What is the real number of Lyme disease cases in Canada?

BACKGROUND

Lyme disease is emerging in Canada due to expansion of the range of the tick vector Ixodes scapularis from the United States. National surveillance for human Lyme disease cases began in Canada in 2009. Reported numbers of cases increased from 144 cases in 2009 to 2025 in 2017. It has been claimed that few (< 10%) Lyme disease cases are reported associated with i) supposed under-diagnosis resulting from perceived inadequacies of serological testing for Lyme disease, ii) expectation that incidence in Canadian provinces and neighbouring US states should be similar, and iii) analysis of serological responses of dogs to the agent of Lyme disease, Borrelia burgdorferi. We argue that performance of serological testing for Lyme disease is well studied, and variations in test performance at different disease stages are accounted for in clinical diagnosis of Lyme disease, and in surveillance case definitions. Extensive surveillance for tick vectors has taken place in Canada providing a clear picture of the emergence of risk in the Canadian environment. This surveillance shows that the geographic scope of I. scapularis populations and Lyme disease risk is limited but increasing in Canada. The reported incidence of Lyme disease in Canada is consistent with this pattern of environmental risk, and the differences in Lyme disease incidence between US states and neighbouring Canadian provinces are consistent with geographic differences in environmental risk. Data on serological responses in dogs from Canada and the US are consistent with known differences in environmental risk, and in numbers of reported Lyme disease cases, between the US and Canada.

CONCLUSION

The high level of consistency in data from human case and tick surveillance, and data on serological responses in dogs, suggests that a high degree of under-reporting in Canada is unlikely. We speculate that approximately one third of cases are reported in regions of emergence of Lyme disease, although prospective studies are needed to fully quantify under-reporting. In the meantime, surveillance continues to identify and track the ongoing emergence of Lyme disease, and the risk to the public, in Canada.

Increased risk of endemic mosquito-borne diseases in Canada due to climate change

There are currently over 80 species of mosquito endemic in Canada-although only a few of these carry pathogens that can cause disease in humans. West Nile virus, Eastern equine encephalitis virus and the California serogroup viruses (including the Jamestown Canyon and snowshoe hare viruses) are mosquito-borne viruses that have been found to cause human infections in North America, including in Canada. Over the last 20 years, the incidence of most of these endemic mosquito-borne diseases (MBD) has increased approximately 10% in Canada, due in large part to climate change. It is anticipated that both the mosquito lifecycle and virus transmission patterns will be affected by climate change, resulting in an increase in both the range and local abundance of several important mosquito species. Laboratory studies and mathematical modelling suggest that increased ambient temperatures, changes in precipitation and extreme weather events associated with climate change will likely continue to drive mosquito vector and MBD range expansion, increasing the duration of transmission seasons and leading to MBD-related epidemics. Furthermore, Canada's endemic MBDs have complex transmission cycles, involving multiple reservoir hosts (birds and mammals), multiple pathogens and multiple mosquito species-all of which may be sensitive to climate and other environmental changes, and making forecasting of potential emerging trends difficult. These expected climate-induced changes in mosquitoes and MBDs underline the need for continued (and expanded) surveillance and research to ensure timely and accurate evaluation of the risks to the public health of Canadians.

Could exotic mosquito-borne diseases emerge in Canada with climate change?

Of the 3,500 species of mosquitoes worldwide, only a small portion carry and transmit the mosquito-borne diseases (MBDs) that cause approximately half a million deaths annually worldwide. The most common exotic MBDs, such as malaria and dengue, are not currently established in Canada, in part because of our relatively harsh climate; however, this situation could evolve with climate change. Mosquitoes native to Canada may become infected with new pathogens and move into new regions within Canada. In addition, new mosquito species may move into Canada from other countries, and these exotic species may bring exotic MBDs as well. With high levels of international travel, including to locations with exotic MBDs, there will be more travel-acquired cases of MBDs. With climate change, there is the potential for exotic mosquito populations to become established in Canada. There is already a small area of Canada where exotic Aedes mosquitoes have become established although, to date, there is no evidence that these carry any exotic (or already endemic) MBDs. The increased risks of spreading MBDs, or introducing exotic MBDs, will need a careful clinical and public health response. Clinicians will need to maintain a high level of awareness of current trends, to promote mosquito bite prevention strategies, and to know the laboratory tests needed for early detection and when to report laboratory results to public health. Public health efforts will need to focus on ongoing active surveillance, public and professional awareness and mosquito control. Canadians need to be aware of the risks of acquiring exotic MBDs while travelling abroad as well as the risk that they could serve as a potential route of introduction for exotic MBDs into Canada when they return home.

