Severe Hyperthermia Research Articles

Motor performance is preserved in healthy aged adults following severe whole-body hyperthermia

Healthy aging is associated with a progressive decline in motor performance and thermoregulatory efficiency. Functional consequences of severe whole-body hyperthermia on neurophysiological functions in healthy aged men have not been investigated. To determine whether severe whole-body hyperthermia (increase in rectal temperature of about 2.5 °C) induced by lower-body heating in older men (64–80 years, n = 9) would suppress excitability of reflexes, voluntarily and electrically induced ankle plantar flexor contractile properties were compared with those in young men (19–21 years, n = 11). Though no aging effect on hyperthermia-induced reflex amplitudes was observed, a decrease in maximal H-reflex and V-wave latencies was found to be greater in older than in young men. In older men, lower-body heating was accompanied by a significant increase in twitch and tetani test torque in parallel with a greater decrease in muscle contraction time. There was no temperature-depended aging effect on the voluntary activation and maximal voluntary torque production. Despite delayed and weakened thermoregulation and age-related decline in neuromuscular function, motor performance in whole-body severe hyperthermia is apparently preserved in healthy aging.

Does Gender Affect Rectal Temperature Cooling Rates? A Critically Appraised Topic.

Clinical Scenario: Exertional heat stroke (EHS) is a medical emergency characterized by body core temperatures >40.5°C and central nervous system dysfunction. An EHS diagnosis should be immediately followed by cold-water immersion (CWI). Ideally, EHS victims cool at a rate >0.15°C/min until their temperature reaches 38.9°C. While generally accepted, these EHS treatment recommendations often stem from research that examined only males. Since gender differences exist in anthropomorphics (eg,body surface area, lean body mass) and anthropomorphics impact CWI cooling rates, it is possible that CWI cooling rates may differ between genders. Clinical Question: Do CWI rectal temperature (Trec) cooling rates differ between hyperthermic males and females? Summary of Findings: The average Trec cooling rate across all examined studies for males and females was 0.18 (0.05) and 0.24 (0.03)°C/min, respectively. Hyperthermic females cooled ∼33% faster than males. Clinical Bottom Line: Hyperthermic females cooled faster than males, most likely because of higher body surface area to mass ratios and less lean body mass. Regardless of gender, CWI is highly effective at lowering Trec. Clinicians must be able to treat all EHS victims, regardless of gender, with CWI, given its high survival rate when implemented appropriately. Strength of Recommendation: Moderate evidence (2 level 3 studies) suggests that females cool faster than males when treated with CWI following severe hyperthermia. Despite gender differences, cooling rates exceeded cooling rate recommendations for EHS victims (ie,0.15°C/min).

Proteomic identification of hippocalcin and its protective role in heatstroke-induced hypothalamic injury in mice.

Heatstroke is a devastating condition that is characterized by severe hyperthermia and central nervous system dysfunction. However, the mechanism of thermoregulatory center dysfunction of the hypothalamus in heatstroke is unclear. In this study, we established a heatstroke mouse model and a heat-stressed neuronal cellular model on the pheochromocytoma-12 (PC12) cell line. These models revealed that HS promoted obvious neuronal injury in the hypothalamus, with high pathological scores. In addition, PC12 cell apoptosis was evident by decreased cell viability, increased caspase-3 activity, and high apoptosis rates. Furthermore, 14 differentially expressed proteins in the hypothalamus were analyzed by fluorescence two-dimensional difference gel electrophoresis and identified by matrix-assisted laser desorption ionization time-of-flight mass spectrometry. Expression changes in hippocalcin (HPAC), a downregulated neuron-specific calcium-binding protein, were confirmed in the hypothalamus of the heatstroke mice and heat-stressed PC12 cells by immunochemistry and western blot. Moreover, HPAC overexpression and HPAC-targeted small interfering RNA experiments revealed that HPAC functioned as an antiapoptotic protein in heat-stressed PC12 cells and hypothalamic injury. Lastly, ulinastatin (UTI), a cell-protective drug that is clinically used to treat patients with heatstroke, was used in vitro and in vivo to confirm the role of HPAC; UTI inhibited heat stress (HS)-induced downregulation of HPAC expression, protected hypothalamic neurons and PC12 cells from HS-induced apoptosis and increased heat tolerance in the heatstroke animals. In summary, our study has uncovered and demonstrated the protective role of HPAC in heatstroke-induced hypothalamic injury in mice.

