Milk Fever Control Principles: A Review

Three main preventive principles against milk fever were evaluated in this literature review, and the efficacy of each principle was estimated from the results of controlled investigations. Oral calcium drenching around calving apparently has a mean efficacy of 50%–60% in terms of milk fever prevention as well as prevention of milk fever relapse after intravenous treatment with calcium solutions. However, some drenches have been shown to cause lesions in the forestomacs. When using the DCAD (dietary cation-anion difference) principle, feeding rations with a negative DCAD (measured as (Na + K) – (Cl + S)) significantly reduce the milk fever incidence. Calculating the relative risk (RR) of developing milk fever from controlled experiments results in a mean RR between 0.19 and 0.35 when rations with a negative versus positive DCAD are compared. The main drawback from the DCAD principle is a palatability problem. The principle of feeding rations low in calcium is highly efficient in milk fever prevention provided the calcium intake in the dry period is kept below 20 g per day. Calculating the relative risk (RR) of developing milk fever from controlled experiments results in a very low mean RR (between 0 and 0.20) (daily calcium intake below versus above 20 g/d). The main problem in implementing the low-Ca principle is difficulties in formulating rations sufficiently low in calcium when using commonly available feeds. The use of large doses of vitamin D metabolites and analogues for milk fever prevention is controversial. Due to toxicity problems and an almost total lack of recent studies on the subject this principle is not described in detail. A few management related issues were discussed briefly, and the following conclusions were made: It is important to supply the periparturient cow with sufficient magnesium to fulfil its needs, and to prevent the dry cows from being too fat. Available information on the influence of carbohydrate intake, and on the effect of the length of the dry period and prepartum milking, is at present insufficient to include these factors in control programmes.     

Risk of Infection with Leishmania spp. in the Canine Population in the Netherlands

The dog is the main reservoir of Leishmania infantum, the causative agent of visceral leishmaniasis (VL) in humans in Southern Europe. In order to identify the risk of dogs from a Leishmania non-endemic area traveling to a Leishmania -endemic area becoming infected and the risk of transmitting infection to humans in non-endemic areas an investigation was performed, in which the results of a questionnaire were combined with the results of a serologic survey.     

Morpholino-mediated in vivo silencing of Cryptosporidium parvum lactate dehydrogenase decreases oocyst shedding and infectivity

Cryptosporidium is a highly prevalent protozoan parasite that is the second leading cause of childhood morbidity and mortality due to diarrhoea in developing countries, and causes a serious diarrheal syndrome in calves, lambs and goat kids worldwide. Development of fully effective drugs against Cryptosporidium has mainly been hindered by the lack of genetic tools for functional characterization and validation of potential molecular drug targets in the parasite. Herein, we report the development of a morpholino-based in vivo approach for Cryptosporidium parvum gene knockdown to facilitate determination of the physiological roles of the parasite’s genes in a murine model. We show that, when administered intraperitoneally at non-toxic doses, morpholinos targeting C. parvum lactate dehydrogenase (CpLDH) and sporozoite 60K protein (Cp15/60) were able to specifically and sustainably down-regulate the expression of CpLDH and Cp15/60 proteins, respectively, in C. parvum-infected interferon-γ knockout mice. Over a period of 6?days of daily administration of target morpholinos, CpLDH and Cp15/60 proteins were down-regulated by 20- to 50-fold, and 10- to 20-fold, respectively. Knockdown of CpLDH resulted in approximately 80% reduction in oocyst load in the feces of mice, and approximately 70% decrease in infectivity of the sporozoites excysted from the shed oocysts. Cp15/60 knockdown did not affect oocyst shedding nor infectivity but, nevertheless, provided a proof-of-principle for the resilience of the morpholino-mediated C. parvum gene knockdown system in vivo. Together, our findings provide a genetic tool for deciphering the physiological roles of C. parvum genes in vivo, and validate CpLDH as an essential gene for the growth and viability of C. parvum in vivo.     

