Investigation of Extracted Plasma Cell-Free DNA as a Biomarker in Foals with Sepsis

Cell-free DNA (cfDNA) is fragmented extracellular DNA that is released from cells into various body fluids. Previously published data from adult horses supports cfDNA as a potential disease biomarker, but also shows that direct measurement in plasma is inaccurate due to matrix effect. It is currently unknown whether a similar matrix effect exists in foal plasma. Given this, the objectives of the current study were to investigate foal plasma for potential matrix effect during fluorescence measurement of cfDNA using a Qubit fluorometer, and to determine whether neat and/or extracted plasma cfDNA concentrations are significantly different in healthy, sick non-septic (SNS) or septic foals. We hypothesized that matrix effect would interfere with accurate fluorescent measurement of cfDNA in foal plasma. Further, we hypothesized that mean extracted cfDNA concentrations, and/or extracted cfDNA:neutrophil ratio, would be elevated in plasma of septic foals compared to healthy or SNS foals. Cell-free DNA was measured in neat plasma, and following DNA extraction with a commercial kit, from 60 foals. Foal plasma exhibited both autofluorescence and non-specific dye binding, confirming matrix effect. However, even with extraction, no significant difference was found in cfDNA concentrations, or cfDNA:neutrophil ratios, between healthy (sepsis score ≤ 5), SNS (sepsis score 6-11 and negative blood culture), or septic (sepsis score ≥ 12 ± positive blood culture) foals. Our data show that matrix effect interferes with accurate Qubit measurement of cfDNA in foal plasma and supports previous findings that plasma cfDNA concentrations are not associated with sepsis diagnosis in foals. Further research is needed to better understand neutrophil function and dysfunction in foal sepsis.

Association of the neutrophil-lymphocyte ratio with outcome in sick hospitalized neonatal foals

BACKGROUND

The neutrophil-lymphocyte ratio (NLR) in human medicine is an objective biomarker that reflects prognosis. The NLR as an independent biomarker to help predict nonsurvival in hospitalized neonatal foals has not been thoroughly interrogated.

OBJECTIVES/HYPOTHESIS

Retrospectively evaluate if the NLR at admission is associated with nonsurvival in sick hospitalized foals <4 days old. We hypothesized that a lower NLR will be associated with nonsurvival.

ANIMALS

One thousand one hundred ninety-six client-owned foals <4 days old of any breed and sex: 993 hospitalized foals and 203 healthy foals.

METHODS

Retrospective multicenter study. Medical records of foals presenting to 3 equine referral hospitals were reviewed. Foals were included if they had complete CBCs, sepsis scores, and outcome data. The NLR was calculated by dividing the absolute neutrophil count by the absolute lymphocyte count. Data were analyzed by nonparametric methods and univariate analysis.

RESULTS

Of the 993 sick hospitalized foals, 686 were sick nonseptic and 307 were septic. The median NLR was lower in sick hospitalized foals (median [95% confidence interval], 3.55 [0.5-13.9]) compared with healthy foals (6.61 [3.06-18.1]). Septic foals had the lowest NLR (2.00 [0.20-9.71]). The NLR was lower in nonsurviving (1.97 [1.67-2.45]) compared with surviving foals (4.10 [3.76-4.33]). Nonsurviving septic foals had the lowest NLR (1.47 [1.70-3.01]). Foals with a NLR of <3.06 or <1.6 at admission had odds ratio of 3.21 (2.24-4.29) and 4.03 (2.86-5.67) for nonsurvival, respectively.

CONCLUSIONS AND CLINICAL IMPORTANCE

A NLR < 3.06 at admission in sick hospitalized foals is readily available and clinically useful variable to provide prognostic information.

Assessment of the hypothalamic-pituitary-adrenocortical axis function using a vasopressin stimulation test in neonatal foals

BACKGROUND

Bacterial sepsis is the leading cause of death in foals and is associated with hypothalamic-pituitary-adrenocortical axis (HPAA) dysfunction. HPAA function can be evaluated by an arginine-vasopressin (AVP) stimulation test.

HYPOTHESES/OBJECTIVES

Administration of AVP will stimulate a dose-dependent rise in systemic adrenocorticotropin-releasing hormone (ACTH) and cortisol in neonatal foals. There will be no response seen in corticotropin-releasing hormone (CRH) and baseline AVP will be within reference interval.