Liver Transplantation for Fulminant Hepatic Failure Due to Heat Stroke: A Case Report

Heat stroke is a condition caused by an excessive increase in body temperature in a relatively short period of time, and is clinically characterized by central nervous system dysfunction, including delirium, seizures, coma, and severe hyperthermia. In this context, the resulting fulminant hepatic failure makes liver transplant the best choice when there are no guarantees of better results with conservative treatment. We present our experience in this case, possible alternative choices, and the current role of liver transplantation in the resolution of fulminant liver failure due to heat stroke. Case ReportWe report the case of a 32-year-old man with a history of malabsorption syndrome and unconfirmed celiac disease controlled with a gluten-free diet, who, while working on a typical summer midday in southern Spain (approximately 40°C), abruptly presented with loss of consciousness, coma, and a temperature of 42°C, as well as seizures at the initial medical assessment that subsided after the administration of diazepam. On the third day, the patient presented with multiple organ dysfunction syndrome, requiring mechanical ventilation, hemodialysis, and inotropic support. He did not improve with the support of conservative treatment, therefore it was decided to perform an urgent liver transplant, after which he recovered completely. ConclusionsLiver transplantation should be a main choice of treatment for cases in which, despite intensive medical treatment, there is still clinical and analytical evidence of massive and/or irreversible hepatocellular damage.

Warming the premature infant in the delivery room: Quantification of the risk of hyperthermia

AimThe efficacy and safety of three polyethylene bags commonly used to prevent hypothermia in premature infants was assessed. MethodsTo simulate transfer from the delivery room to a secondary care unit, a thermally stable, bonneted mannequin (skin temperature: 34.4 °C) was placed in a climate chamber under different conditions: with a radiant warmer, with various polyethylene bags (open on one side, closed by a draw-string at the neck, or a “life support pouch” with several access points) or without a bag. ResultsWith the radiant warmer turned on, the mean reduction in heat loss from the nude mannequin was 50.8 ± 1.7% (p < 0.0001, vs. warmer off). The mean reduction in heat loss (vs. no bag) was 55.0 ± 0.9% for the drawstring bag, 49.0 ± 2.2% for the standard bag (p = 0.0001), and 48.1 ± 0.7% for the life support pouch (p = 0.006). When a radiant warmer + polyethylene bag were used, heat stress (body temperature: 38 °C) and severe hyperthermia (40 °C) occurred after 11 and 34 min, respectively. ConclusionCaution must be taken when using a radiant warmer and polyethylene bag with a premature infant. Heat stress can occur in only 11 min. Continuous body temperature monitoring is therefore required.

Does Precooling With Whole-Body Immersion Affect Thermal Sensation or Perceived Exertion? A Critically Appraised Topic.

Clinical Scenario: Exertional heat stroke (EHS) is a potentially deadly heat illness and poses a significant health risk to athletes; EHS survival rates are near 100% if properly recognized and treated. Whole-body cold water immersion (CWI) is the most effective method for lowering body core temperature. Precooling (PC) with CWI before exercise may prevent severe hyperthermia or EHS by increasing the body's overall heat storage capacity. However, PC may also alter athletes' perception of how hot they feel or how hard they are exercising. Consequently, they may be unable to accurately perceive their body core temperature or how hard they are working, which may predispose them to severe hyperthermia or EHS. Clinical Question: Does PC with whole-body CWI affect thermal sensation (TS) or rating of perceived exertion (RPE) during exercise in the heat? Summary of Key Findings: In 4 studies, RPE during exercise ranged from 12 (2.0) to 20 (3.0), with no clinically meaningful differences between PC and control trials. TS scores ranged from 2 (1.0) to 8 (0.5) in control trials and from 2 (1.0) to 7.5 (0.5) during PC trials. Clinical Bottom Line: PC did not cause clinically meaningful differences in RPE or TS during exercise. It is unlikely that PC would predispose athletes to EHS by altering perceptions of exercise intensity or body core temperature. Strength of Recommendation: None of the reviewed studies (all level-2 studies with Physiotherapy Evidence Database scores ≥ 5) suggest that PC with CWI influences RPE or TS in exercising males.