Emerging mosquito-borne bunyaviruses in Canada

California serogroup and Cache Valley viruses are arboviruses (tick- and mosquito-borne pathogens) belonging to the genus Orthobunyavirus (Family Bunyaviridae). Although the majority of exposures to these viruses result in asymptomatic or mild infections, both California serogroup and Cache Valley viruses can cause febrile and neurological diseases similar in nature to those associated with infections by West Nile virus. California serogroup and Cache Valley viruses are widely distributed across North America and circulate in a number of vertebrate hosts and mosquito vectors, including several species of Aedes and other non-Culex mosquitoes. The Jamestown Canyon and snowshoe hare viruses are the most common kind of California serogroup viruses found in Canada and have been identified throughout the country. These potential pathogens may be contributing to a higher burden of illness than previously recognized and should be considered as part of the differential diagnosis for febrile and neuroinvasive disease during the mosquito season. Diagnosis can be made by requesting a diagnostic panel at the Viral Zoonoses program at the National Microbiology Laboratory. To decrease the risk of infection, education about these viruses and the importance of personal preventive measures is warranted.

Travel-related chikungunya cases in Canada, 2014

Since the spring of 2014, there has been a large increase in travel-related chikungunya cases diagnosed in Canada. As of December 9, 2014, 320 confirmed and 159 probable cases have been diagnosed in Canada, with the majority of provinces identifying at least one imported case. This surge in Canadian infections has been associated with the incursion of chikungunya virus into the Caribbean and the expansion of the virus in the Americas. Ongoing outbreaks in the Asia-Pacific region have also contributed to imported cases among Canadian travellers. Heightened awareness of chikungunya among clinicians is key to diagnosis. This highlights the need to ask for a travel history from anyone who presents with fever or recent onset of polyarthralgia, and to consider testing by provincial laboratories and the National Microbiology Laboratory for chikungunya virus and other diseases as indicated. Also essential is continued communication with travellers regarding the use of preventative measures to decrease the risk of exposure to mosquitoes when travelling to endemic areas.

Ixodes scapularis ticks collected by passive surveillance in Canada: analysis of geographic distribution and infection with Lyme borreliosis agent Borrelia burgdorferi

Passive surveillance for the occurrence of the tick Ixodes scapularis Say (1821) and their infection with the Lyme borreliosis spirochaetes Borrelia burgdorferi s.l. has taken place in Canada since early 1990. Ticks have been submitted from members of the public, veterinarians, and medical practitioners to provincial, federal, and university laboratories for identification, and the data have been collated and B. burgdorferi detected at the National Microbiology Laboratory. The locations of collection of 2,319 submitted I. scapularis were mapped, and we investigated potential risk factors for I. scapularis occurrence (in Quebec as a case study) by using regression analysis and spatial statistics. Ticks were submitted from all provinces east of Alberta, most from areas where resident I. scapularis populations are unknown. Most were adult ticks and were collected in spring and autumn. In southern Québec, risk factors for tick occurrence were lower latitude and remote-sensed indices for land cover with woodland. B. burgdorferi infection, identified by conventional and molecular methods, was detected in 12.5% of 1,816 ticks, including 10.1% of the 256 ticks that were collected from humans and tested. Our study suggests that B. burgdorferi-infected I. scapularis can be found over a wide geographic range in Canada, although most may be adventitious ticks carried from endemic areas in the United States and Canada by migrating birds. The risk of Lyme borreliosis in Canada may therefore be mostly low but more geographically widespread than previously suspected.

