Virus, bacteriophages and water purification

Water can be a vector of viral disease, but direct virological analysis of water has logistic and practical limitations. Viruses of major importance for water hygiene (e.g. hepatitis and gastro-enteritis viruses) cannot yet be grown in tissue culture. Therefore, as in bacteriological quality procedures, model organisms are required for the evaluation of virological quality of water and the effectiveness of virus removal by water treatment processes. On the basis of published information, the F specific RNA (FRNA) phages have been chosen for this purpose. For the enumeration of the phages a particular Salmonella typhimurium strain with an artificially introduced F plasmid was developed as a host strain and was found to give accurate and reliable results. FRNA phages were found in very high numbers (10(2)-10(5) pfu/ml) in all types of waste water investigated. FRNA phages are seldom found in non-faecally contaminated waste water. Surprisingly low numbers are found in faeces. FRNA phages in waste water effluent were found to be highly resistant to chloramines and relatively resistant to UV inactivation. The FRNA phages can thus effectively be used as indicator organisms for human pathogenic viruses in the evaluation of disinfection processes for water treatment plants.     

The effectiveness of in‐plant chlorination in poultry processing

1. Sampling carcasses after plucking or after the post‐evisceration spray‐wash showed that 10 or 20 ppm available chlorine in the processing‐plant water supply caused little reduction in carcass contamination.

2. When 20 ppm chlorine was used in the water supply to parts of the processing‐plant other than the mechanical immersion chilling system, counts of faecal and spoilage bacteria from carcasses were reduced approximately 10‐fold after passage through the chilling system; bacterial numbers were correspondingly decreased in the chiller water due to a carry‐over of chlorine from the final spray‐washer.

3. Artificial contamination of carcasses with a readily identifiable strain of Escherichia coli confirmed the occurrence of cross‐contamination during plucking and evisceration; in‐plant chlorination reduced neither the proportion of carcasses contaminated nor the numbers of organisms transferred at these stages.

4. In most cases the chlorine‐resistance of poultry spoilage pseudo‐monads was greater than that of E. coli; hence in‐plant chlorination is to be recommended for processing‐plant water supplies which carry such spoilage organisms.     

Some characteristics of four attenuated vaccine virus strains and a virulent strain of Aujeszky's disease virus

Summary

In the present study four attenuated virus strains, used as vaccines, and a virulent strain of Aujeszky's disease virus (AD V) were compared with respect to their virulence in mice, their ability to induce virus‐specified thymidine kinase (TK) in infected cells, and their cleavage profiles of viral DNA's after treatment with the restriction endonuclease Kpnl.

The survival time of mice inoculated with the B‐KAL or the virulent NIA‐3 strain was comparable. whereas the Hanha and BUK strains required significantly loniser periods to kill mice. Mice were resistant to the MK‐25 strain of ADV.

The strains were assayed for TK phenotype by plaque autoradiography after ³H‐thymidine labelling of infected cells. MK‐25 proved to be the only strain defective in induction of TK in pig kidney cells. Restriction endonuclease analysis of viral DNA's revealed that each vaccine strain showed a characteristic fragment pattern that could easily be differentiated from that of other vaccine and field strains of ADV. The present results demonstrate that the mouse virulence lest and the TK assay detect differences in biological properties of ADV strains, but that restriction endonuclease analysis is required for unambiguous identification of vaccine and field strains of ADV.     

Isolation and identification of bacteriophages infecting ayu Plecoglossus altivelis altivelis specific Flavobacterium psychrophilum

In order to investigate methods for controlling systemic bacterial coldwater disease (CWD), bacteriophages that infect Flavobacterium psychrophilum were isolated by the enrichment method from pond water collected from Japanese ayu farms. The five phages isolated were classified as members of Myoviridae (PFpW-3, PFpC-Y), Podoviridae (PFpW-6, PFpW-7), and Siphoviridae (PFpW-8) and had highly variable patterns of infectivity for different F. psychrophilum isolates (n = 128). The stability tests of the phages in different waters, pHs and temperatures were assessed, and the results indicated that none of the phages were affected by ayu farm conditions. Among the phages, PFpW-3 had high infectivity for F. psychrophilum isolated from ayu and other fish and demonstrated sufficient survivability in the stability tests. Thus, PFpW-3 and its indicator strain N2-3 were inoculated into cytophaga broth at different doses of multiplicity of infection (MOI) and proved to be efficient for the reduction of bacterial growth. This study may be the basis for a further evaluation of phage therapy in the treatment of CWD in Japanese ayu farms.     