Glucocorticoid receptor activation is associated with increased resistance to heat‐induced hyperthermia and injury

Anti-inflammatory mediators likely play a key role in maintaining thermal homeostasis and providing protection against heat stress. The aim of this study was to investigate the association between activation of the glucocorticoid receptor (GR) and resistance to heat-induced hyperthermia and injury. Effects of heat exposure on core body temperature, muscle GR phosphorylation status and subcellular expression were examined in control mice and thermal acclimation (TA)-exposed mice. In addition, effects of TA and corticosterone on C2C12 mouse myoblast viability and subcellular GR were assessed during heat exposure. Phosphorylated, nuclear and mitochondrial GR levels were significantly higher in the gastrocnemius muscles of mice with mild hyperthermia (tolerant), compared to mice with severe hyperthermia (intolerant) during a heat exposure test. Similar changes were found in mice after TA, compared to non-TA-exposed controls. Additional groups of TA and non-TA-exposed mice underwent a heat exposure test. TA mice presented a significantly lower hyperthermic response during heat exposure than non-TA-exposed control. C2C12 cells exposed to TA incubation had higher viability against heat shock and showed higher GR levels in their mitochondria and nuclei detected by Western blot analysis and fluorescence microscopy, compared to cells exposed to normal incubation. Furthermore, pre-incubation with 0.1 μM corticosterone increased C2C12 cell viability during heat exposure and mitochondrial and nuclear GR expression. The results of these in vivo and in vitro studies suggest that GR activation is associated with increased resistance against heat-induced hyperthermia and injury.

95 Safety and Efficacy of Dantrolene Sodium (250 mg/5 mL) in Patients With Exertional Heat Stroke

Exertional heat stroke (EHS) is a rare, life-threatening condition that may affect anyone performing intense physical activity, especially in a hot environment. Morbidity and mortality persist despite aggressive cooling. EHS is a leading cause of death in young athletes and non-combat-related deaths in the military. EHS affects outdoor workers, firefighters, and people performing intense physical activities in hot weather. Severe hyperthermia and CNS dysfunction are hallmark features; rhabdomyolysis, renal failure, liver damage, and coagulation abnormalities are common and as many as 1/3 of survivors have long-term neurologic deficits despite the use of aggressive cooling. The study objectives were to evaluate the safety and efficacy of dantrolene sodium 250 mg/5 mL (DS) for injectable suspension for the treatment of EHS, administered as an adjunct to standard body cooling (SBC). This was a randomized, 2-arm, parallel, open-label study evaluating DS plus SBC compared to SBC alone in patients with EHS. EHS was defined as a core body temperature ≥40.0°C, impaired level of consciousness (LOC)(Glasgow Coma Scale, GCS score <13), and tachycardia. SBC was defined as efficient body cooling plus supportive measures. Patients were randomized 1:1 (n=17 per group). The primary endpoint was the cumulative incidence of recovery of LOC defined as a GCS score ≥13 at ≤90 minutes postrandomization. Secondary efficacy endpoints included calculated cooling rates and rectal temperature values. Safety and tolerability were assessed. The modified intent-to-treat (mITT) population excluded patients with endotracheal intubation at baseline, which made full assessment of GCS unfeasible. The study was conducted in a real-world emergency medicine setting. Due to the rareness and unpredictable nature of EHS, the study was designed to evaluate clinically meaningful outcomes and not powered for statistical significance. Demographics and baseline characteristics were balanced between the treatment groups. A total of 61.8% of patients were male. Mean age was 40.7 years (range 18-45). Mean baseline rectal temperature was 41.4°C; mean baseline GCS score was 6. Ten patients required rapid sequence intubation on presentation. More patients in the DS plus SBC group met the primary endpoint vs SBC alone (29.4% [CI: 10.31, 55.96] vs 11.8% [CI: 1.46, 36.44]). Patients in the DS plus SBC arm cooled faster. The median time to first rectal temperature ≤ 38°C in ≥75% of subjects in the mITT population was 125 min for the DS group vs 195 min for SBC alone. Safety and tolerability findings were similar in both groups. No treatment-emergent adverse events were reported as treatment related or led to discontinuation in either group. SAEs were reported for 11.8% of patients in each group. Seven patients (20.6%) experienced at least 1 SAE, with similar proportions across the 2 groups (DS plus SBC: 23.5%; SBC alone: 17.6%). This well-conducted, randomized, controlled clinical trial demonstrated that DS is safe and well tolerated in subjects with EHS and is consistent with the known, well-characterized safety profile in currently approved indications. DS in addition to SBC demonstrated greater clinically meaningful improvement in neurologic function vs SBC alone. Patients treated with DS in the ITT population were 3 times more likely to achieve recovery in their LOC; whereas, the mITT population were 6 times more likely to achieve recovery.

