High temperature (30 degrees C) blocks aerosol but not contact transmission of influenza virus

Influenza causes significant morbidity in tropical regions; however, unlike in temperate zones, influenza in the tropics is not strongly associated with a given season. We have recently shown that influenza virus transmission in the guinea pig model is most efficient under cold, dry conditions, which are rare in the tropics. Herein, we report the lack of aerosol transmission at 30 degrees C and at all humidities tested. Conversely, transmission via the contact route was equally efficient at 30 degrees C and 20 degrees C. Our data imply that contact or short-range spread predominates in the tropics and offer an explanation for the lack of a well-defined, recurrent influenza season affecting tropical and subtropical regions of the world.     

Rearing rats (Rattus norvegicus) at 30 degrees C does not alter sensitivity to noradrenaline

Rats reared from birth at 30 degrees C show a permanent deficit in body temperature regulation. To test the ability of heat-reared rats to respond to an adrenergic drive, carbon dioxide production was measured at five doses of noradrenaline in rats reared at either 20 or 30 degrees C. Noradrenaline-induced carbon dioxide production was greater at all doses in 20 degrees C rats, but sensitivity to noradrenaline was the same in heat-reared and control animals. These findings support the conclusion that the thermoregulatory deficit induced by heat rearing is due to a change induced in the nervous system.     

Fasting reduces plasma leptin-and ghrelin-immunoreactive peptide concentrations of the burbot (Lota lota) at 2 degrees C but not at 10 degrees C

The effects of fasting at two water temperatures (2 and 10 degrees C) on plasma leptin- and ghrelin-immunoreactive peptide concentrations and energy metabolism were investigated in the burbot (Lota lota), a freshwater gadoid, which lives in cold waters and tolerates long periods of fasting. Burbot were assigned to fed and fasted groups at 2 and 10 degrees C. Leptin- and ghrelin-immunoreactive peptides were identified in burbot plasma. Fasting at 2 degrees C reduced the plasma leptin- and ghrelin-immunoreactive peptide concentrations and reduced the relative liver weights and the liver and muscle glycogen concentrations. The concentrations of the leptin- and ghrelin-immunoreactivities correlated positively with each other. At 10 degrees C there were decreased plasma thyroxine levels in both sexes, and slightly lower plasma testosterone concentrations in males. The results support previous studies in stating that immunoreactivities resembling mammalian leptin and ghrelin can be detected in burbot plasma and liver, but the specific functions of these peptides will have to be determined in future studies.     

Varicella-zoster virus (VZV) ORF17 protein induces RNA cleavage and is critical for replication of VZV at 37 degrees C but not 33 degrees C

Varicella-zoster virus (VZV) open reading frame 17 (ORF17) is homologous to herpes simplex virus (HSV) UL41, which encodes the viral host shutoff protein (vhs). HSV vhs induces degradation of mRNA and rapid shutoff of host protein synthesis. An antibody to ORF17 protein detected a 46-kDa protein in VZV-infected cells. While HSV vhs is located in virions, VZV ORF17 protein was not detectable in virions. ORF17 protein induced RNA cleavage, but to a substantially lesser extent than HSV-1 vhs. Expression of ORF17 protein did not inhibit expression from a beta-galactosidase reporter plasmid, while HSV type 1 vhs abolished reporter expression. Two VZV ORF17 deletion mutants were constructed to examine the role of ORF17 in virus replication. While the ORF17 VZV mutants grew to peak titers that were similar to those of the parental virus at 33 degrees C, the ORF17 mutants grew to 20- to 35-fold-lower titers than parental virus at 37 degrees C. ORF62 protein was distributed in a different pattern in the nuclei and cytoplasm of cells infected with an ORF17 deletion mutant at 37 degrees C compared to 33 degrees C. Inoculation of cotton rats with the ORF17 deletion mutant resulted in a level of latent infection similar to that produced by inoculation with the parental virus. The importance of ORF17 protein for viral replication at 37 degrees C but not at 33 degrees C suggests that this protein may facilitate the growth of virus in certain tissues in vivo.     