The control of lymphoid leukosis in a flock White Plymouth Rock chickens

Summary

Lymphoid leukosis (LL) was successfully controlled in a commercial basic breeding line of White Plymouth Rock chickens. The control method has been developed for breeder flocks and consists of three elements: - In the flock under study, homogenates of embryos from all eggs collected during a number of I4‐day periods are tested for the presence of LL viruses.

- Only eggs from hens that have been shown not to shed virus in their eggs are used for the production of progeny. The offspring are reared in isolation during the first two months of life, at which time the age‐related resistance against tumour formation by LL viruses appears to be sufficiently developed.

- The chickens are subsequently inoculated intramuscularly with LL viruses of subgroups A and B transferred to a conventional chicken house.

The vaccination raises a solid immunity to horizontal LL virus exposure and, due to the age‐related resistance, tumour formation does not follow.

No excretion of LL viruses could be detected in three generations of White Plymouth Rock chickens to which the three elements of the control procedure were applied. Clinical disease was not observed in any of the chickens under notice.     

Performance of Medicago sativa under dryland conditions on the eastern Highveld

Abstract

Increased livestock numbers and improved animal performance based on dryland lucerne pastures requiring little or no nitrogenous fertilizer have been demonstrated to be feasible on the eastern Highveld. With large scale planting of lucerne‐based pasture (25% of arable land) 350 to 500% more sheep products can be delivered at a lower cost. When lucerne is included in crop rotations the production cost of grain can also be reduced. The increased usage of lucerne‐based pastures, especially for sheep and dairy enterprises, will also reduce the pressure on natural pasture and improve the conservation of vegetation, soil and water resources.     

A new bacteriophage of Corynebacterium glutamicum isolated from swine waste

A bacteriophage for Corynebacterium glutamicum strain LP-6 was isolated from swine waste. It belongs to the Siphoviridae family or Bradley morphologic group B, has a narrow host range, and is sensitive to chloroform and resistant to carbon tetrachloride. The phage is unstable (96% inactivation) in swine waste stored for 4 months at 22 C. The DNA has a molecular weight of approximately 20 Md, cohesive ends, and numerous restriction endonuclease sites. The phage differs from other known C glutamicum phages.     

Absorption,distribution and residue evaluation of active substances used as feed additives

Summary

Administration of feed additives is based on the necessity of satisfying a need in human nutrition. Oral feed additive intake results in an equilibration level which is followed by a steady state after absorption. The equilibrium point of the blood (tissue) level can be calculated mathematically. 70 Per cent of the plateau of the steady state is reached within four times the half‐life.

Some compounds give rise to an ‘initial peak’ with higher concentrations than the expected plateau level (phase of adaptation). For residue evaluation these effects have to be considered. The relevance of different metabolic processes and the impact on a traditional monofactorial evaluation, neglecting the incidence of combination, is mentioned. Commonly used residue assessment is discussed and the safety margin of a toxicological threshold elucidated.     

Errata

Summary

Netobimin was tested for efficacy against Haemonchus contortus using 7 groups of 5 parasite‐free lambs of six month age. The lambs in group 1 and 2 were infected with 10,000 larvae of a benzimidazole susceptible strain and those in groups 3–7 with the same dose of a resistant strain. The following treatment scheme was applied 21 days after infection: lambs in groups 2 and 4 ‐ 7.5 mg kg^‐1 netobimin, in group 5 ‐ 20 mg kg^‐1 netobimin, in group 6 ‐ 5 mg kg^‐1 oxfendazole and in group 7 ‐ 3.8 mg kg^‐1 albendazole. The lambs in groups 1 and 3 remained untreated. All lambs were slaughtered 28 days after infection. Egg counts decreased in all lambs after treatment, but increased again in lambs in groups 4, 6 and 7. There was a slight increase in lambs in group 5, while those in group 2 remained negative. Post‐mortem worm counts showed a reduction of 99.8 per cent in lambs in group 2 compared to those in group 1. In lambs in group 4–7 the reduction of worm counts was respectively 40.9, 89.5, 24.7 and 40.7 per cent compared to those in group 3. Egg development assays carried out 20 days after infection showed an average LD₅₀ of 0.46 mg ml^‐1 thiabendazole for the resistant strain. After treatment (day 27) the LD₅₀ was 0.53, 0.48, 0.58, 0.56 and 0.47 in lambs in the groups 3–7. It is concluded that netobimin and other (pro) ‐benzimidazoles should not be used in cases of benzimidazole resistance and that levamisole, pyrantel tartrate or ivermectin are preferable.     