Ixodes scapularis ticks collected by passive surveillance in Canada: analysis of geographic distribution and infection with Lyme borreliosis agent Borrelia burgdorferi

Passive surveillance for the occurrence of the tick Ixodes scapularis Say (1821) and their infection with the Lyme borreliosis spirochaetes Borrelia burgdorferi s.l. has taken place in Canada since early 1990. Ticks have been submitted from members of the public, veterinarians, and medical practitioners to provincial, federal, and university laboratories for identification, and the data have been collated and B. burgdorferi detected at the National Microbiology Laboratory. The locations of collection of 2,319 submitted I. scapularis were mapped, and we investigated potential risk factors for I. scapularis occurrence (in Quebec as a case study) by using regression analysis and spatial statistics. Ticks were submitted from all provinces east of Alberta, most from areas where resident I. scapularis populations are unknown. Most were adult ticks and were collected in spring and autumn. In southern Québec, risk factors for tick occurrence were lower latitude and remote-sensed indices for land cover with woodland. B. burgdorferi infection, identified by conventional and molecular methods, was detected in 12.5% of 1,816 ticks, including 10.1% of the 256 ticks that were collected from humans and tested. Our study suggests that B. burgdorferi-infected I. scapularis can be found over a wide geographic range in Canada, although most may be adventitious ticks carried from endemic areas in the United States and Canada by migrating birds. The risk of Lyme borreliosis in Canada may therefore be mostly low but more geographically widespread than previously suspected.

Use of immunoglobulin G avidity assays for differentiation of primary from previous infections with West Nile virus

Since its introduction in 1999, West Nile virus (WNV) infections have spread rapidly across the North American continent. Diagnosis of acute WNV infection by detection of WNV-specific immunoglobulin M (IgM) is complicated by the persistence of detectable IgM for more than 1 year in some patients. IgG antibody avidity testing was assessed as a supplemental assay in the diagnosis of current infections. Three groups of serum samples were assayed in parallel by two different IgG avidity test systems (indirect immunofluorescence test [IIFT] and prototype enzyme-linked immunosorbent assay [ELISA]; EUROIMMUN, Luebeck, Germany). Group I (40 sera taken between 2 and 9 days after the onset of influenza-like symptoms) and group II (40 sera taken between 10 and 43 days after onset) were acute and convalescent specimens from patients with a positive anti-WNV IgM test (ELISA; Focus Diagnostics, Cypress, CA). Group III consisted of 43 patient sera collected between 6 and 12 months after infection. IgG antibodies specific for WNV were detected in 38% (ELISA) and 50% (IIFT) of group I sera, in 90% (ELISA and IIFT) of group II sera, and in 100% (ELISA and IIFT) of group III sera. Low-avidity IgG antibodies were demonstrated in 86% (ELISA) and 95% (IIFT) of IgG-positive patient samples taken between 2 and 43 days after the onset of symptoms (groups I and II). High-avidity IgG antibodies were detected in 100% of group III sera obtained 6 months or more after the onset of symptoms (ELISA and IIFT). IgG avidity tests for WNV infections are rapid and simple to perform. The determination of IgG avidity provides additional diagnostic certainty in differentiating between recently acquired and previous infections with WNV.

Genetic and serotypic characterization of Sin Nombre-like viruses in Canadian Peromyscus maniculatus mice

In Canada, hantavirus infected deer mice (Peromyscus maniculatus) have been collected from British Columbia to Newfoundland. Partial sequencing of G1 and N protein encoding regions from Canadian Peromyscus maniculatus-borne hantaviruses demonstrated the existence of significant genotypic divergence among strains. Phylogenetic analysis showed that Sin Nombre (SN)-like viruses from eastern and western Canadian deer mice can be divided into at least two broad-based genogroups. Sequencing of mitochondrial DNA from infected deer mice originating from various eastern and western provinces showed that SN-like virus genogroups appeared to be associated with distinct haplotypes of mice. Sera from deer mice infected with eastern and western viral genotypes neutralized the Sin Nombre virus strain, Convict Creek 107, but not the New York 1 hantavirus. Despite the genetic heterogeneity of Canadian SN-like strains these hantaviruses do not appear to define unique hantavirus serotypes.