The incidence of hyperthermia during cochlear implant surgery in children.

Inadvertent hyperthermia during anaesthesia is a rare but life-threatening complication. We have encountered several cases of severe hyperthermia in paediatric patients undergoing anaesthesia for cochlear implantation. This study aimed to describe the clinical characteristics of children who developed hyperthermia while undergoing cochlear implantation, and to explore possible mechanisms and predisposing factors. The anaesthetic charts of all patients aged under 18 years who underwent cochlear implantation, or mastoid or ophthalmic surgery, between 1 January 2006 and 31 December 2009, at Soroka Medical Center in Beer Sheva, Israel, were reviewed. Patients undergoing mastoid and ophthalmic surgical procedures were used as controls. A larger percentage of patients who underwent cochlear implant surgery (10 per cent) developed hyperthermia compared to controls (0.7 per cent, p < 0.05). In five of the seven cases, hyperthermia appeared in combination with tachycardia and hypercapnia, adhering to the clinical triad of malignant hyperthermia. Patients undergoing cochlear implantation are susceptible to developing intra-operative hyperthermia. This article describes the hyperthermic events that occur during paediatric cochlear implantation, and attempts to identify potential triggers of hyperthermia.

Temperate-Water Immersion as a Treatment for Hyperthermic Humans Wearing American Football Uniforms.

Cold-water immersion (CWI; 10°C) can effectively reduce body core temperature even if a hyperthermic human is wearing a full American football uniform (PADS) during treatment. Temperate-water immersion (TWI; 21°C) may be an effective alternative to CWI if resources for the latter (eg, ice) are unavailable. To measure rectal temperature (Trec) cooling rates, thermal sensation, and Environmental Symptoms Questionnaire (ESQ) scores of participants wearing PADS or shorts, undergarments, and socks (NOpads) before, during, and after TWI. Crossover study. Laboratory. Thirteen physically active, unacclimatized men (age = 22 ± 2 years, height = 182.3 ± 5.2 cm, mass = 82.5 ± 13.4 kg, body fat = 10% ± 4%, body surface area = 2.04 ± 0.16 m2). Participants exercised in the heat (40°C, 50% relative humidity) on 2 days while wearing PADS until Trec reached 39.5°C. Participants then underwent TWI while wearing either NOpads or PADS until Trec reached 38°C. Thermal sensation and ESQ responses were collected at various times before and after exercise. Temperate-water immersion duration (minutes), Trec cooling rates (°C/min), thermal sensation, and ESQ scores. Participants had similar exercise times (NOpads = 38.1 ± 8.1 minutes, PADS = 38.1 ± 8.5 minutes), hypohydration levels (NOpads = 1.1% ± 0.2%, PADS = 1.2% ± 0.2%), and thermal sensation ratings (NOpads = 7.1 ± 0.4, PADS = 7.3 ± 0.4) before TWI. Rectal temperature cooling rates were similar between conditions (NOpads = 0.12°C/min ± 0.05°C/min, PADS = 0.13°C/min ± 0.05°C/min; t12 = 0.82, P = .79). Thermal sensation and ESQ scores were unremarkable between conditions over time. Temperate-water immersion produced acceptable (ie, >0.08°C/min), though not ideal, cooling rates regardless of whether PADS or NOpads were worn. If a football uniform is difficult to remove or the patient is noncompliant, clinicians should begin water-immersion treatment with the athlete fully equipped. Clinicians should strive to use CWI to treat severe hyperthermia, but when CWI is not feasible, TWI should be the next treatment option because its cooling rate was higher than the rates of other common modalities (eg, ice packs, fanning).

