Flow and storage in groundwater systems

The dynamic nature of groundwater is not readily apparent, except where discharge is focused at springs or where recharge enters sinkholes. Yet groundwater flow and storage are continually changing in response to human and climatic stresses. Wise development of groundwater resources requires a more complete understanding of these changes in flow and storage and of their effects on the terrestrial environment and on numerous surface-water features and their biota.     

Origin of Clostridium perfringens isolates determines the ability to induce necrotic enteritis in broilers

Since the ban on growth-promoting antibiotics in animal feed in the European Union, necrotic enteritis has become a major cause of mortality in broiler chickens. Despite the importance of the disease, the pathogenesis is still not completely understood. In the current study, Clostridium perfringens strains isolated from healthy flocks and isolates from outbreaks of necrotic enteritis were evaluated for the ability to cause gut necrosis in an intestinal loop model in laying hens and in an experimental infection model in broilers. High, intermediate and low alpha toxin producing strains were chosen from each isolation source. Only the isolates from field outbreaks induced necrotic gut lesions, independent of the amount of alpha toxin produced in vitro. It was also shown that alpha toxin producing isolates from calf hemorrhagic enteritis cases were not able to induce necrotic enteritis in poultry. These results suggest the presence of host specific virulence factors in C. perfringens strains, isolated from chickens with intestinal necrotic enteritis lesions.     

The risk of salmonellae shedding by dogs fed Salmonella-contaminated commercial raw food diets

Twenty-eight research dogs were enrolled to determine the prevalence of salmonellae shedding after consumption of 1 Salmonella-contaminated commercial raw food diet meal. Sixteen dogs were exposed to Salmonella-contaminated commercial raw food diets and 12 to Salmonella-free commercial raw food diets. Seven of the exposed dogs shed salmonellae 1-7 days after consumption of Salmonella-contaminated raw food diets. None of the dogs fed Salmonella-free diets shed salmonellae. No clinical signs were observed in either group. Five of the 7 dogs shed the same serotypes as those recovered from food samples used for feeding. Results showed the same serotypes and antimicrobial resistance pattern in 2 of the 7 shedders. Dogs fed Salmonella-contaminated raw food diets can shed salmonellae and may, therefore, be a source of environmental contamination potentially leading to human or animal illness.     

Viral respiratory diseases (ILT,aMPV infections,IB): are they ever under control?

Abstract1.?The use of vaccines is the main approach to control of the economically important poultry viral respiratory diseases infectious laryngotracheitis (ILT), avian metapneumovirus (aMPV) infections and infectious bronchitis (IB). This paper appraises the current methods of vaccine control in the light of the nature of each virus and epidemiological factors associated with each disease.

2.?Infectious laryngotracheitis virus (ILTV) exists as a single type with a wide range of disease severity. It is a serious disease in certain regions of the world. Recent work has distinguished molecular differences between vaccine and field strains and vaccine virus can be a cause of disease. Vaccines have remained unaltered for many years but new ones are being developed to counter vaccine side effects and reversion and reactivation of latent virus.

3.?Avian metapneumoviruses, the cause of turkey rhinotracheitis and respiratory disease in chickens exists as 4 subtypes, A, B, C and D. A and B are widespread and vaccines work well provided that accurate doses are given. Newer vaccine developments are designed to eliminate reversion and possibly counter the appearance of newer field strains which may break through established vaccine coverage.

4.?IB presents the biggest problem of the three. Being an unstable RNA virus, part of the viral genome that codes for the S1 spike gene can undergo mutation and recombination so that important antigenic variants can appear irregularly which may evade existing vaccine protection. While conventional vaccines work well against homologous types, new strategies are needed to counter this instability. Molecular approaches involving tailoring viruses to suit field challenges are in progress. However, the simple use of two genetically different vaccines to protect against a wide range of heterologous types is now a widespread practice that is very effective.

5.?None of the three diseases described can claim to be satisfactorily controlled and it remains to be seen whether the newer generations of vaccines will be more efficacious and cost effective. The importance of constant surveillance is emphasised and the testing of novel vaccines cannot be achieved without the use of vaccine-challenge experiments in poultry.     