ANIMALS

Twelve neonatal foals, <72 hours old.

METHODS

HPAA function was assessed in foals utilizing 3 doses of AVP (2.5, 5, and 7.5 IU), administered between 24 and 48 hours of age in this randomized cross-over study. Cortisol, ACTH, CRH and AVP were measured at 0 (baseline), 15, 30, 60 and 90 minutes after AVP administration with immunoassays. The fold increase in cortisol and ACTH was calculated at 15 and 30 minutes compared to baseline.

RESULTS

All doses of AVP resulted in a significant increase in cortisol concentration over time, and a dose-dependent increase in ACTH concentration over time. ACTH and cortisol were significantly increased at 15 and 30 minutes, respectively after all 3 doses of AVP compared to baseline (P < .01). There was no change in endogenous CRH after stimulation with AVP.

CONCLUSION AND CLINICAL IMPORTANCE

Administration of AVP is safe and results in a significant rise in ACTH and cortisol in neonatal foals. A stimulation test with AVP (5 IU) can be considered for HPAA assessment in septic foals.

The hypothalamic-pituitary-adrenal axis response to ovine corticotropin-releasing-hormone stimulation tests in healthy and hospitalized foals

BACKGROUND

The hypothalamic-pituitary-adrenocortical axis (HPAA) response to sepsis can be impaired in critical illness. Corticotropin-releasing hormone (CRH) stimulation test might assess HPAA function in foals.

OBJECTIVE

To evaluate plasma cortisol, ACTH, arginine vasopressin (AVP), and endogenous CRH (eCRH) response to different doses of ovine CRH (oCRH).

ANIMALS

Healthy (n = 14) and hospitalized (n = 15) foals <7 days of age.

METHODS

In this prospective randomized study, oCRH (0.1, 0.3, and 1 μg/kg) was administered intravenously and blood samples were collected before, 15, 30, 60, and 90 minutes after administration of oCRH to determine plasma hormone concentrations. The hormonal response was evaluated as the difference (Delta; μg/dL or pg/mL) or percent change between baseline hormone concentration and each time point after oCRH stimulation.

RESULTS

Cortisol concentrations increased from baseline at 15 minutes with 0.1 and 0.3 μg/kg and at 30 and 60 minutes from baseline with 1 μg/kg oCRH (P < .05) in healthy and hospitalized foals. ACTH concentrations increased from baseline at 15 minutes with 0.1 μg/kg and at 30 minutes with 1 μg/kg oCRH (P < .05) in hospitalized foals. Delta cortisol 0 - 30, ACTH 0 - 30, and eCRH 0 - 30 was higher for the 1 μg/kg compared with 0.1 μg/kg oCRH in healthy foals (P < .05). Delta ACTH 0 - 15 and eCRH 0 - 30 was higher for the 1 μg/kg compared with the lower doses of oCRH in hospitalized foals (P < .05).

CONCLUSIONS AND CLINICAL IMPORTANCE

Cortisol, ACTH, and eCRH concentrations increased in response to administration of all doses of oCRH. One microgram per kilogram of oCRH appears to be optimal for the assessment of HPAA in healthy and hospitalized foals.

Equine blood cultures: Can we do better?

Blood culture is considered the gold standard test for documenting bacteraemia in patients with suspected bacterial sepsis in veterinary and human medicine. However, blood culture often fails to yield bacterial growth even though the clinical picture is strongly suggestive of bacterial sepsis, or contaminating organisms can overgrow the true pathogen, making accurate diagnosis and appropriate management of this life-threatening condition very challenging. Methodology for collecting blood cultures in equine medicine, and even in human hospitals, is not standardised, and many variables can affect the yield and type of microorganisms cultured. Microbiological culture techniques used in the laboratory and specific sample collection techniques, including volume of blood collected, aseptic technique utilised, and the site, timing and frequency of sample collection, all have substantial impact on the accuracy of blood culture results. In addition, patient-specific factors such as husbandry factors, the anatomical site of the primary infection, and changing microflora in different geographic locations, also can impact blood cultures. Thus, blood cultures obtained in practice may not always accurately define the presence or absence of, or specific organisms causing, bacteraemia in horses and foals with suspected sepsis. Erroneous blood culture results can lead to inappropriate antimicrobial use, which can result in poor outcomes for individual patients and contribute to the development of antimicrobial resistance in the patient's microflora and the environmental microcosm. This review summarises current indications and methodology, and specific factors that may be optimised, for equine blood culture, with particular focus on available literature from neonatal foals with suspected bacterial sepsis. To standardise and optimise blood culture techniques in horses and foals, future research in this area should be aimed at determining the optimal volume of blood that should be collected for culture, and the ideal site, timing, and frequency of sample collection.

