SummaryMacrophages are critical effectors of the early innate response to bacteria in tissues. Phagocytosis and killing of bacteria are interrelated functions essential for bacterial clearance but the rate‐limiting step when macrophages are challenged with large numbers of the major medical pathogen Staphylococcus aureus is unknown. We show that macrophages have a finite capacity for intracellular killing and fail to match sustained phagocytosis with sustained microbial killing when exposed to large inocula of S. aureus (Newman, SH1000 and USA300 strains). S. aureus ingestion by macrophages is associated with a rapid decline in bacterial viability immediately after phagocytosis. However, not all bacteria are killed in the phagolysosome, and we demonstrate reduced acidification of the phagolysosome, associated with failure of phagolysosomal maturation and reduced activation of cathepsin D. This results in accumulation of viable intracellular bacteria in macrophages. We show macrophages fail to engage apoptosis‐associated bacterial killing. Ultittop mately macrophages with viable bacteria undergo cell lysis, and viable bacteria are released and can be internalized by other macrophages. We show that cycles of lysis and reuptake maintain a pool of viable intracellular bacteria over time when killing is overwhelmed and demonstrate intracellular persistence in alveolar macrophages in the lungs in a murine model.

Key points > COVID-19 is associated with a hypercoagulable state with increased VTE rate. > COVID-19 patients frequently have very high von Willebrand factor (vWF) and factor VIIIc levels that are comparable to those seen in ICU patients with severe sepsis. > Further studies are needed urgently to evaluate the use of vWF as a pragmatic measure to stratify thrombotic risk in COVID-19.

Accurate figures allowing a realistic assessment of the athletic future of a foal following treatment for septic arthritis are of significance for both owner and treating veterinarian.

Summary This paperdescribes the use of a latex agglutination assay to measure serum amyloid A (SAA) in the neonatal foal. The normal range and response to clinical disease was determined. This retrospective study evaluated SAA concentrations over the first 3 days postpartum of 226 Thoroughbred foals judged to be clinically healthy. The normal range for each day was determined; levels were found to be significantly highest on Day 2 (Day 1 vs. Day 2 P<0.0001). The 95th percentile for Days 1–3 was 27.1 mg/l. Clinical records of 133 foals, presented as first or second opinion cases, were evaluated. Foals were divided into 4 groups; septicaemia (S), focal infection (FI), failure of passive transfer (FPT) and noninfectious disease (NI). There was a statistically significant difference (P<0.0001) between SAA concentrations of control foals compared to Groups S and FI. There was no statistically significant difference between controls and Groups FPT and NI. When Group NI was compared to Groups S and FI, there was a statistically significant difference (P<0.0001). The authors suggest that SAA determined by this latex agglutination assay might be a helpful aid in the diagnosis of septicaemia and focal infection in neonatal foals; levels >100 mg/l are highly suggestive of infection in young foals.

Summary A survey of 77 normal and 326 diarrhoeic foals in Britain and Ireland from 1987 to 1989 revealed a significantly higher prevalence of Group A rotaviruses and Aeromonas hydrophila in diarrhoeic foals. The prevalence of cryptosporidia, potentially pathogenic Escherichia coli, Yersinia enterocolitica and Clostridium perfringens was similar in normal or diarrhoeic foals. Rotaviruses had a similar prevalence in all age groups of scouring foals up to three months of age, with an overall prevalence of 37 per cent among diarrhoeic foals. The number of cases of diarrhoea varied considerably from year to year, but in all three years of the survey rotavirus was a significant pathogen. A comparison of diagnostic tests for rotavirus in the faeces showed electron microscopy (EM) and polyacrylamide gel electrophoresis (PAGE) to have similar sensitivity. The Rotazyme ELISA test kit was found to have the same sensitivity as a combination of EM and PAGE. A. hydrophila had an overall prevalence of 9 per cent among diarrhoeic foals, although its prevalence was higher in some age groups. A. hydrophila has not been established previously as a significant enteric pathogen in foals. Other putative pathogens found at very low prevalence were coronavirus, the putative picobirnavirus, Campylobacter spp. and Salmonella spp. No evidence was found of synergistic effects between rotavirus, cryptosporidia and potentially pathogenic E. coli. Neither coccidia nor non‐Group A rotaviruses were found in any of the samples examined.