A genotypic characterization of enteroviral antigenic variants isolated in eastern Canada

Antigenic variation within serotypes of enteroviruses can have a significant impact on the effectiveness of routine diagnosis by neutralization assays. The focus of this particular study was to initiate a genetic characterization of echovirus type 9 (E9) antigenic variants and nontypeable strains isolated in Canada from 1991 to 1993. All variant strains were initially identified by the serological parameter of neutralization 'breakthrough' during conventional serotyping using the Lim-Benyesh-Melnick antiserum pools and by assessing neutralization endpoints using micro-neutralization methodology. Both E9 variant and non-variant isolates were further characterized by sequencing amplicons generated from the VP2 capsid protein-coding region of these particular strains. Variants from the provinces of Ontario and New Brunswick were shown to include a number of genotypically distinct strains and all the variant strains were significantly different from non-variant E9 isolates when nucleotide sequences were compared. A similar genetic analysis of two completely non-typeable isolates from Quebec showed that these viruses seemed to belong to a genetic cluster of enteroviruses that included coxsackievirus A16 and enterovirus 71 serotypes. The use of genetic typing by sequence analysis provides a molecular tool for determining the genotypic diversity of variant and non-typeable isolates and their possible relatedness to other enteroviral strains.

Outbreak of viral gastroenteritis due to a contaminated well. International consequences

CONTEXT

Small round-structured viruses (SRSVs) are known to cause viral gastroenteritis, but until now have not been confirmed in the implicated vehicle in outbreaks.

OBJECTIVE

Investigation of a gastroenteritis outbreak.

DESIGN

After applying epidemiologic methods to locate the outbreak source, we conducted environmental and laboratory investigations to elucidate the cause.

SETTING

Tourists traveling by bus through Alaska and the Yukon Territory of Canada.

PARTICIPANTS

Staff of a restaurant at a business complex implicated as the outbreak source, convenience sample of persons on buses that had stopped there, and bus employees.

MAIN OUTCOME MEASURES

Odds ratios (ORs) for illness associated with exposures. Water samples from the restaurant and stool specimens from tourists and restaurant staff were examined by nucleic acid amplification using reverse transcription polymerase chain reaction and sequencing of viral amplification products.

RESULTS

The itineraries of groups of tourists manifesting vomiting or diarrhea were traced back to a restaurant where buses had stopped 33 to 36 hours previously. Water consumption was associated with illness (OR, 5.3; 95% confidence interval [CI], 2.3-12.6). Eighteen of 26 employees of the business complex were ill; although not the index case, an employee ill shortly before the outbreak lived in a building connected to a septic pit, which was found to contaminate the well supplying the restaurant's water. Genotype 2/P2B SRSV was identified in stool specimens of 2 tourists and 1 restaurant employee. Stools and water samples yielded identical amplification product sequences.

CONCLUSIONS

The investigation documented SRSVs in a vehicle epidemiologically linked to a gastroenteritis outbreak. The findings demonstrate the power of molecular detection and identification and underscore the importance of fundamental public health practices such as restaurant inspection, assurance of a safe water supply, and disease surveillance.

Identification and characterization of IS1476, an insertion sequence-like element that disrupts VanY function in a vancomycin-resistant Enterococcus faecium strain

The vanY gene of vancomycin-resistant enterococci encodes a D,D-carboxypeptidase. By using a PCR detection strategy, a VanA Enterococcus faecium clinical isolate was found to have an insertion sequence (IS)-like element designated IS1476 in vanY. The activity of the VanY D,D-carboxypeptidase in this isolate was decreased in a fluorometric fluoraldehyde o-phthalaldehyde assay with diacetyl-L-Lys-D-Ala-D-Ala as the substrate. This, to our knowledge, is the first report of an IS-like element in a vancomycin resistance gene.

