Economic Aspects of Disease Monitoring with Special Reference to Bovine Paratuberculosis

Monte Carlo simulation models were used to evaluate the feasibility and potential results of a proposed national survey of the prevalence of bovine paratuberculosis (PTB) in dairy herds in Norway. The expected herd prevalence was assumed to be 0.2% in the simulations. Infected herds were classified as detected if 1 animal was sero-positive. With a sample size of 6000 herds at least 1 truly infected herd was detected in 99% of the iterations. The low sensitivity of the ELISA test, the assumed low herd prevalence, the typical low within-herd prevalence of PTB and the small herd sizes in Norway all present problems in detection of the disease. The results showed that the ratio between false-positive herds and true positive herds detected had a median of 70:1. At the assumed herd prevalence of 0.2% and a cost/test of 70 NOK the median cost of detecting 1 infected herd was approximately 900,000 NOK. If 2 positive reactors were needed to classify a herd "infected" the median cost of detecting 1 infected herd was 5,055,000 NOK. Our results suggest that a randomized national prevalence survey would not be feasible, due to the low probability of detecting infected herds and because of the high number of false-positive reactions that would be expected.     

Economic Aspects of Disease Monitoring with Special Reference to Bovine Paratuberculosis

Monte Carlo simulation models were used to evaluate the feasibility and potential results of a proposed national survey of the prevalence of bovine paratuberculosis (PTB) in dairy herds in Norway. The expected herd prevalence was assumed to be 0.2% in the simulations. Infected herds were classified as detected if 1 animal was sero-positive. With a sample size of 6000 herds at least 1 truly infected herd was detected in 99% of the iterations. The low sensitivity of the ELISA test, the assumed low herd prevalence, the typical low within-herd prevalence of PTB and the small herd sizes in Norway all present problems in detection of the disease. The results showed that the ratio between false-positive herds and true positive herds detected had a median of 70:1. At the assumed herd prevalence of 0.2% and a cost/test of 70 NOK the median cost of detecting 1 infected herd was approximately 900,000 NOK. If 2 positive reactors were needed to classify a herd "infected" the median cost of detecting 1 infected herd was 5,055,000 NOK. Our results suggest that a randomized national prevalence survey would not be feasible, due to the low probability of detecting infected herds and because of the high number of false-positive reactions that would be expected.

     

The Suitability of Some Algae for Mass Cultivation for Food, with Special Reference to Dunaliella bioculata

Twenty-five strains of freshwater and saltwater algae have beeninvestigated for their suitability for mass cultivation forfood. Under laboratory conditions a strain of Dunaliella bioculatahas been found to give yields comparable with those obtainedfrom Chlorella. It is suggested that only when the growing algalcells are exposed in very thin layers will the yield not belimited by light penetration. The storage polysaccharide ofD. bioculata contains a 1:4-glucosan resembling starch. Allthe essential amino-acids have been shown to be present withthe possible exception of methionine or valine and tryptophane.     

Some Effects of Light on Excised Wheat Roots with Special Reference to Peroxide Metabolism

When excised wheat roots are exposed to blue light, catalase activity changes in a way to he expected as a result of photodestruction with first order kinetics. Wheat root catalase in vivo is less light sensitive than animal catalase in vitro, possibly due to internal screening. Illumination of the roots with red light causes some increase in catalasc activity. Peroxidase activity is much less affected by light. No relation has been found between catalase destruction and chlorophyll formation. The ability of roots to oxidize pyrogallol to purpurogallin (by other workers interpreted as peroxide production) is decreased by light, especially blue light. On the contrary, one peroxide producing enzyme, glycolic acid oxidase, was detected only in roots grown in blue light. The total flavin content, or the fraction present as FAD, is not affected by light. The ascorbic acid content is low, but slightly increased by blue light.     

Some Aspects of Cobalt Metabolism by Rhodymenia palmata with Particular Reference to Vitamin B12 Content

The uptake of cobalt by Rhodymenia palmata from sea-water hasbeen studied by the use of radio-cobalt 6o. Periodic absorptionand desorption associated with illumination have been found.A dependence on carbon dioxide concentration has also been established.No effect of the addition of antibiotics to the sea-water canbe detected and no evidence of cobalt fixation as vitamin B₁₂has been obtained. Instead, another stable organic compoundof cobalt has been discovered, differing from vitamin B₁₂ inchromatographic and ionophoretic behaviour. The possible natureof the new compound is considered.     