Designing resistance management programs: How can you choose?

A list of often-discussed resistance management tactics is critically reviewed. Alteration of insecticides across generations, non-persistent formulations, and the use of pesticides conferring only low magnitudes of resistance seem to be among the most promising tactics for general use in resistance management. Justifying the first two choices usually requires little more than data on product persistence in terms of toxic effect on susceptible individuals under field conditions. The last tactic requires additional information on resistance ratios for resistant and susceptible genotypes under field exposure. The efficacy of pesticide mixtures is highly dependent on equal persistence of both compounds used in the mixture. The number of genes involved in resistance and the fitness disadvantages they may confer in the absence of use appear to be of relatively little significance in choosing management tactics.     

Effects of microbial inhibitors on the degradation rates of metamitron,metazachlor and metribuzin in soil

Rates of carbon dioxide evolution and degradation rates of metamitron, metazachlor and metribuzin were measured in two soils in the presence of three microbial inhibitors. The nonselective microbial inhibitor sodium azide reduced both carbon dioxide evolution and the rate of loss of all three herbicides in both soils, although the reduction in degradation rate of metamitron was small. The antibacterial antibiotic novobiocin enhanced carbon dioxide evolution from both soils but had variable effects on the rates of herbicide degradation. It inhibited degradation of metazachlor and metribuzin, and in one of the soils its effects on metazachlor degradation were similar to those of sodium azide. Novobiocin inhibited degradation of metamitron to a small extent in one soil only. The antifungal antibiotic cycloheximide also enhanced carbon dioxide evolution from both soils. In general, its effects on herbicide degradation were similar to those of novobiocin, although the extent of inhibition was usually less pronounced. The results are discussed in terms of the relative involvement of microorganisms in degradation of the three herbicides.     

The physical and chemical properties of the herbicide cinmethylin (SD 95481)

Cinmethylin (SD 95481), is a novel herbicide developed for the selective pre-emergence control of many annual grass weeds in a wide range of temperate and tropical crops. Representing new herbicide chemistry, cinmethylin is in the cineole family. Cinmethylin is a mobile colourless liquid with a boiling point of 313°C under an inert atmosphere at atmospheric pressure. It has a density of 1015 kg m^?3 and a viscosity of 70–90 mPa s, both at 20°C. It is miscible in all proportions with most organic solvents but has a low solubility, 63 mg litre^?1, in water. It has a vapour pressure of 10.2 mPa (20°C) and the vapour pressure/temperature relationship is given by log_e P(Pa)=28.9–9816/T (K). The n-octanol/water partition coefficient is 6850 and soil organic matter/water sorption coefficient (K_om) ranges between 165 and 235 over the three types of soil used in these studies. Cinmethylin is stable in water over the pH range 3–11. Solutions of cinmethylin in water or solvents are reasonably stable to sunlight, though thin films on a quartz surface photooxidise mainly to an ester within 24 h. This rate can be reduced by the addition of photostabilisers or by sorption onto soil surfaces. In an inert atmosphere cinmethylin is stable to high temperatures, though, in air, oxidation occurs at temperatures above 100°C to give the same product as by photodecay.     

The pyrethrins and related compounds. Part XXVIII: Alkenyl- and alkynyl-substituted benzyl esters

Over 100 benzyl esters of pyrethroidal acids were synthesised and tested for insecticidal activity to establish detailed structure–activity relationships in compounds with side-chains similar to those in the natural pyrethrins. Alkenyl, and corresponding alkynyl, side-chains were effective, both at the 3- and 4-positions, as were side-chains with extended substitution in either E or Z forms. A cyano group at the α-position increases activity if the side-chain is at C-3, but lowers it drastically if the substituent is at C-4. Similarly, methyl groups at C-2 and/or C-6 may increase activity whether the unsaturated side-chain is at C-3 or C-4, but only in the absence of an α-cyano group.