Abstract A47: Immunogenic cancer cell death induced by high hydrostatic pressure and hyperthermia: Calreticulin exposure pathway

Abstract Immunogenic cell death (ICD) is a type of cell death induced by various chemotherapeutics, physical modalities such as photodynamic therapy, radiotherapy, severe hyperthermia (sHT) or high hydrostatic pressure (HHP). HHP and sHT are able to trigger a specific antitumor immune response and induce the rapid translocation of calreticulin (CRT) to the plasma membrane surface (ecto-CRT). Ecto-CRT on dying tumor cells represents an “eat me” signal for dendritic cells as well as a major molecular determinant that makes the difference between immunogenic and non-immunogenic cell death. Nevertheless, the mechanisms implicated in CRT translocation after HHP treatment is unknown. Inducers of ICD trigger the ER stress response, Reactive Oxygen Species (ROS) generation and Ca2+ release. Kinetics of ecto-CRT was assessed in lung A549 and ovarian OV90 tumor cell lines. CRT localization in sHT- and HHP-treated tumor cells was tracked by endosomal staining (caveolin, clathrin, early and late endosomes) and visualized by confocal microscopy. For detection of CRT translocation pathway, the tumor cells were pretreated with selected cytoskeletal inhibitors, inhibitor of intracellular transport, ER stress activator or small interfering RNA followed by sHT and HHP treatment. The cells were analyzed by flow cytometry and confocal microscopy. Plasma membrane fraction and endosomes were isolated and analyzed by western blotting. Our results indicate that the ROS - PERK - eIF2α - caspase 2 - caspase 8 - caspase 8-mediated cleavage of the ER protein BAP31 is central for the perception of HHP-driven cell death as immunogenic. On the other hand our first results indicate that none of these processes are involve in exposure of CRT on cell surface in sHT treated tumor cells. We observed that sHT treatment does not lead to caspase 8 activation and Bap31 cleavage. However, we showed that translocation of CRT to the cell surface is dependent on endoplasmic reticulum-sessile kinase PERK and presence of Bax/Bak proteins. CRT colocalization with clathrin in tumor cells after HHP and particularly with early endosomes was detected. Surprisingly, we also did not observe colocalization with any endosomes in sHT treated tumor cells. Further, inhibition of microtubule-dependent transport with Nocodazole D results in decrease of CRT transport on cell surface in HHP treated tumor cells. Similar but less significant effect was seen when Brefeldin A was used to inhibit anterograde transport in both treatments. Inhibition of actin polymerization by Cytochalasin D did not significantly affect CRT translocation. In conclusion, PERK seems to play a central role in the exposure of CRT upon induction of ICD. However, up-stream and downstream signaling cascades differ depending the modality used to induce ICD, such as HHP or sHT. Citation Format: Sarka Vosahlikova, Irena Adkins, Linda Urbanova, Nada Hradilova, Lenka Sadilkova, Radek Spisek, Irena Moserova. Immunogenic cancer cell death induced by high hydrostatic pressure and hyperthermia: Calreticulin exposure pathway. [abstract]. In: Proceedings of the AACR Special Conference on Translational Control of Cancer: A New Frontier in Cancer Biology and Therapy; 2016 Oct 27-30; San Francisco, CA. Philadelphia (PA): AACR; Cancer Res 2017;77(6 Suppl):Abstract nr A47.

Successful early application of extracorporeal membrane oxygenation to support cardiopulmonary resuscitation for a patient suffering from severe malignant hyperthermia and cardiac arrest: a case report.

Malignant hyperthermia (MH) may lead to metabolic crisis of skeletal muscle in susceptible individuals following exposure to triggering agents such as volatile anesthetics or depolarizing muscle relaxants. MH is a rare and a potentially lethal disease, which can lead to cardiac arrest. We report a case of severe MH, in which the rapidly evolving signs of hypermetabolism eventually resulted in cardiac arrest. Despite conventional treatments following cardiopulmonary resuscitation, the patient's vital signs did not improve. Therefore, we applied extracorporeal membrane oxygenation for providing hemodynamic support.

Survival Despite Severe Hyperthermia and Multi-Organ System Dysfunction Following Week-Long Use of an MDPV Containing "Stain Remover"

Synthetic amphetamine and cathinone analogs are sympathomimetic hallucinogens that can cause significant toxicity. Hyperthermia in the setting of sympathomimetic overdose is typically associated with a high mortality. We report a case of neurologically intact survival after extreme hyperthermia in the setting of a sympathomimetic overdose. A 29 year-old male ingested a methylenedioxypyrovalerone "stain remover" and exhibited excited delirium and severe sympathomimetic effects. Multi-organ system toxicity included severe hyperthermia, acidosis, hypoglycemia, intracranial hemorrhage, status epilepticus, myocardial infarction, hypotension, rhabdomyolysis, acute renal failure, acute hepatic injury, and coagulopathy. With aggressive cooling, intravenous fluids, benzodiazepine use, peripheral vasopressors, and hemodialysis, he had a good neurologic outcome at the time of discharge after a 17-day hospital course. Despite a high mortality rate with severe hyperthermia, this case suggests that patients with toxin-induced multi-system organ dysfunctionand associated hyperthermia may recover with early aggressive supportive care.