Heredity of navicular disease

Summary

Bone structure, nutrient canals, form and definition, and a total evaluation of both fore navicular bones were radiologically evaluated in 169 three‐ and four‐year‐old Dutch warmblood mares divided into eleven daughter (half sister) groups. On the basis of the ‘total evaluation’, differences between the three‐and four‐year‐old horses were detectable. Using the ‘total evaluation’, significant differences were found between daughter groups consisting of three‐year‐oldmares. These differences support the theory that podotrochleosis may be (partly) due to the presence of genetic factors. The possibilities concerning selection are presented. The results of the radiological evaluation of the stallion do not have predictive value as far as his progeny is concerned.     

Highly cited article published in the veterinary quarterly in 1991

Summary

In early 1991, the Dutch pig industry was struck by the so‐called mystery swine disease. Large‐scale laboratory investigations were undertaken to search for the aetiological agent. We focused on isolating viruses and mycoplasmas, and we tested paired sera of affected sows for antibodies against ten known pig viruses. The mycoplasmas M. hysonoviae, M. hyopneumoniae, and Acheloplasma laidlawii, and the viruses encephalomyocarditis virus and porcine enterovirus types 2 and 7 were isolated from individual pigs. An unknown agent however, was isolated from 16 of 20 piglets and from 41 of 63 sows. This agent was characterized as a virus and designated Lelystad virus. No relationship between this virus and other viruses has yet been established. Of 165 sows reportedly affected by the disease, 123 (75 per cent) seroconverted to Lelystad virus, whereas less than 10 per cent seroconverted to any of the other virus isolates or to known viral pathogens. Antibodies directed against Lelystad virus were also found in pigs with mystery swine disease in England, Germany, and the United States. We conclude that infection with Lelystad virus is the likely cause of mystery swine disease.     

The introduction of expert systems in animal husbandry

Summary

The intensive nature of modern animal husbandry has changed the environmental conditions, so that protection against diseases, especially those caused by secondary pathogenic organisms, becomes an increasing concern. Production inefficiencies become more and more important. Because of their complex nature, many associated problems cannot be solved by farmers alone. With the introduction of information technology in the form of expert systems, new possibilities emerge for maximal productivity and animal health.

Expert systems are a new type of computer programmes which are able to handle problems in limited domains at an expert level, using expert knowledge and reasoning processes, within strictly defined problem limits. Expert systems as they presently exist have the following components: a knowledge base (rule‐ and data‐base), inference engine (deductive mechanism), user‐interface (explanatory facilities, etc.).

The application of knowledge engineering in animal husbandry may result in improvements in the general health and productivity of the herd and the financial returns of the farm, derived from the improved managerial control. At the same time the use of knowledge engineering may lead to greater understanding of the various epidemiological factors that influence farm results, either positively or negatively.     

Pathogenicity of two strains of Newcastle disease virus in the grey‐breasted helmet guinea fowl

Summary

Thirty‐five 6‐week‐old guinea fowl keets, seronegative for maternal antibodies to Newcastle disease virus, were infected with Hens strain (33/56) and Kumarov strain of Newcastle disease virus intramucularly (IM) or intranasally (IN).

Clinical signs were first noticed four days post infection (PI) in the group infected al but five days PI in the group infected IN with Hens strain of Newcastle disease virus. These clinical signs were similar in both groups and included anorexia, droopiness, huddling together, greenish diarrhoea and marked cachexia. Prominent nervous signs, including spasms of the head and neck, were observed in groups infected with Hens strain.

