we assessed whether masting alters the relationship between host traits (sex and body mass) and flea abundance. We found a hump-shaped relationship between host and flea abundance. Thus, the most basic predictions are too simple to describe ectoparasite dynamics in this system. In addition, masting modified seasonal dynamics of flea abundance, but did not affect the relationship between host traits and flea abundance (individuals with the highest body mass hosted the most fleas; after controlling for body mass, parasite abundance did not vary between sexes). Our results demonstrate that pulses of tree reproduction can indirectly, through changes in host densities, drive patterns of ectoparasite infestation.     

Growth factor messenger ribonucleic acid expression during differentiation of porcine embryonic myogenic cells

The growth factors, IGF-I and II, their binding proteins, IGFBP, and members of the transforming growth factor (TGF) superfamily (myostatin and TGFbeta1) are known to regulate proliferation and differentiation of myogenic cells. We hypothesized that changes in the relative expression of members of the IGF and TGFbeta systems play a significant role in regulating myogenesis in porcine embryonic myogenic cell (PEMC) cultures. Therefore, determining the expression patterns of these factors during PEMC myogenesis is important. Consequently, we used real-time PCR to explore the pattern of IGF-I; IGF-II; IGFBP-2, -3, and -5; IGF-type-I receptor; myogenin; myostatin; and TGFbeta1 mRNA expression during PEMC myogenesis. The progression of differentiation was assessed using creatine kinase activity and myogenin mRNA expression. As anticipated, creatine kinase activity was low in PEMC cultures at 48 h and increased 20-fold (P < 0.0001) between 48 h and its peak at 144 h. Similarly, myogenin mRNA was low at 48 h and increased approximately 5-fold (P < 0.0001) as differentiation progressed, peaking at 120 h and decreasing at 144 h. The patterns of IGF-I and IGFBP-2 mRNA expression were similar and were relatively lower in 48-h PEMC cultures, increasing approximately 5-fold (P < 0.0001) to their greatest levels at 120 h. In contrast, IGF-II and IGFBP-5 mRNA levels were relatively high at 48 h, peaking at 72 h, and steadily decreasing by 60 and 80%, respectively (P < 0.001), at 144 h. The level of IGF-type-I receptor mRNA was relatively high until 96 h of culture, after which it decreased 40% (P < 0.01), reaching a low at 144 h. Levels of IGFBP-3 mRNA were relatively high at 48 h, dropped approximately 40% to their lowest level at 72 h (P < 0.001), and then increased approximately 60% (P < 0.001) to their greatest levels at 144 h. Levels of TGFbeta1 mRNA decreased approximately 30% (P < 0.0001) between 48 and 96 h, then quickly rebounded to a peak at 120 h, and by 144 h had dropped to the levels seen at 72 h. Myostatin mRNA was at its greatest level at 48 h and declined rapidly between 72 and 96 h, finally decreasing by approximately 80% at 144 h (P < 0.0001). Our data demonstrate that these factors are differentially regulated during PEMC myogenesis and provide new information about their pattern of mRNA expression in cultured porcine muscle cells.     

Thrombostasin isoform frequency in a Central Texas field population of the horn fly, Haematobia irritans

Thrombostasin is an anti-thrombin factor that plays a role in successful feeding of the horn fly, Haematobia irritans. It has been isolated and characterized from saliva, and polymorphisms in the gene coding sequence have been previously reported. In the present study, the thrombostasin gene was analyzed from 60, field-collected flies from Camp Stanley, Texas and the allele and genotype frequencies were compared with previously published data for an Alabama field collection and a Texas in vitro colony-reared collection. Significant differences in genotype frequency and extent of genotypic diversity observed between the Alabama and Camp Stanley field collections may be attributable to host genetic differences. In addition, bull calves that were phenotyped as either high- or low-carriers were parasitized by horn flies that displayed a significantly different genotype distribution, supporting a possible explanation for horn fly host selection behavior, as evidenced by thrombostasin sequence analysis of 95 additional horn flies collected from respective hosts.     

A general model for designing networks of marine reserves

There is debate concerning the most effective conservation of marine biodiversity, especially regarding the appropriate location, size, and connectivity of marine reserves. We describe a means of establishing marine reserve networks by using optimization algorithms and multiple levels of information on biodiversity, ecological processes (spawning, recruitment, and larval connectivity), and socioeconomic factors in the Gulf of California. A network covering 40% of rocky reef habitat can fulfill many conservation goals while reducing social conflict. This quantitative approach provides a powerful tool for decision-makers tasked with siting marine reserves.