Hyperthermia and supraspinal fatigue.

Hyperthermia and supraspinal fatigue.

In vitro assessment of the effects of temperature on phagocytosis, reactive oxygen species production and apoptosis in bovine polymorphonuclear cells

Heat stress exerts a direct negative effect on farm animal health, triggering physiological responses. Environmental high temperature induces immunosuppression in dairy cows, increasing the risk of mastitis and milk somatic cell counts. The influence of heat stress on leukocytes activities has not been fully elucidated. The present in vitro study was aimed at assessing whether the exposure to temperature simulating conditions of severe whole body hyperthermia affects defensive functions of bovine blood polymorphonuclear cells.Blood was collected from seven clinically healthy, multiparous, late lactating Holstein cows. After isolation, PMN were incubated at either 39 or 41°C. Phagocytosis, respiratory burst and apoptosis were then investigated. The selected temperatures of 39°C or 41°C mimicked conditions of normothermia or severe heat stress, respectively. Phagocytosis assay was carried out by measuring the fluorescence of phagocyted fluorescein-labelled E. coli bioparticles. The modulation of oxidative burst activity was studied by the cytochrome C reduction method. Apoptosis was determined by measuring the activities of two enzymes that play an effector role in the process, namely Caspase-3 and Caspase-7. Statistical analyses were performed using SPSS 22.0. A Student t-test for paired samples and a Generalised Estimating Equation were used based on data distribution.The phagocytosis rate was reduced (−37%, P<0.01) when PMN were incubated for 2h at 41°C, when compared to phagocytosis rate measured at 39°C. The oxidative burst, as determined by extracellular production of reactive oxygen species (ROS), was also reduced by the exposure of cells to 41°C compared to 39°C. Such reduction ranged between −2 and −21% (P<0.05). Apoptosis rate was not affected by different temperatures.The results reported in this study suggest that phagocytosis and ROS production in PMN exposed to severe high temperature are impaired, partially explaining the higher occurrence of infections during periods of hot weather.

Liver Transplantation after Exertional Heatstroke-Induced Acute Liver Failure

Exertional heatstroke (EHS) is a life-threatening disease characterized clinically by central nervous system dysfunction and severe hyperthermia. It frequently occurs among athletes, soldiers, and laborers. While cardiopulmonary symptoms are common in patients undergoing EHS, irreversible acute liver failure is a rarely described phenomenon. When managing cases of EHS complicated by acute liver failure, it is crucial to act promptly with aggressive total body cooling in order to prevent progression of the clinical syndrome. However, an urgent liver transplantation can be a therapeutic strategy when patients fail to improve with supportive measures.

Expert consensus on standardized diagnosis and treatment for heat stroke.

Heat stroke is a life-threatening disease characterized clinically by central nervous system dysfunction and severe hyperthermia (core temperature rises to higher than 40 °C). The unchecked rise of body core temperature overwhelms intrinsic or extrinsic heat generation mechanism, thus overwhelms homoeostatic thermoregulation. Hyperthermia causes cellular and organ dysfunction with progressive exacerbation resulting in multi-organ failure and death. Rapid cooling to reduce core temperatureas quickly as possible is the primary and most effective treatment, as it has been shown that the major determinant of outcome in heatstroke is the degree and duration of hyperthermia. If suppression of body temperature is delayed, the fatality rate will be elevated. This is a guideline for the management of heat stroke, developed by the People’s Liberation Army Professional Committee of Critical Care Medicine lauched in June 2006. This is the first and origianl guideline for heat stroke in Chinese army and is expected to be properly used in daily clinial practice.

Seasonal and geographical variation in heat tolerance and evaporative cooling capacity in a passerine bird.