The major gross lesions observed were emaciation with prominent keel bone, empty intestinal tract and distended gall bladder in most keets.

The histological lesions were characterised by meningoencephalitis, necrosis and loss of lymphocytes from splenic and lymphoid aggregates. There was muscular degeneration and necrosis in the gizzard and mild pulmonary congestion and oedema in some keets.

Neither gross or microscopic lesions were observed in keels that had received the Kumarov strain.     

Preliminary clinical pharmacological investigations of tylosin and tiamulin in chickens

Summary

The minimal inhibitory concentrations (M1C) of tiamulin and tylosin for mycoplasma. Gram‐positive, and Gram‐negative micro‐organisms isolated from chickens were determinated by the agar dilution method. Median M1C values for tiamulin against Mycoplasma gallisepticum (0.05 μg/ml) and Mycoplasma synoviae (0.10 μg/ml) were 2 to 4 times lower than the corresponding values for tylosin. Tiamulin was also slightly more effective in vitro in inhibiting Escherichia coli, Pasteurella multocida, and beta‐haemolytic streptococci than was tylosin. Groups of chicken were offered tiamulin medicated drinking water at rates of 125 and 250 mg/litre for 48 hours. Average serum tiamulin concentrations were 0.38 and 0.78 μg/ml, respectively. When tylosin tartrate was added to the drinking water at 500 and 700 mg/litre, average serum drug levels were 0.12 and 0.17 μg/ml, respectively.

Tiamulin was 45% bound in chicken serum, as against 30% serum protein binding or tylosin. Correlations were made between free (non protein bound) serum drug levels and the MIC values of the two drugs. Such comparisons suggest that when tiamulin is given in the drinking water at rates of 125 to 250 mg/litre, better antimycoplasmal activity is to be expected in vivo than by giving tylosin tartrate in the drinking water at 500 to 700 mg/litre. Based on these data, no clinical efficacy of these dose rates can be expected in flocks infected by gram‐negative microorganisms such as E. coli or P. multocida. The tylosin tartrate rate of 500 to 700 mg/litre, may be clinical ineffective the treatment of Staphylococcus aureus infections.     

Hyperadrenocorticism in four cats

Summary

This paper describes four cats with hyperadrenocorticism. Cat 1 showed polydipsia and polyphagia. Diabetes mellitus was initially diagnosed As the animal appeared to be insulin resistant, pituitary and adrenocortical function tests were performed and the diagnosis of hyperadrenocoricism was made. Resistance to the high‐dose dexamethasone suppression test was noticed in this cat. Pathological examination revealed a pituitary chromophobe adenoma.

Cat 2 presented with diabetes mellitus, which was treated with insulin. The animal had a pendulous abdomen and its coat was in a poor condition. The low‐dose dexamenthasone suppression test demonstrated hyperadrenocorticism. Necropsy findings of pituitary tumour and hyperplasia of the adrenal cortex confirmed the diagnosis.

Cat 3 showed clinical abnormalities indicative of hyperadrenocorticism, for instance, muscle weakness, alopecia, multiple abcesses. The diagnosis of hyperadrenocorticism was confirmed by the results of the lowe‐dose dexamethasone suppression test. Pathological examination revealed an adrenocortical carcinoma.

Cat 4 presented with polydipsia. The cause of this symptom was not found initially. One and a half years later additional symptoms, such as nephritis and polyphagia developed Hyperadrenocorticism was diagnosed because of a palpable mass cranial to the left kidney. The diagnosis was confirmed by the results of the lowe‐dose dexamethasone suppression test and the necropsy findings     

Bacteriophages as antimicrobial agents against major pathogens in swine: a review

In recent years, the development of antibiotic resistant bacteria has become a global concern which has prompted research into the development of alternative disease control strategies for the swine industry. Bacteriophages (viruses that infect bacteria) offer the prospect of a sustainable alternative approach against bacterial pathogens with the flexibility of being applied therapeutically or for biological control purposes. This paper reviews the use of phages as an antimicrobial strategy for controlling critical pathogens including Salmonella and Escherichia coli with an emphasis on the application of phages for improving performance and nutrient digestibility in swine operations as well as in controlling zoonotic human diseases by reducing the bacterial load spread from pork products to humans through the meat.     