Structure and function of the methanogenic archaeal community in stable cellulose-degrading enrichment cultures at two different temperatures (15 and 30 degrees C)

Methanogenic cultures were enriched from an air-dried rice field soil and incubated under anaerobic conditions at 30 degrees C with cellulose as substrate (ET1). The culture was then transferred and further incubated at either 15 degrees C (E15) or 30 degrees C (E30), to establish stable cultures that methanogenically degrade cellulose. After five transfers, the rates of CH(4) production became reproducible. At 30 degrees C, CH(4) production rates were (mean+/-S.D.) 15.2+/-0.7 nmol h(-1) ml(-1) culture for the next 16 transfers and at 15 degrees C, they were 0.38+/-0.07 nmol h(-1) ml(-1) for the next six transfers. When E30 was assayed at temperatures between 5-50 degrees C, CH(4) production rates increased with the temperature, reached a maximum at 40 degrees C and then decreased. The same temperature optimum was observed in E15, but with a lower maximum CH(4) production rate. The apparent activation energies of CH(4) production were similar (about 120 kJ mol(-1)4 mM at the beginning of the assay. The structure of the archaeal community was analyzed by molecular techniques. Total DNA was extracted from the microbial cultures before the transfer to different temperatures (ET1) and afterwards (E15, E30). The archaeal small subunit (SSU) ribosomal RNA-encoding genes (rDNA) of these DNA samples were amplified by PCR with archaeal-specific primers and characterized by terminal restriction fragment length polymorphism (T-RFLP). After obtaining a constant T-RFLP pattern in the cultural transfers at 15 and 30 degrees C, the PCR amplicons were used for the generation of clone libraries. Representative rDNA clones (n=10 for each type of culture) were characterized by T-RFLP and sequence analysis. In the primary culture (ET1), the archaeal community was dominated by clones representing 'rice cluster I', a novel lineage of methanogenic Euryarchaeota. However, further transfers resulted in the dominance of Methanosarcinaceae and Methanosaetaceae at 30 and 15 degrees C, respectively. This dominance was confirmed by fluorescence in situ hybridization (FISH) of archaeal cells. Obviously, different archaeal communities were established at the two different temperatures, but their activities nevertheless exhibited similar temperature optima.     

Gill Na+-K+-ATPase activity correlates with basolateral membrane lipid composition in seawater- but not freshwater-acclimated Arctic char (Salvelinus alpinus)

The successful migration of euryhaline teleost fish from freshwater to seawater requires the upregulation of gill Na+-K+-ATPase, an ion transport enzyme located in the basolateral membrane (BLM) of gill chloride cells. Following 39 days of seawater exposure, Arctic char had similar plasma sodium and chloride levels as individuals maintained in freshwater, indicating they had successfully acclimated to seawater. This acclimation was associated with an eightfold increase in gill Na+-K+-ATPase activity but only a threefold increase in gill Na+-K+-ATPase protein number, suggesting that other mechanisms may also modulate gill Na+-K+-ATPase activity. We therefore investigated the influence of membrane composition on Na+-K+-ATPase activity by examining the phospholipid, fatty acid, and cholesterol composition of the gill BLM from freshwater- and seawater-acclimated Arctic char. Mean gill BLM cholesterol content was significantly lower ( approximately 22%) in seawater-acclimated char. Gill Na+-K+-ATPase activity in individual seawater Arctic char was negatively correlated with BLM cholesterol content and positively correlated with %phosphatidylethanolamine and overall %18:2n6 (linoleic acid) content of the BLM, suggesting gill Na+-K+-ATPase activity of seawater-acclimated char may be modulated by the lipid composition of the BLM and may be especially sensitive to those parameters known to influence membrane fluidity. Na+-K+-ATPase activity of individual freshwater Arctic char was not correlated to any membrane lipid parameter measured, suggesting that different lipid-protein interactions may exist for char living in each environment.     

Asexual blood stages of Plasmodium falciparum exhibit signs of secondary necrosis, but not classical apoptosis after exposure to febrile temperature (40 C)

It has been shown by others that after cultures of Plasmodium falciparum were exposed to a febrile temperature of 40 C, parasitemia was reduced in the subsequent generation, suggesting a temperature-induced inhibition of trophozoites and schizonts. In the current study, influences unique to cultivation were ruled out, demonstrating that 40 C impacted the parasites directly. Metabolic profiling of DNA synthesis, protein synthesis, and glucose utilization clearly indicated that febrile temperatures had a direct effect on parasite development, beginning 20-24 hr after erythrocyte invasion. The mechanism of parasite death was investigated for evidence of temperature-induced apoptosis. Lack of typical physiological hallmarks, namely, caspase activation, characteristic mitochondrial membrane potential changes, and DNA degradation as indicated by DNA laddering, eliminated 'classical' apoptosis as a mechanism of parasite death. Parasites dying under the influence of heat, staurosporine, and chloroquine initially appeared pyknotic by light and electron microscopy (as in apoptosis), but eventual swelling and lysis of the food vacuole membrane led to secondary necrosis. Chloroquine did induce DNA laddering, but it was later attributed to occult white blood cell contaminants. While not apoptosis, the results do not rule out other forms of temperature-induced programmed cell death.