The enteroinsular axis during hospitalization in newborn foals

The enteroinsular axis (EIA) is an energy regulatory system that modulates insulin secretion through the release of enteroendocrine factors (incretins). Despite the importance of energy homeostasis in the equine neonate, information on the EIA in hospitalized foals is lacking. The goals of this study were to measure serum insulin and plasma incretin (glucose-dependent insulinotropic polypeptide [GIP], glucagon-like peptide-1 [GLP-1] and glucagon-like peptide-2 [GLP-2]) concentrations, to determine the insulin and incretin association, as well as their link to disease severity and outcome in hospitalized foals. A total of 102 newborn foals ≤72 h old were classified into hospitalized (n = 88) and healthy groups (n = 14). Hospitalized foals included septic (n = 55) and sick non-septic (SNS; n = 33) foals based on sepsis scores. Blood samples were collected over 72 h to measure serum insulin and plasma GIP, GLP-1 and GLP-2 concentrations using immunoassays. Data were analyzed by nonparametric methods and univariate logistic regression. At admission, serum glucose and insulin and plasma GIP were significantly lower in hospitalized and septic compared to healthy foals (P < 0.01), while plasma GLP-1 and GLP-2 concentrations were higher in hospitalized and septic foals than healthy and SNS foals, and decreased over time in septic foals (P < 0.05). As a percent of admission values, GLP-1 and GLP-2 concentrations dropped faster in healthy compared to hospitalized foals. Serum insulin concentrations were lower in hospitalized and septic non-survivors than survivors at admission (P < 0.01). Hospitalized foals with serum insulin < 5.8 µIU/mL, plasma GLP-1 >68.5 pM, and plasma GLP-2 >9 ng/mL within 24 h of admission were more likely to die (OR = 4.2; 95% CI = 1.1-16.1; OR = 13.5, 95% CI = 1.4-123.7; OR = 12.5, 95% CI = 1.6-97.6, respectively; P < 0.05). Low GIP together with increased GLP-1 and GLP-2 concentrations indicates that different mechanisms may be contributing to reduced insulin secretion in critically ill foals, including impaired intestinal production (GIP, proximal intestine) and pancreatic endocrine resistance to enhanced incretin secretion (GLP-1, GLP-2; distal intestine). These imbalances could contribute to energy dysregulation in the critically ill equine neonate.

Emergency Management of Equid Foals in the Field

Foal emergencies can be intimidating to manage in the field, yet many conditions will respond well to the supportive care possible on the farm. Triage of the foal targets focused supportive care to stabilize the foal before referral to a hospital or to facilitate the management in the field. There are many diagnostic and therapeutic options available in the field setting to support a successful outcome on the farm.

Utility of cell-free DNA concentrations and illness severity scores to predict survival in critically ill neonatal foals

Plasma cell-free DNA (cfDNA) levels have been associated with disease and survival status in septic humans and dogs. To date, studies investigating cfDNA levels in association with critical illness in foals are lacking. We hypothesized that cfDNA would be detectable in the plasma of foals, that septic and sick-nonseptic foals would have significantly higher cfDNA levels compared to healthy foals, and that increased cfDNA levels would be associated with non-survival. Animals used include 80 foals of 10 days of age or less admitted to a tertiary referral center between January and July, 2020 were stratified into three categories: healthy (n = 34), sick non-septic (n = 11) and septic (n = 35) based on specific criteria. This was a prospective clinical study. Blood was collected from critically ill foals at admission or born in hospital for cfDNA quantification and blood culture. Previously published sepsis score (SS) and neonatal SIRS score (NSIRS) were also calculated. SS, NSIRS, blood culture status and cfDNA concentrations were evaluated to predict survival. Continuous variables between groups were compared using Kruskal-Wallis ANOVA with Dunn’s post hoc test. Comparisons between two groups were assessed using the Mann-Whitney U-test or Spearman rank for correlations. The performance of cfDNA, sepsis score and NSIRS score to predict survival was assessed by receiver operator characteristic (ROC) curve analysis including area under the curve, sensitivity and specificity using cutoffs. Plasma cfDNA was detectable in all foals. No significant differences in cfDNA concentration were detected between healthy foals and septic foals (P = 0.65) or healthy foals and sick non-septic foals (P = 0.88). There was no significant association between cfDNA and culture status, SS, NSIRS or foal survival. SS (AUC 0.85) and NSIRS (AUC 0.83) were superior to cfDNA (AUC 0.64) in predicting survival. Although cfDNA was detectable in foal plasma, it offers negligible utility to diagnose sepsis or predict survival in critical illness in neonates.