Molecular detection of an importation of type 3 wild poliovirus into Canada from The Netherlands in 1993

During the fall and winter of 1992-1993 an outbreak of wild poliovirus type 3-associated poliomyelitis involving 71 patients occurred in The Netherlands. Almost all of the individuals involved in the outbreak belonged to an orthodox religious denomination that prohibits vaccination. A surveillance was initiated to determine if there had been an importation of this same strain of wild poliovirus into a southern Alberta community with a similar religious affiliation. Viral culture of stool samples from consenting individuals in the community resulted in viral isolates which typed as poliovirus type 3. Sequencing of amplicons generated from both the 5' nontranslated region and the VP1/2A portion of the genomes from representative poliovirus isolates indicated a greater than 99% genetic similarity to the strain from The Netherlands. The results of this study show that the utilization of PCR-based diagnostics offers an important molecular tool for the concise and rapid surveillance of possible cases of wild poliovirus importation into communities with individuals at risk for infection.

Molecular characterization of a wild poliovirus type 3 epidemic in The Netherlands (1992 and 1993)

An outbreak of poliomyelitis due to wild poliovirus type 3 (PV3) occurred in an unvaccinated community in The Netherlands between September 1992 and February 1993. The outbreak involved 71 patients. The aim of this study was to characterize the virus at the molecular level and to analyze the molecular evolution of the epidemic virus. Molecular analysis was carried out by sequencing the VP1/2A junction region (150 nucleotides) of 50 PV3 strains isolated in association with this outbreak and the entire VP1 gene of 14 strains. In addition, the sequence of the VP1/2A junction region of strains from geographical regions endemic for PV3 (Egypt, India, and Central Asia) was analyzed and compared with the nucleotide sequence of the epidemic strain from The Netherlands. The earliest isolate was obtained from river water sampled 3 weeks before diagnosis of the first poliomyelitis patient and was found by VP1/2A sequence analysis to be genetically identical to the strain isolated from the first patient. Sequence divergence among the strains from the epidemic in The Netherlands was less than 2%. The closest genetic similarity (97.3%) was found with an Indian isolate (New Delhi, December 1991), indicating the likely source of the virus. A more than 99% sequence similarity was found in the VP1/2A region. Finally, the sequence information was used to design primers for the specific and highly sensitive molecular detection of PV3 strains during the epidemic.

Molecular epidemiology of enterovirus outbreaks in Canada during 1991-1992: identification of echovirus 30 and coxsackievirus B1 strains by amplicon sequencing

The relatedness of enteroviral isolates associated with two recent outbreaks in Canada was assessed using direct sequencing of amplicons derived from a large portion of the 5' nontranslated region (NTR) of the viral genome. The amplicons of 60 echovirus 30 isolates originating from seven different provinces in 1991 were found to share 99% or greater sequence identity. Recent coxsackievirus B1 isolates characterised in the same manner were identical to each other. When the 5' NTR sequence of these isolates was compared to prototype strains a difference of 11-15% in nucleotide composition was observed. These results indicate that the variability of nucleotide sequence found in 5' NTRs can be utilized to identify rapidly enteroviral strains associated with particular outbreaks and distinguish them from other strains and serotypes.

A member of a novel family of yeast ‘zn-finger’ proteins mediates the transition from stationary phase to cell proliferation

The cloning and molecular characterization of the GCS1 gene from the budding yeast Saccharomyces cerevisiae show that stationary phase is in fact a unique developmental state, with requirements to resume cell proliferation that can be distinct from those for maintenance of proliferation. Deletion of the GCS1 gene products a novel phenotype: stationary-phase mutant cells do not resume proliferation at a restrictive temperature of 15 degrees C, but mutant cells lacking Gcs1p that are proliferating at the permissive temperature of 29 degrees C continue to proliferate after transfer to 15 degrees C as long as nutrients are available. The GCS1 gene sequence predicts a 39 kDa polypeptide with a novel 'Zn-finger' motif. A point mutation within the finger motif produces a phenotype that mimics that of deletion of the GCS1 gene, showing that the finger motif is essential for full Gcs1p activity. Gcs1p and the products of two newly identified genes, SPS18 and GLO3, constitute a family of novel Zn-finger proteins.