Granule-bound starch synthase: structure, function, and phylogenetic utility

Interest in the use of low-copy nuclear genes for phylogenetic analyses of plants has grown rapidly, because highly repetitive genes such as those commonly used are limited in number. Furthermore, because low- copy genes are subject to different evolutionary processes than are plastid genes or highly repetitive nuclear markers, they provide a valuable source of independent phylogenetic evidence. The gene for granule-bound starch synthase (GBSSI or waxy) exists in a single copy in nearly all plants examined so far. Our study of GBSSI had three parts: (1) Amino acid sequences were compared across a broad taxonomic range, including grasses, four dicotyledons, and the microbial homologs of GBSSI. Inferred structural information was used to aid in the alignment of these very divergent sequences. The informed alignments highlight amino acids that are conserved across all sequences, and demonstrate that structural motifs can be highly conserved in spite of marked divergence in amino acid sequence. (2) Maximum-likelihood (ML) analyses were used to examine exon sequence evolution throughout grasses. Differences in probabilities among substitution types and marked among-site rate variation contributed to the observed pattern of variation. Of the parameters examined in our set of likelihood models, the inclusion of among-site rate variation following a gamma distribution caused the greatest improvement in likelihood score. (3) We performed cladistic parsimony analyses of GBSSI sequences throughout grasses, within tribes, and within genera to examine the phylogenetic utility of the gene. Introns provide useful information among very closely related species, but quickly become difficult to align among more divergent taxa. Exons are variable enough to provide extensive resolution within the family, but with low bootstrap support. The combined results of amino acid sequence comparisons, maximum-likelihood analyses, and phylogenetic studies underscore factors that might affect phylogenetic reconstruction. In this case, accommodation of the variable rate of evolution among sites might be the first step in maximizing the phylogenetic utility of GBSSI.      

Variation in heat-shock proteins among species of desert fishes (Poeciliidae, Poeciliopsis)

Analysis of the heat-shock proteins (hsps) of six closely related species of Poeciliopsis demonstrated the existence of biochemical diversity in the hsp100, hsp70, hsp60, and hsp30 protein families among species. Each species expressed five to seven hsp70-related isoforms. Constitutive 70-kD isoforms were identical among species, but four different patterns of heat-inducible isoforms were seen in these six species. Members of the hsp70 family of molecular chaperones are included among the most highly conserved proteins known, and the possibility of variation in hsp70 among closely related species has rarely been addressed. The hsp30 family is known to be less conserved than the hsp70 family, and, as expected, the Poeciliopsis hsp30 patterns showed more variation. Most of the hsp30 isoforms characteristic of a particular species were unique to that species. Hsp100 and hsp60 were identical in five of the species, but alternate isoforms were found in P. monacha. The small size and limited geographical distribution of the P. monacha population have probably contributed to the uniqueness of the monacha pattern. Two of the species were shown to acquire thermotolerance, the ability to withstand normally lethal temperatures when subjected to a gradual temperature increase. Rapid-heating protocols commonly used to establish critical thermal maxima of organisms do not include this inducible component of thermoresistance and therefore do not adequately assess an organism's capacity to withstand thermal stress.      

Variation in heat shock proteins within tropical and desert species of poeciliid fishes

The 70-kilodalton heat shock protein (hsp70) family of molecular chaperones, which contains both stress-inducible and normally abundant constitutive members, is highly conserved across distantly related taxa. Analysis of this protein family in individuals from an outbred population of tropical topminnows, Poeciliopsis gracilis, showed that while constitutive hsp70 family members showed no variation in protein isoforms, inducibly synthesized hsp70 was polymorphic. Several species of Poeciliopsis adapted to desert environments exhibited lower levels of inducible hsp70 polymorphism than the tropical species, but constitutive forms were identical to those in P. gracilis, as they were in the confamilial species Gambusia affinis. These differences suggest that inducible and constitutive members of this family are under different evolutionary constraints and may indicate differences in their function within the cell. Also, northern desert species of Poeciliopsis synthesize a subset of the inducible hsp70 isoforms seen in tropical species. This distribution supports the theory that ancestral tropical fish migrated northward and colonized desert streams; the subsequent decrease in variation of inducible hsp70 may have been due to genetic drift or a consequence of adaptation to the desert environment. Higher levels of variability were found when the 30- kilodalton heat shock protein (hsp30) family was analyzed within different strains of two desert species of Poeciliopsis and also in wild-caught individuals of Gambusia affinis. In both cases the distribution of hsp30 isoform diversity was similar to that seen previously with allozyme polymorphisms.      