Factors associated with the risk of positive blood culture in neonatal foals presented to a referral center (2000-2014)

Background

Bloodstream infections (BSI) are common in sick foals and increase foal morbidity and mortality when they occur. Recognition of risk factors for BSI could be an important means to limit their occurrence, but studies on this topic are limited.

Objectives

Historical as well as maternal and foal physical examination findings will predict risk of BSI in neonatal foals.

Animals

Foals <14 days of age admitted to a referral equine hospital for care.

Methods

Retrospective case‐control study with univariate and multivariable logistic regression analysis.

Results

Four hundred twenty‐nine (143 cases and 286 controls) foals <14 days of age were studied. Risk of a foal having a BSI was increased in foals with umbilical disease (adjusted odds ratio [OR], 11.01; P = .02), hypoglycemia (adjusted OR, 13.51; P = .03), and the combined presence of umbilical disease and low hematocrit (adjusted OR, >999.99; P = .04). Factors not found to be risk factors for development of BSI included prematurity, hypothermia, abdominal disease, diarrhea, failure of passive transfer, and maternal uterine infection.

Conclusions and Clinical Importance

Several historical and physical examination findings increase the risk of foals being blood culture positive at presentation to the hospital. This knowledge may aid early identification of blood culture status, thus aiding in treatment decisions.

Septic Arthritis/Osteomyelitis May Lead to Osteochondrosis-Like Lesions in Foals

Failure of the cartilage canal blood supply leads to ischemic chondronecrosis which causes osteochondrosis, and osteochondral lesions. Osteochondrosis is a disease with a heritable component and usually occurs under aseptic conditions. Because bacteria can bind to growth cartilage and disrupt the blood supply in pigs and chickens, we considered whether this might play a role in development of equine osteochondrosis. The aim of this study was to examine whether bacteria are present in canals in the growth cartilage of foals with septic arthritis/osteomyelitis, and whether this is associated with osteochondrosis. The material consisted of 7 foals aged 9-117 days euthanized because of septic arthritis/osteomyelitis. The 7 cases had 16 lesions in growth cartilage that were evaluated histologically. Bacteria were present in cartilage canals in foals with septic arthritis/osteomyelitis. Portions of necrotic canals adjacent to bacteria frequently contained neutrophils, termed acute septic canals; or granulation tissue with neutrophils, termed chronic septic canals. Acute and chronic septic canals were associated with ischemic chondronecrosis in the articular-epiphyseal cartilage complex (AECC) of 5 cases and in the physis of 2 cases, and ossification was focally delayed in 5 of those 7 cases. Lesions occurred with and without adjacent osteomyelitis. Bacteria were present in cartilage canals and were associated with focal chondronecrosis in both the AECC and the physis. This establishes sepsis as a plausible cause of some osteochondral lesions in horses. It is recommended that horses with sepsis-related osteochondral lesions may be used for breeding without increasing the prevalence of OCD-predisposing genes in the population.

Evaluation of updated sepsis scoring systems and systemic inflammatory response syndrome criteria and their association with sepsis in equine neonates

Background

The original equine sepsis score provided a method of identifying foals with sepsis. New variables associated with sepsis have been evaluated, but the sepsis score has not been updated.

Objectives

To evaluate the sensitivity and specificity of 2 updated sepsis scores and the systemic inflammatory response syndrome (SIRS) criteria in regard to detecting sepsis in foals.

Animals

Two‐hundred and seventy‐three ill foals and 25 healthy control foals.

Methods

Historical, physical examination, and clinicopathologic findings were used to calculate the original sepsis score and 2 updated sepsis scores. SIRS criteria were also evaluated. Sepsis scores and positive SIRS scores were statistically compared to foals with sepsis.