An impaired RNA polymerase II activity in Saccharomyces cerevisiae causes cell-cycle inhibition at START

Saccharomyces cerevisiae cells harboring the temperature-sensitive mutation rpo21-4, in the gene encoding the largest subunit of RNA polymerase II, were shown to be partially impaired for cell-cycle progress at a permissive temperature, and to become permanently blocked at the cell-cycle regulatory step, START, at a restrictive temperature. The rpo21-4 mutation was lethal in combination with cdc28 mutations in the p34 protein kinase gene required for START. Transcripts of the CLN1 and CLN2 genes, encoding G1-cyclin proteins that, along with p34, are necessary for START, were decreased in abundance by the rpo21-4 mutation at a restrictive temperature. Increased G1-cyclin production, by expression of the CLN1 or CLN2 genes from a heterologous GAL promoter, overcame the rpo21-4-mediated START inhibition, but such mutant cells nevertheless remained unable to proliferate at a restrictive temperature. These findings reveal that START can be particularly sensitive to an impaired RNA polymerase II function, presumably through effects on G1-cyclin expression.

Mitochondrial DNA loss by yeast reentry-mutant cells conditionally unable to proliferate from stationary phase

Double-mutant cells of the budding yeast Saccharomyces cerevisiae harboring the gcs1-1 and sed1-1 mutations are conditionally defective (cold-sensitive) only for reentry into the mitotic cycle from stationary phase. If already proliferating at the permissive temperature (29 degrees C), these reentry-mutant cells continue to proliferate when transferred to the restrictive temperature of 14 degrees C, but under these conditions reentry-mutant cells lose mitochondrial DNA (mtDNA). In addition, upon exhaustion of the nutrient supply at 14 degrees C, these reentry-mutant cells entered stationary phase at a decreased cell concentration and did not accumulate the reserve carbohydrates trehalose and glycogen. Both of these deficiencies were due to the loss of mtDNA, as shown by the responses of wild-type cells also lacking mtDNA. Mitochondrial status did not affect other aspects of the reentry-mutant phenotype. Although mitochondrial activity and the accumulation of carbohydrate reserves are typical features of cells in stationary phase, the reentry-mutant phenotype reveals that neither entry into nor exit from stationary phase need involve mitochondrial function.

Isolation and phenotypic analysis of conditional-lethal, linker-insertion mutations in the gene encoding the largest subunit of RNA polymerase II in Saccharomyces cerevisiae

Linker-insertion mutagenesis was used to isolate mutations in the Saccharomyces cerevisiae gene encoding the largest subunit of RNA polymerase II (RPO21, also called RPB1). The mutant rpo21 alleles carried on a plamid were introduced into a haploid yeast strain that conditionally expresses RPO21 from the inducible promoter pGAL10. Growth of this strain on medium containing glucose is sustained only if the plasmid-borne rpo21 allele encodes a functional protein. Of nineteen linker-insertion alleles tested, five (rpo21-4 to -8) were found that impose a temperature-sensitive (ts) lethal phenotype on yeast cells. Four of these five ts alleles encode mutant proteins in which the site of insertion lies near one of the regions of the largest subunit that have been conserved during evolution. Two of the ts mutants (rpo21-4 and rpo21-7) display pleiotropic phenotypes, including an auxotrophy for inositol and a decreased proliferation rate at the permissive temperature. The functional relationship between RPO21 and RPO26, the gene encoding the 17.9 kDa subunit shared by RNA polymerases I, II, and III was investigated by determining the ability of increased dosage of RPO26 to suppress the ts phenotype imposed by rpo21-4 to -8. Suppression of the ts defect was specific for the rpo21-4 allele and was accompanied by co-suppression of the inositol auxotrophy. These results suggest that mutations in the largest subunit of RNA polymerase II can have profound effects on the expression of specific subsets of genes, such as those involved in the metabolism of inositol. In the rpo21-4 mutant, these pleiotropic phenotypes can be attributed to a defective interaction between the largest subunit and the RPO26 subunit of RNA polymerase II.

