Genotyping assay for the identification of 2009-2010 pandemic and seasonal H1N1 influenza virus reassortants.

New Zealand identified its first pandemic H1N1 influenza cases in late April 2009, immediately prior to the historical start of the New Zealand influenza season. Both pandemic and oseltamivir-resistant seasonal H1N1 viruses cocirculated in the population for a period of time. Thus, concerns were raised about the possibility of reassortment events between the two strains. An RT-PCR-based genotyping assay was developed so that H1N1 influenza coinfections and reassortants could be detected quickly. The assay differentiated effectively the seasonal and pandemic strains. It also confirmed the identification of the first reported coinfection of pandemic and seasonal H1N1 strains during the 2009 Southern Hemisphere influenza season in New Zealand.

Interpreting Google flu trends data for pandemic H1N1 influenza: the New Zealand experience.

For the period of the spread of pandemic H1N1 influenza in New Zealand during 2009, we compared results from Google Flu Trends with data from existing surveillance systems. The patterns from Google Flu Trends were closely aligned with (peaking a week before and a week after) two independent national surveillance systems for influenza-like illness (ILI) cases. It was much less congruent with (delayed by three weeks) data from ILI-related calls to a national free-phone Healthline and with media coverage of pandemic influenza. Some patterns were unique to Google Flu Trends and may not have reflected the actual ILI burden in the community. Overall, Google Flu Trends appears to provide a useful free surveillance system but it should probably be seen as supplementary rather than as an alternative.

Pandemic influenza A(H1N1)v viruses currently circulating in New Zealand are sensitive to oseltamivir.

New Zealand, like other southern hemisphere countries with a temperate climate, has been in the winter period with seasonal influenza activity. New Zealand has also experienced a dramatic increase in the number of cases of pandemic influenza A(H1N1)v virus. Early reports from the northern hemisphere at the beginning of the pandemic showed that the virus was sensitive to the antiviral drug oseltamivir. In this study we report that pandemic influenza A(H1N1)v viruses currently circulating in New Zealand are sensitive to oseltamivir, but seasonal influenza A(H1N1) viruses - the co-circulating predominant seasonal strain, is resistant to oseltamivir.

An empirical quantitative framework for the seasonal population dynamics of the tick Ixodes ricinus.

The wide geographic and climatic range of the tick Ixodes ricinus, and the consequent marked variation in its seasonal population dynamics, have a direct impact on the transmission dynamics of the many pathogens vectored by this tick species. We use long-term observations on the seasonal abundance and fat contents (a marker of physiological ageing) of ticks, and contemporaneous microclimate at three field sites in the UK, to establish a simple quantitative framework for the phenology (i.e. seasonal cycle of development) of I. ricinus as a foundation for a generic population model. An hour-degree tick inter-stadial development model, driven by soil temperature and including diapause, predicts the recruitment (i.e. emergence from the previous stage) of a single cohort of each stage of ticks each year in the autumn. The timing of predicted emergence coincides exactly with the new appearance of high-fat nymphs and adults in the autumn. Thereafter, fat contents declined steadily until unfed ticks with very low energy reserves disappeared from the questing population within about 1 year from their recruitment. Very few newly emerged ticks were counted on the vegetation in the autumn, but they appeared in increasing numbers through the following spring. Larger ticks became active and subsequently left the questing population before smaller ones. Questing tick population dynamics are determined by seasonal patterns of tick behaviour, host-contact rates and mortality rates, superimposed on a basal phenology that is much less complex than has hitherto been portrayed.

Seasonal synchrony: the key to tick-borne encephalitis foci identified by satellite data.

A previous analysis of tick infestation patterns on rodents in Slovakia suggested that the key to the focal distribution of western-type tick-borne encephalitis virus (TBEv) in Europe is the geographically variable degree of synchrony in the seasonal activity of larval and nymphal Ixodes ricinus ticks. This prediction is here tested by examining records, from 7 different countries, of the seasonal variation in the abundance of larvae and nymphs feeding on rodents or questing on the vegetation. Larvae consistently started feeding and questing earlier in the year at sites within TBEv foci than elsewhere, so that they appeared in the spring as soon as nymphs were active. Such larval nymphal synchrony is associated with a rapid fall in ground-level temperatures from August to October as revealed by the satellite-derived index of Land Surface Temperature (LST). Likewise, of 1992 pixels sampled on a grid across Europe, the 418 that fell within TBEv foci were characterized by a higher than average rate of autumnal cooling relative to the peak midsummer LST. It is proposed that such a seasonal temperature profile may cause unfed larvae to pass the winter in quiescence, from which they emerge synchronously with nymphs in the spring.

Differential transmission of the genospecies of Borrelia burgdorferi sensu lato by game birds and small rodents in England.