Results

One‐hundred and twenty‐six foals were septic and 147 sick‐nonseptic. The original and updated sepsis scores were significantly higher in septic foals as compared to sick‐nonseptic and healthy foals. The sensitivity and specificity of the updated sepsis scores to predict sepsis were not significantly better than those of the original sepsis score. One‐hundred and twenty‐seven of 273 (46.5%) foals met the original SIRS criteria and 88/273 (32%) foals met the equine neonatal SIRS criteria. The original SIRS criteria had similar sensitivity and specificity for predicting sepsis as did the 3 sepsis scores in our study.

Conclusions and Clinical Importance

The updated sepsis scores did not provide improved ability in predicting sepsis. Fulfilling the original SIRS criteria provided similar sensitivity and specificity in predicting sepsis as the modified sepsis score and might serve as a diagnostic aid in identifying foals at risk for sepsis.

Factors associated with outcome and gradual improvement in survival over time in 1065 equine neonates admitted to an intensive care unit

REASONS FOR PERFORMING STUDY

There is a paucity of information regarding the association between common disorders and outcome over time in a large population of ill equine neonates.

OBJECTIVES

To describe the relative frequency of neonatal disorders in a large population of foals admitted to a neonatal intensive care unit, to determine the disorders and factors associated with nonsurvival and determine if the outcome of ill neonatal foals has improved over time.

STUDY DESIGN

Retrospective study.

METHODS

Cases were selected from equine neonatal (≤14 days of age) admissions between 1982 and 2008. Multivariable logistic regression was used to identify the disorders, clinical parameters and laboratory variables associated with nonsurvival or natural death and assess survival over time after accounting for potential confounding variables.

RESULTS

A total of 1065 foals were included in the study. Overall, 775 of 1065 (72.8%) foals survived to be discharged from the hospital and 290 (27.2%) foals were nonsurvivors. Age at admission, sepsis score, proportion of foals with positive blood cultures and proportion of survivors were significantly different (P<0.001) between primary disease categories. Variables retained in the multivariable model for nonsurvival included positive blood culture, neutrophils <2.28 × 10⁹ /l, temperature ≤37.6°C, bicarbonate, PCO₂ , presence of infectious orthopaedic disorders and sepsis score. The adjusted odds of survival for foals admitted in the 2000s were approximately 3.4 (95% CI = 1.9-6.0, P<0.001) times higher than that of foals admitted in the 1980s.

CONCLUSIONS

Primary disorders, sepsis, temperature, acid base status and neutropenia are the main factors that affect outcome in this population of equine neonates. The survival of foals admitted to a neonatal intensive care unit has increased dramatically over a 26 year period.

Plasma C-reactive protein and haptoglobin concentrations in critically ill neonatal foals

Background

Accurate diagnostic markers for sepsis in neonatal foals are needed. Plasma C‐reactive protein concentration (p[CRP]) and haptoglobin concentration (p[Hp]) are well‐established biomarkers of infection in humans, but studies are lacking in foals.

Hypotheses

p[CRP]) and p[Hp] are increased in septic foals compared to sick nonseptic and healthy control foals, and are predictive of survival.

Animals

Eighty critically ill foals (40 septic, 40 sick nonseptic) and 39 healthy control foals <1 week of age.

Methods

Multicenter, prospective observational clinical study. Venous blood was collected at admission from septic and sick nonseptic foals and from clinically healthy foals at 24 h of age. A diagnosis of sepsis was made based on positive blood culture or a sepsis score >11, and p[CRP] and p[Hp] were measured by using ELISA tests. Data were analyzed by using the Mann‐Whitney U‐test and forward stepwise multivariable linear regression. P < .05 was considered significant.

Results

Plasma [CRP] was positively associated with age, serum globulin, adrenomedullin, and bilirubin concentrations, aspartate aminotransferase activity, glutamyl‐transferase activity, band neutrophil count, and rectal temperature, and was increased in foals with toxic neutrophils, enterocolitis, colic, rib fractures and septic arthritis. Surprisingly, p[Hp] was lower in septic foals than in sick nonseptic foals. Neither p[CRP] or p[Hp] was predictive of survival in critically ill foals.

Conclusions and Clinical Importance

Plasma [CRP] increases with inflammation in neonatal foals but is not indicative of sepsis. Single time point, admission sampling of p[CRP] and p[Hp] do not appear to be useful biomarkers for sepsis in foals.