Induction of yeast histone genes by stimulation of stationary-phase cells

In the cell cycle of the budding yeast Saccharomyces cerevisiae, expression of the histone genes H2A and H2B of the TRT1 and TRT2 loci is regulated by the performance of "start," the step that also regulates the cell cycle. Here we show that histone production is also subject to an additional form of regulation that is unrelated to the mitotic cell cycle. Expression of histone genes, as assessed by Northern (RNA) analysis, was shown to increase promptly after the stimulation, brought about by fresh medium, that activates stationary-phase cells to reenter the mitotic cell cycle. The use of a yeast mutant that is conditionally blocked in the resumption of proliferation at a step that is not part of the mitotic cell cycle (M.A. Drebot, G.C. Johnston, and R.A. Singer, Proc. Natl. Acad. Sci. 84:7948, 1987) showed that this increased gene expression that occurs upon stimulation of stationary-phase cells took place in the absence of DNA synthesis and without the performance of start. This stimulation-specific gene expression was blocked by the mating pheromone alpha-factor, indicating that alpha-factor directly inhibits expression of these histone genes, independently of start.

Genetic assessment of stationary phase for cells of the yeast Saccharomyces cerevisiae

Starvation of cells of the yeast Saccharomyces cerevisiae causes cessation of proliferation and acquisition of characteristic physiological properties. The stationary-phase state that results represents a unique developmental state, as shown by a novel conditional phenotype (M. A. Drebot, G. C. Johnston, and R. A. Singer, Proc. Natl. Acad. Sci. USA 84:7948-7952, 1987): mutant cells cannot proliferate at the restrictive temperature when stimulated to reenter the mitotic cell cycle from stationary phase but are unaffected and continue proliferation indefinitely if transferred to the restrictive temperature during exponential growth. We have exploited this reentry mutant phenotype to demonstrate that the same stationary-phase state is generated by nitrogen, sulfur, or carbon starvation and by the cdc25-1 mutation, which conditionally impairs the cyclic AMP-mediated signal transduction pathway. We also show that heat shock, a treatment that elicits physiological perturbations associated with stationary phase, does not cause cells to enter stationary phase. The physiological properties associated with stationary phase therefore do not result from residence in stationary phase but from the stress conditions that bring about stationary phase.

A yeast mutant conditionally defective only for reentry into the mitotic cell cycle from stationary phase

We report the isolation of a cold-sensitive mutant of the yeast Saccharomyces cerevisiae that is conditionally defective only for reentry into the mitotic cell cycle from stationary phase. Although actively dividing mutant cells shifted to the restrictive temperature continued to divide, stationary-phase mutant cells placed in fresh medium at the restrictive temperature failed to divide or even perform the cell cycle regulatory step "start" but did lose the characteristic stationary-phase properties of thermotolerance, accumulation of storage carbohydrates, and resistance to cell-wall-lytic enzymes. Order-of-function analysis indicated that the cold-sensitive defect blocked cells during reentry before start of the first mitotic cell cycle. Genetic analysis showed that the mutant phenotype is due to the interaction between two mutations, a cold-sensitive mutation gcs1 and a suppressor mutation sed1. These mutations thus provide the genetic basis for further analysis of stationary phase and the G0 state.

Differential effect of interferon on glycoprotein and membrane protein of vesicular stomatitis virus released from murine and simian cells

Previous studies by Maheshwari et al. have indicated that vesicular stomatitis virus (VSV) released from interferon (IFN)-treated mouse L-929 (L) cells was structurally defective. Such virions had significantly smaller amounts of glycoprotein (G) and membrane protein (M). Olden et al. recently reported, however, that they were not able to repeat the findings of Maheshwari et al. We have examined the effect of IFN on VSV released from three different cell lines and observed that treatment of L-cells and secondary mouse embryo (ME) cells with an amount of mouse IFN that reduced infectious virus yield 100-fold, led to the release of VSV with reduced amounts of G and M proteins. However, at concentrations of IFN less than this concentration, this effect was not observed. In contrast, VSV released from human (Hu)IFN-treated primate BSC-1, cells showed no reduction in their G and M protein even at concentrations resulting in 400-fold decreases in infectious virus yield.