Control of local blood flow in pulmonary inflammation: role for neutrophils, PAF, and thromboxane

The intrapulmonary instillation of C5a results in a local inflammatory response that, in this site, is accompanied by a decrease in local blood flow. Reversal of this decrease by vasodilators or the thromboxane synthesis inhibitor dazmegral has been shown to result in enhanced lung inflammation. In the present study the mechanisms underlying the decrease in flow in pulmonary inflammation were investigated in the rabbit in vivo and in the isolated blood-perfused rabbit lung. In vivo, the decrease in local blood flow was shown to be dependent on circulating neutrophils. In the isolated blood-perfused lung, inflammation induced by airway instillation of C5a was similar histologically to that seen in vivo and was also accompanied by a decrease in local blood flow. The decrease in blood flow appeared to require circulating neutrophils and was prevented by dazmegral and the platelet-activating factor (PAF) antagonists WEB 2086 and L-659,989. Furthermore, no decrease occurred in aspirin-treated lungs perfused with normal blood, suggesting that the source of thromboxane was lung rather than circulating cells. The decrease in blood flow in inflammation did not appear to be a consequence of hypoxic vasoconstriction. Inflammation in the guinea pig lung was also accompanied by a decrease in local blood flow and was also prevented by dazmegral and PAF antagonists. We conclude that local inflammation in the lung is accompanied by a decrease in blood flow that involves neutrophils and the lipid mediators PAF and thromboxane. We suggest that this form of negative feedback by the neutrophil serves to control the inflammatory response.     

Assessment of therapeutic responses to gametocytocidal drugs in Plasmodium falciparum malaria

Background

Effective mating between laboratory-reared males and wild females is paramount to the success of vector control strategies aiming to decrease disease transmission via the release of sterile or genetically modified male mosquitoes. However mosquito colonization and laboratory maintenance have the potential to negatively affect male genotypic and phenotypic quality through inbreeding and selection, which in turn can decrease male mating competitiveness in the field. To date, very little is known about the impact of those evolutionary forces on the reproductive biology of mosquito colonies and how they ultimately affect male reproductive fitness.

Methods

Here several male reproductive physiological traits likely to be affected by inbreeding and selection following colonization and laboratory rearing were examined. Sperm length, and accessory gland and testes size were compared in male progeny from field-collected females and laboratory strains of Anopheles gambiae sensu stricto colonized from one to over 25 years ago. These traits were also compared in the parental and sequentially derived, genetically modified strains produced using a two-phase genetic transformation system. Finally, genetic crosses were performed between strains in order to distinguish the effects of inbreeding and selection on reproductive traits.

Results

Sperm length was found to steadily decrease with the age of mosquito colonies but was recovered in refreshed strains and crosses between inbred strains therefore incriminating inbreeding costs. In contrast, testes size progressively increased with colony age, whilst accessory gland size quickly decreased in males from colonies of all ages. The lack of heterosis in response to crossing and strain refreshing in the latter two reproductive traits suggests selection for insectary conditions.

Conclusions

These results show that inbreeding and selection differentially affect reproductive traits in laboratory strains overtime and that heterotic ‘supermales’ could be used to rescue some male reproductive characteristics. Further experiments are needed to establish the exact relationship between sperm length, accessory gland and testes size, and male reproductive success in the laboratory and field settings.     

Opposing hemodynamic effects of substance P on pulmonary vasculature in rabbits

Substance P is a peptide implicated in the control of a variety of physiological processes. Although substance P-containing neurons impinge on the pulmonary vasculature, the effects of substance P on the pulmonary circulation have not been systematically investigated. Rabbits were anesthetized with methohexital sodium and paralyzed with pancuronium bromide. Injection of substance P (0.002-0.10 microgram/kg) in the vena cava produced dose-dependent pulmonary vasoconstriction and systemic vasodilation. Pulmonary arterial pressure reached a peak within 15-20 s and declined toward base line over 10 min. Aortic pressure fell rapidly, reaching minimum at 5-10 s. At higher doses cardiac output fell transiently, resulting in a 65% fall in pulmonary vascular conductance. If repeat substance P dosages were administered 15 min apart, there was no tachyphylaxis. Pulmonary vasoconstriction was inhibited by the cyclooxygenase blocker meclofenamate (10 mg/kg) and the thromboxane synthase inhibitor Dazmegrel (UK-38,485) (2 mg/kg). In contrast, vasoconstriction was enhanced by atropine (2 mg/kg). In Dazmegrel-treated animals in whom pulmonary vasoconstriction was established by epinephrine infusion, low doses of substance P produced vasodilation. Our findings indicate that substance P produces pulmonary vasoconstriction via prostaglandin (particularly thromboxane) generation and pulmonary vasodilation via activation of cholinergic pathways.