Determination of Phylogenetic Relationships of Flavobacterium psychrophilum (Flexibacter psychrophilus), Flavobacterium columnare (Flexibacter columnaris), and Flexibacter maritimus by Sequence Analysis of 16S Ribosomal RNA Genes Amplified by Polymerase Chain Reaction

Abstract

The nearly complete small subunit 16S ribosomal RNA (rRNA) gene sequence amplified by polymerase chain reaction was determined for Flavobacterium psychrophilum (formerly Flexibacter psychrophilus) by using automated nucleotide sequencing. The sequence was found to be 1,465 base pairs (bp) in length, a size consistent with previously determined sequences for 14 other bacterial species from various taxa, including the yellow-pigmented bacteria. Sequence signatures confirmed that this organism was a member of the bacterial division Bacteroides–Flavobacterium. Parsimonious and additive phylogenetic trees were constructed with homology, and pairwise evolutionary distances were used to estimate phylogenetic relationships. Data show that F. psychrophilum, F. columnare, and Flexibacter maritimus are closely related, have a common descent, and represent a distinct group within the division Bacteroides–Flavobacterium. This group also included other organisms from the genera Flavobacterium and Cytophaga. Further, Flavobacterium aquatile, the type species for the genus Flavobacterium, was also determined to be a member of this “Flavobacterium–Cytophaga–Flexibacter subcomplex.” This supports previous assertions that the type strain of Flavobacterium should be changed to a more representative species such as Flavobacterium breve.     

Inclusion keratoconjunctivitis ('pink eye') in sheep

Summary

The cytoplasnwtic inclusion bodies, which, in 1931. Coles discovered in the corneal cet. of sheep suffering from contagious keratoconjunctivitis arc now considered to be the reticulate bodies of a chlamydia. Colesiota conjunctivae (synonym: Chlamydia psittaci ovis).

According to the postulates of Koch Colesiota conjunctivae is a primary cause of contagious kerato‐conjunctivitis in sheep, but the clinical picture is complex and is a result of the interaction between the infecting chlamydiae. host resistance factors. and secondary infections caused by opportunistic bacterial ocular pathogens.

The clinical syndrome might also be caused by other micro‐organisms, such as Mycoplasma conjunctivae or environmental factors, such as dust. However, in these cases, cytopiasnwtic inclusion bodies cannot be found in the corneal cells of diseased eyes.

To differentiate chlamydial keratoconjunctivitis from keratoconjunctivitis due to other causes, it is proposed to include in the name the laboratory findings typical for this disease: Sheep Inclusion Keratoconjunctivitis.

Chlamydia are Gram‐negative bacteria, which arc obligate intracellular parasites.

Prolonged treatment seems to be required to eradicate chlamydiae from a host and antibiotics must reach intracellular levels that are higher than their minimum inhibitory concentration for chlamydiae. Tetracyclines are the drugs of choice. This means that for a microbiological cure, diseased sheep must be injected several times a day for a week or more. Because the disease is usually self‐limiting and economic losses are considered low, this seems unnecessary and control of the disease by local treatment of secondary infections .seems sufficient.

However, this will not prevent .spreading of the disease in a herd and relapses may occur.     

Haematology and blood‐chemistry for predicting abscesses and other abnormalities in slaughtered pigs

Summary

Blood values of slaughtered pigs were determined in an attempt to relate the blood profile with the prevalence of abscesses. To this end 319 pigs were selected and grouped into classes on the basis of pathological ante‐ and post‐mortem findings. The classes thus distinguished were (i) no pathology, (ii) pleurisy or pneumonia and (iii) abscesses occurring singly, metastasised or in combination with other abnormalities.

By stepwise discriminant analysis it was established that the blood variables ln(fibrinogen) and albumin were particularly suitable for the detection of abscesses in slaughtered pigs. In this way a correct classification of 89.3% of affected pigs is possible. The numbers of false‐positives and false‐negatives were 19.3% and 10.7%, respectively.

For meat‐inspection purposes application of blood analyses is promising. For application in meat‐inspection practice rapid on‐line methods need to be devised.