Intraspecific variation in avian thermoregulatory responses to heat stress has received little attention, despite increasing evidence that endothermic animals show considerable physiological variation among populations. We investigated seasonal (summer versus winter) variation in heat tolerance and evaporative cooling in an Afrotropical ploceid passerine, the white-browed sparrow-weaver (Plocepasser mahali; ∼ 47 g) at three sites along a climatic gradient with more than 10 °C variation in mid-summer maximum air temperature (Ta). We measured resting metabolic rate (RMR) and total evaporative water loss (TEWL) using open flow-through respirometry, and core body temperature (Tb) using passive integrated transponder tags. Sparrow-weavers were exposed to a ramped profile of progressively higher Ta between 30 and 52 °C to elicit maximum evaporative cooling capacity (N=10 per site per season); the maximum Ta birds tolerated before the onset of severe hyperthermia (Tb ≈ 44 °C) was considered to be their hyperthermia threshold Ta (Ta,HT). Our data reveal significant seasonal acclimatisation of heat tolerance, with a desert population of sparrow-weavers reaching significantly higher Ta in summer (49.5 ± 1.4 °C, i.e. higher Ta,HT) than in winter (46.8 ± 0.9 °C), reflecting enhanced evaporative cooling during summer. Moreover, desert sparrow-weavers had significantly higher heat tolerance and evaporative cooling capacity during summer compared with populations from more mesic sites (Ta,HT=47.3 ± 1.5 and 47.6 ± 1.3 °C). A better understanding of the contributions of local adaptation versus phenotypic plasticity to intraspecific variation in avian heat tolerance and evaporative cooling capacity is needed for modelling species' responses to changing climates.

Virulent Properties of Russian Bovine Viral Diarrhea Virus Strains in Experimentally Infected Calves.

The results of experimental study of three noncytopathic and two cytopathic bovine viral diarrhea virus (BVDV) strains isolated from cattle in the Siberian region and belonging to the type 1 (subtypes 1a, 1b, and 1d) have been presented. All investigated strains caused the development of infectious process in the seronegative 4–6-month-old calves after aerosol challenge with the dose of 6 log10 TCID50. The greatest virulence had noncytopathic strain and cytopathic strain related to the subtypes 1d and 1b, respectively. All strains in infected calves caused some signs of moderate acute respiratory disease and diarrhea: depression 3–5 days postinfection (p.i.), refusal to food, severe hyperthermia to 41.9°С, serous exudate discharges from the nasal cavity and eyes, transient diarrhea with blood, leukopenia (up to 2700 cells/mm3), and macroscopic changes in the respiratory organs and intestine. The infected animals recovered from 12 to 15 days p.i. and in 90% cases formed humoral immune response 25 days p.i. (antibody titers to BVDV: 1 : 4–1 : 16). Our results confirmed the presence of virulent BVDV1 strains and showed the need for researches on the molecular epidemiology of the disease, development of more effective diagnostic systems, and optimization of control programs with use of vaccines.

Avian thermoregulation in the heat: scaling of heat tolerance and evaporative cooling capacity in three southern African arid-zone passerines.

Many birds can defend body temperature (Tb) far below air temperature (Ta) during acute heat exposure, but relatively little is known about how avian heat tolerance and evaporative cooling capacity varies with body mass (Mb), phylogeny or ecological factors. We determined maximum rates of evaporative heat dissipation and thermal end points (Tb and Ta associated with thermoregulatory failure) in three southern African ploceid passerines, the scaly-feathered weaver (Sporopipes squamifrons, Mb≈10 g), sociable weaver (Philetairus socius, Mb≈25 g) and white-browed sparrow-weaver (Plocepasser mahali, Mb≈40 g). Birds were exposed to a ramped profile of progressively increasing Ta, with continuous monitoring of behaviour and Tb used to identify the onset of severe hyperthermia. The maximum Ta birds tolerated ranged from 48°C to 54°C, and was positively related to Mb. Values of Tb associated with severe heat stress were in the range of 44 to 45°C. Rates of evaporative water loss (EWL) increased rapidly when Ta exceeded Tb, and maximum evaporative heat dissipation was equivalent to 141-222% of metabolic heat production. Fractional increases in EWL between Ta<40°C and the highest Ta reached by each species were 10.8 (S. squamifrons), 18.4 (P. socius) and 16.0 (P. mahali). Resting metabolic rates increased more gradually with Ta than expected, probably reflecting the very low chamber humidity values we maintained. Our data suggest that, within a taxon, larger species can tolerate higher Ta during acute heat stress.