Economic and social factors in designing disease control strategies for epidemics on networks

Models for control of epidemics on local, global and small-world networks are considered, with only partial information accessible about the status of individuals and their connections. The main goal of an effective control measure is to stop the epidemic at a lowest possible cost, including treatment and cost necessary to track the disease spread. We show that delay in detection of infectious individuals and presence of long-range links are the most important factors determining the cost. However, the details of long-range links are usually the least-known element of the social interactions due to their occasional character and potentially short life-span. We show that under some conditions on the probability of disease spread, it is advisable to attempt to track those links. Thus, collecting some additional knowledge about the network structure might be beneficial to ensure a successful and cost-effective control.Comment: To be published in Acta Phys. Pol.

Effects of Clupein and of its Degradation Products on a Rhizobium Bacteriophage, on its Host Bacterium and on the Interaction between the two

RESP-357

The behaviour of Rhizobium bacteriophages during and after exposure to ultraviolet radiation

SUMMARY: After inactivation by ultraviolet radiation, particles of two Rhizobium bacteriophages interfered temporarily with the multiplication of active particles of the homologous phage, in liquid cultures of their respective host bacteria. Inactivated particles did not affect the number of plaques produced by active particles in bacterial cultures on agar. No evidence was found that particles that were inactive singly became active when two or more of them infected the same bacterial cell. The rate of inactivation approximated closely to that of a first-order reaction. Exposing infected bacteria to visible light increased the residual activities of irradiated phage preparations by amounts equivalent to decreasing the doses of ultraviolet irradiation by a constant factor. Exposing either the irradiated phage preparations or the bacterial cultures separately to visible light had no effect. Those ultraviolet irradiated phage particles which remained active were so altered that they became relatively unstable

The ability of single phage particles to form plaques and to multiply in liquid cultures

SUMMARY: The results of testing a bacteriophage to a strain of clover nodule bacteria using young (1 day) and old ( 5 days) bacterial cultures both fit to the hypothesis that phage multiplication can be initiated by single phage particles. As the same phage preparations gave more plaques on solid media and higher proportions of liquid cultures in which phage multiplication could be detected, with young than with old bacterial cultures, the fit to the hypothesis is not an evidence that every single phage particle will multiply. It may be so when young bacterial cultures are used, although there is no positive evidence for it. With older bacterial cultures definitely only a proportion of viable phage particles succeed in starting phage multiplication, the proportion decreasing with the increasing age of bacterial cultures used for testing

Studies on the ability of light to counteract the inactivation action of ultraviolet radiation on plant viruses

Summary: Of seven plant viruses tested, all except tobacco mosaic showed the phenomenon of photoreactivation, i.e. plants exposed to visible light after inoculation with preparations partially inactivated by ultraviolet radiation produced more local lesions than plants kept in darkness. Five strains of tobacco mosaic virus, which differed widely in their pathogenicity and other properties, were tested, but none showed the phenomenon. Of the six viruses that did, potato × showed it much the most strongly, tomato bushy stunt and a tobacco necrosis virus the least; cabbage black ringspot, cucumber mosaic and tobacco ringspot were intermediate. Photoreactivation does not occur immediately after plants are inoculated. With irradiated preparations of potato virus X, most particles need about 30 min. to reach the state in which their ability to infect is affected by light; once in this state, exposure to daylight for 15 min. gives almost complete photoreactivation. Some irradiated particles respond to light of 80 f.c., but others need brighter light; no additional response occurs when light intensity is increased above 600 f.c. The sensitive state of potato virus X persists for about 1 hr. in plants kept in darkness, after which the particles seem to be permanently inactivated. With antibodies and enzymes, a constant amount of absorbed energy decreases the activity of a unit weight by a given fraction. This rule does not apply to plant viruses, which lose infectivity with less absorbed energy than the rule predicts. If viruses are more sensitive because they contain nucleic acid, their sensitivity is not a direct function of their content of nucleic acid. Potato virus X has the same nucleic acid content as strains of tobacco mosaic virus, but is inactivated by less absorbed energy and individual strains of tobacco mosaic virus also differ by factors of two in the amount of radiation needed to decrease their infectivity by a given fraction

A study of the mechanism of inhibition of bacteriophage multiplication by chymotrypsin

RESP-331

The Effect of Infection with Bacteriophage on the Electrokinetic Potential of Rhizobium leguminosarum

SUMMARY: Infection with bacteriophage increased the electrophoretic mobility of pea nodule bacteria (Rhizobium leguminosarum) at pH 7, suggesting an alteration of the bacterial surface. This seemed to occur at about the middle of the latent period

Effect of Specific Polysaccharides from the Host Bacteria and of Ribonuclease on the Multiplication of Rhizobium Phages

SUMMARY: Two serologically unrelated strains of nodule bacteria produced two different polysaccharides, only one of which precipitated with antiserum to its parent bacterium. Both polysaccharides interfered with the multiplication of two bacteriophages in liquid cultures of the two bacterial strains, each of which was susceptible to only one of the two bacteriophages. One polysaccharide was slightly more effective than the other in interfering with multiplication of both bacteriophages: one phage was much more susceptible than the other to the interfering action of both polysaccharides. Crystallized pancreatic ribonuclease interfered with multiplication of bacteriophages much more strongly than did the polysaccharides. Neither the polysaccharides nor ribonuclease destroyed the phage particles