Polymyxin B and an antiserum against an Re mutant Salmonella typhimurium were evaluated for protective effect in an equine model of endotoxemia. Six 3- to 5-month-old foals were given endotoxin (0.25 micrograms/kg of body weight) IV after no pretreatment, or pretreatment with polymyxin B (6,000 U/kg, IV) or S typhimurium antiserum (1.5 ml/kg, IV). When given without pretreatment, endotoxin caused transient recumbency and increases in rectal temperature, and heart and respiratory rates. In addition, leukopenia and increases in circulating tumor necrosis factor (TNF) and interleukin 6 (IL-6) activities were detected. Compared with results obtained when endotoxin was given alone, pretreatment with polymyxin B resulted in significantly (P < 0.05) lower maximal plasma TNF and IL-6 activities, and significantly lower rectal temperature and respiratory rate. In contrast, compared with effects of endotoxin given without pretreatment, use of antiserum was associated with significantly (P < 0.05) higher respiratory rate, maximal plasma IL-6 activity, and total TNF response (as determined by areas under curves of plasma TNF vs time). These results indicate that polymyxin B may have potential as a treatment for equine endotoxemia. Salmonella typhimurium antiserum had no positive effect in this model, and, under certain conditions, may exacerbate the actions of endotoxin.

Epidemiologic modeling of the likely herd-to-herd transmission of pseudorabies virus (PRV) was developed to assess the progress and potential for the PRV-eradication program in the United States. The herd-to-herd transmission of PRV over a 20-year period (1993 to 2012) in the United States was simulated under various scenarios, which included variable program-funding levels and variable prevalences. A transition model (Markov process model) was used to predict yearly changes in herd prevalence of PRV infection. Five mutually exclusive states of nature for herds were assumed: uninfected and not vaccinated; uninfected and vaccinated; known to be infected and not vaccinated; known to be infected and vaccinated; and infected, but not known to be infected. Three prevalences for states in the United States were assumed: higher prevalence, moderate prevalence, and lower prevalence. Three funding levels were assumed: no eradication program, continued funding at the current level, and increased funding of 25%. Estimates made by an expert panel for determining probabilities in the state-transition matrices were used. A model also was developed, and was considered to be the most optimistic scenario likely under increased funding of 25%. The most optimistic estimates of the probabilities that still lay within the range of estimates made by the expert panel were used for this model. Only the optimistic transmission matrices allowed for total eradication of PRV. Using the optimistic matrices, all states in the United States of America had moved into the moderate- or low-level risk status by the year 2000. The longest time taken to achieve eradication was for the state of Iowa, where eradication was not achieved until 2012.

Consumption of chlortetracycline (CTC) at concentration of 220 mg/kg of feed for 4 weeks in experiment 1 and at concentrations of 110 and 220 mg/kg for 3 weeks and 440 mg/kg for 2 weeks in experiment 2 failed to eliminate streptococci-induced lymphadenitis from swine referred to as principals. Abscesses, mostly in the head and neck, developed in at least a third of all swine in the various groups fed these CTC concentrations. Feeding of 220 mg of CTC/kg of feed in experiment 1 began 12 weeks after exposure of principals to an untypeable group E streptococci (GES; isolate 3X29A). In experiment 2, feeding of 110 and 220 mg of CTC/kg of feed began 5 weeks after exposure of principals to GES and feeding of 440 mg of CTC/kg of feed began 6 weeks after exposure. One or more cohabitating sentinel swine of experiment 1 and one or more sentinels in all groups of principals of experiment 2, except group 2, developed abscesses that were mostly in the head and neck. In experiment 2, correlation between serum GES antibody titer and development of one or more abscesses in the principals was highly significant (P < 0.01); however, correlation between antibody titer and abscesses in the sentinels only approached significance (P < 0.10).

The efficacy of dihydrostreptomycin in stopping the shedding of Leptospira hardjo subtype hardjobovis was studied in naturally infected cows. Blood and urine samples were collected from dairy cows kept on a farm where the farmer had contracted L hardjobovis infection. A microscopic agglutination test and an ELISA were used to determine specific antibody responses in serum. Polymerase chain reaction was used to detect bacterial shedding in urine. On the first sample collection date, 6 cows were seropositive, and 3 of those shed leptospires in the urine. These 3 cows were treated once with 25 mg of dihydrostreptomycin/kg of body weight. Within 1 week, the 3 cows stopped shedding leptospires. Six weeks later, 8 more lactating cows were found to be shedding leptospires. These cows were also treated once with dihydrostreptomycin, and they too stopped shedding leptospires within 1 week. From then on, the whole herd was examined weekly for a period of 2 months, and all cows Leptospira-positive by polymerase chain reaction were treated once with dihydrostreptomycin. Again, all cows stopped shedding leptospires in the urine within 1 week after treatment with dihydrostreptomycin. After a single treatment of the whole herd at the same time, new infections were not seen.