Fruiting in Sphaerobolus with Special Reference to Light

Sphaerobolus grows and, provided there is sufficient illumination,fruits readily on oatmeal agar or on malt agar. No effect oflight on vegetative growth can be demonstrated. On the maltmedium, increased fruiting occurs with increase of nutrientup to 4 per cent, malt, but at higher concentrations fruitingis not increased and may be retarded. A chemically defined mediumwith starch as the carbon source allows fruiting, but at a lowlevel. Temperature has a profound effect on basidiocarp development;above 25 C. no fruit-bodies are normally formed although vegetativegrowth is approximately optimal at that temperature. For overallfruit-body production at 20 C, light above 100 lux is necessaryand light remains a limiting factor up to about 1, 000 lux.Under continuous light of suitable intensity, fruit-bodies continueto develop and discharge glebal-masses for many weeks. Thereis a distinct periodicity of discharge with (at 20 C.) about12 days between peaks of activity. This corresponds with thetime taken for basidiocarp initiation and development. A number of developmental stages of the basidiocarp are recognized.The final stage, glebal-mass discharge from stellately openedfruit-bodies, is indifferent to light, but all other stagesare stimulated by light. The light intensity for effective stimulationfalls during development and for the penultimate stage an intensityas low as 1 lux is effective. Only light of wave-length below500 mµ is active in overall basidiocarp development. Inthe sensitive region between 400 mµ and 500 mµ,there appear to be peaks of sensitivity around 440 mµand 480 mµ. In alternating light and darkness, simulating natural conditions,glebal-mass discharge occurs in the light periods. With a regimenof 24 hours light and 24 hours of darkness discharge is mainlyin the dark periods.     

Spermatology of Some Pycnogonida (Arthropoda), with Special Reference to a Microtubule-Nuclear Envelope Complex

The sperm cells of Nymphon leptocheles and N. rubrum are of the primitive type, which is a remarkable condition among arthropods. The motile sperm consist of a somewhat elongated head, a kind of midpiece and a long tail. An acrosome is absent. The nucleus is surrounded by longitudinally oriented microtubules running in furrows in the nuclear envelope. These microtubules are not interconnected by links or connected to the nuclear envelope; they persist in the mature sperm. No appreciable chromatin condensation takes place. The midpiece contains some unmodified mitochondria and a centriole. The tail is a simple, free flagellum. The results are in particular discussed in relation to other known microtubule-nuclear envelope complexes in sperm cells. The sperm cells of Pycnogonum littorale are, on the other hand, highly aberrant. They are unmotile, elongated cells containing a very high number (often more than 1000) of longitudinal microtubules arranged in complex patterns. Some folded membranes may represent the nuclear envelope. Other organelles are unidentificable or may be absent.     

Chemotaxis of Fungal Zoospores,with Special Reference to Aphanomyces cochlioides

Zoospores of phytopathogenic fungi accumulate at the potential infection sites of host roots by chemotaxis. The aggregated spores then adhere, encyst, germinate, and finally penetrate into the root tissues to initiate infection. Some of the host-specific attractants have already been identified. The host-specific attractants also induce cell differentiation of certain zoospores under laboratory conditions. This indicates that a signal released from the roots of the host plant guides the pest propagules for orientation and prepares them for establishing a host-pathogen relationship by necessary physiological changes. Some non-host plant secondary metabolites were found to markedly regulate behavior and viability of zoospores, suggesting that non-host compounds may also play a role in protecting the non-host plants from the attack of zoosporic fungi. We hypothesized that zoospores perceive the host signal(s) by specific G-protein-coupled receptors and translate it into responses by way of the phosphoinositide-Ca²⁺ signaling cascade. The details of the signal transduction mechanism in fungal zoospores are yet to be discovered. In this report, we review the signaling and communications between phytopathogenic fungal zoospores and host and non-host plants with special reference to Aphanomyces cochlioides.