The genetic diversity of Borrelia burgdorferi sensu lato was assessed in a focus of Lyme borreliosis in southern Britain dominated by game birds. Ticks, rodents, and pheasants were analyzed for spirochete infections by PCR-targeting the 23S-5S rRNA genes, followed by genotyping by the reverse line blot method. In questing Ixodes ricinus ticks, three genospecies of B. burgdorferi sensu lato were detected, with the highest prevalences found for Borrelia garinii and Borrelia valaisiana. B. burgdorferi sensu stricto was rare (< 1%) in all tick stages. Borrelia afzelia was not detected in any of the samples. More than 50% of engorged nymphs collected from pheasants were infected with borreliae, mainly B. garinii and/or B. valaisiana. Although 19% of the rodents harbored B. burgdorferi sensu stricto and/or B. garinii in internal organs, only B. burgdorferi sensu stricto was transmitted to xenodiagnostic tick larvae (it was transmitted to 1% of the larvae). The data indicate that different genospecies of B. burgdorferi sensu lato can be maintained in nature by distinct transmission cycles involving the same vector tick species but different vertebrate host species. Wildlife management may have an influence on the relative risk of different clinical forms of Lyme borreliosis.

Plasma membrane proton pump inhibition and stalk cell differentiation in Dictyostelium discoideum.

The choice of the stalk cell differentiation pathway in Dictyostelium is promoted by an endogenous substance, DIF-1, which is 1-(3,5-dichloro-2,6-dihydroxy-4-methoxyphenyl)-1-hexanone. It is also favoured by weak acids and two inhibitors of the plasma membrane proton pumps of fungi and plants, diethylstilbestrol (DES) and zearalenone, and antagonised by ammonia and other weak bases, which promote spore differentiation. These observations led to the proposal that the choice of differentiation pathway is regulated by intracellular pH. They also prompted the conjecture that DIF-1 itself is a plasma membrane proton pump inhibitor. We report here experiments showing that DIF-1 is not a plasma membrane proton pump inhibitor. We demonstrate that diethylstilbestrol and zearalenone do inhibit the plasma membrane proton pump of Dictyostelium and we show that there is an excellent qualitative and quantitative correlation between the inhibitory activity of these agents, and of a number of other substances, and their ability to divert differentiation from the spore to the stalk pathway. We conclude that inhibition of the plasma membrane proton pump does shift the choice of differentiation pathway in Dictyostelium towards the stalk pathway, but that DIF does not act by this route, and we propose a model for the actions of DIF and plasma membrane proton pump inhibitors in which the differentiation pathway is controlled by the pH of intracellular vesicles rather than by intracellular pH itself. The model invokes a DIF- and proton-activated vesicular chloride channel whose opening permits acidification of the vesicles and lowers cytosolic Ca++ concentration.

Intracellular pH and the control of cell differentiation in Dictyostelium discoideum.

During development in the cellular slime mould Dictyostelium discoideum starved amoebae aggregate to form multicellular structures that display a simple antero-posterior pattern: prestalk cells occupy the front 20% of the aggregate, and prespore cells occupy the remainder. We have attempted to elucidate the nature of the mechanism regulating the proportions of the two cell types by examining the factors that influence the pathway of differentiation of amoebae in vitro. Amoebae of D. discoideum strain V12 M2 form stalk cells efficiently in appropriate conditions and 'sporogenous' derivatives produce spores as well as stalk cells. Mature spores are formed in a medium containing only cyclic AMP and salts, whereas formation of stalk cells requires, in addition, a low molecular weight hydrophobic factor (DIF). Recent observations have led us to propose that DIF is a morphogen responsible for activating stalk cell differentiation. Here we present evidence that ammonia is a second morphogen, that acts antagonistically to DIF, and that the choice of differentiation pathway is mediated by intracellular pH.

Cell patterning in Dictyostelium.

We summarize studies on stalk and spore cell formation in D. discoideum cell monolayers, aimed at revealing factors involved in controlling the prestalk:prespore pattern in this organism. We propose that there are no cell interactions dependent on cell contact per se. Formation of mature stalk cells from isolated amoebae incubated in a buffered salts medium requires only cyclic AMP and a lipid-like factor (DIF) released by cells developing at high density. In addition, a variety of sporogenous mutants can form spores rapidly and efficiently when incubated at low density in tissue culture dishes containing a similar cyclic AMP and salts medium. In some cases spore formation is improved by the addition of one or other of a variety of protective agents such as bovine serum albumin. Wild-type amoebae at low density form prespore cells under the same conditions. We present some evidence that DIF is the activator of prestalk cell formation in a two-component patterning mechanism of the kind proposed by Wolpert et al. (Symp. Soc. exp. Biol. 25, 391-415 (1971)) and Gierer & Meinhardt (Kybernetik 12, 30-39 (1972)). We also provide data indicating that the role of inhibitor is played by ammonia, an idea first mooted by Sussman & Schindler (Differentiation 10, 1-5 (1978)).

Signal emission and signal propagation during early aggregation in Dictyostelium discoideum.

Waves of chemotactic movement during the early phase of aggregation in Dictyostelium discoideum are of 2 kinds, concentric waves produced by cells that emit cyclic AMP signals spontaneously, and spirals generated by excitations relayed continuously around loops of excitable cells. The period of a spiral wave is the time taken for the excitation to make one complete circuit of the pacemaker loop. We have compared signal emission from the 2 types of source in time-lapse films made at a variety of temperatures. Our results show that spiral waves have a characteristic period length throughout most if not all of the early phase of aggregation, and that the period of concentric waves is generally longer and more variable. Temperature has a pronounced effect on period length and a lesser effect on propagation velocity. We find that each individual wave is propagated at constant velocity over distances of 1-2 cm but that the velocity of successive waves declines. This decline probably reflects some cumulative effect of the chemotactic excitations on the excitable properties of the aggregating cells.