Incidence of plague associated with increased winter-spring precipitation in New Mexico

Climate change effects on plague and tularemia in the United States

Plague and tularemia are serious zoonotic diseases endemic to North America. We evaluated spatial patterns in their transmission in view of changing climates. First, we tested whether observed shifts since the 1960s are consistent with expected patterns of shift given known climate changes over that period. Then, we used general circulation model results summarizing global patterns of changing climates into the future to forecast likely shifts in patterns of transmission over the next 50 years. The results indicate that these diseases are indeed shifting in accord with patterns of climatic shift, but that overall geographic shifts will likely be subtle, with some northward movement of southern limits and possibly northward movement of northern limits as well.

Climate and vectorborne diseases

Climate change could significantly affect vectorborne disease in humans. Temperature, precipitation, humidity, and other climatic factors are known to affect the reproduction, development, behavior, and population dynamics of the arthropod vectors of these diseases. Climate also can affect the development of pathogens in vectors, as well as the population dynamics and ranges of the nonhuman vertebrate reservoirs of many vectorborne diseases. Whether climate changes increase or decrease the incidence of vectorborne diseases in humans will depend not only on the actual climatic conditions but also on local nonclimatic epidemiologic and ecologic factors. Predicting the relative impact of sustained climate change on vectorborne diseases is difficult and will require long-term studies that look not only at the effects of climate change but also at the contributions of other agents of global change such as increased trade and travel, demographic shifts, civil unrest, changes in land use, water availability, and other issues. Adapting to the effects of climate change will require the development of adequate response plans, enhancement of surveillance systems, and development of effective and locally appropriate strategies to control and prevent vectorborne diseases.

Disease emergence from global climate and land use change

Climate change and land use change can affect multiple infectious diseases of humans, acting either independently or synergistically. Expanded efforts in empiric and future scenario-based risk assessment are required to anticipate problems. Moreover, the many health impacts of climate and land use change must be examined in the context of the myriad other environmental and behavioral determinants of disease. To optimize prevention capabilities, upstream environmental approaches must be part of any intervention, rather than assaults on single agents of disease. Clinicians must develop stronger ties, not only to public health officials and scientists, but also to earth and environmental scientists and policy makers. Without such efforts, we will inevitably benefit our current generation at the cost of generations to come.

Geographic distribution and ecological niche of plague in sub-Saharan Africa

BACKGROUND

Plague is a rapidly progressing, serious illness in humans that is likely to be fatal if not treated. It remains a public health threat, especially in sub-Saharan Africa. In spite of plague's highly focal nature, a thorough ecological understanding of the general distribution pattern of plague across sub-Saharan Africa has not been established to date. In this study, we used human plague data from sub-Saharan Africa for 1970-2007 in an ecological niche modeling framework to explore the potential geographic distribution of plague and its ecological requirements across Africa.

RESULTS

We predict a broad potential distributional area of plague occurrences across sub-Saharan Africa. General tests of model's transferability suggest that our model can anticipate the potential distribution of plague occurrences in Madagascar and northern Africa. However, generality and predictive ability tests using regional subsets of occurrence points demonstrate the models to be unable to predict independent occurrence points outside the training region accurately. Visualizations show plague to occur in diverse landscapes under wide ranges of environmental conditions.

CONCLUSION

We conclude that the typical focality of plague, observed in sub-Saharan Africa, is not related to fragmented and insular environmental conditions manifested at a coarse continental scale. However, our approach provides a foundation for testing hypotheses concerning focal distribution areas of plague and their links with historical and environmental factors.

Risk communication planning for the aftermath of a plague bioattack

We create an influence diagram of how a plague bioattack could unfold and then use it to identify factors shaping infection risks in many possible scenarios. The influence diagram and associated explanations provide a compact reference that allows risk communicators to identify key messages for pre-event preparation and testing. It can also be used to answer specific questions in whatever unique situations arise, considering both the conditions of the attack and the properties of the attacked populations. The influence diagram allows a quick, visual check of the factors that must be covered when evaluating audience information needs. The documentation provides content for explaining the resultant advice. We show how these tools can help in preparing for crises and responding to them.

Climate-driven spatial dynamics of plague among prairie dog colonies

We present a Bayesian hierarchical model for the joint spatial dynamics of a host-parasite system. The model was fitted to long-term data on regional plague dynamics and metapopulation dynamics of the black-tailed prairie dog, a declining keystone species of North American prairies. The rate of plague transmission between colonies increases with increasing precipitation, while the rate of infection from unknown sources decreases in response to hot weather. The mean annual dispersal distance of plague is about 10 km, and topographic relief reduces the transmission rate. Larger colonies are more likely to become infected, but colony area does not affect the infectiousness of colonies. The results suggest that prairie dog movements do not drive the spread of plague through the landscape. Instead, prairie dogs are useful sentinels of plague epizootics. Simulations suggest that this model can be used for predicting long-term colony and plague dynamics as well as for identifying which colonies are most likely to become infected in a specific year.

A quadruplex real-time PCR assay for the detection of Yersinia pestis and its plasmids

Yersinia pestis, the aetiological agent of the plague, causes sporadic disease in endemic areas of the world and is classified as a National Institute of Allergy and Infectious Diseases Category A Priority Pathogen because of its potential to be used as a bioweapon. Health departments, hospitals and government agencies need the ability to rapidly identify and characterize cultured isolates of this bacterium. Assays have been developed to perform this function; however, they are limited in their ability to distinguish Y. pestis from Yersinia pseudotuberculosis. This report describes the creation of a real-time PCR assay using Taqman probes that exclusively identifies Y. pestis using a unique target sequence of the yihN gene on the chromosome. As with other Y. pestis PCR assays, three major genes located on each of the three virulence plasmids were included: lcrV on pCD1, caf1 on pMT1 and pla on pPCP1. The quadruplex assay was validated on a collection of 192 Y. pestis isolates and 52 near-neighbour isolates. It was discovered that only 72 % of natural plague isolates from the states of New Mexico and Utah harboured all three virulence plasmids. This quadruplex assay proved to be 100 % successful in differentiating Y. pestis from all near neighbours tested and was able to reveal which of the three virulence plasmids a particular isolate possessed.

Plague: past, present, and future

The authors argue that plague should be taken much more seriously by the international health community.

Human plague in the southwestern United States, 1957-2004: spatial models of elevated risk of human exposure to Yersinia pestis

Plague is a rare but highly virulent flea-borne zoonotic disease caused by the Gram-negative bacterium Yersinia pestis Yersin. Identifying areas at high risk of human exposure to the etiological agent of plague could provide a useful tool for targeting limited public health resources and reduce the likelihood of misdiagnosis by raising awareness of the disease. We created logistic regression models to identify landscape features associated with areas where humans have acquired plague from 1957 to 2004 in the four-corners region of the United States (Arizona, Colorado, New Mexico, and Utah), and we extrapolated those models within a geographical information system to predict where plague cases are likely to occur within the southwestern United States disease focus. The probability of an area being classified as high-risk plague habitat increased with elevation up to approximately 2300 m and declined as elevation increased thereafter, and declined with distance from key habitat types (e.g., southern Rocky Mountain piñon--juniper [Pinus edulis Engelm. and Juniperus spp.], Colorado plateau piñon--juniper woodland, Rocky Mountain ponderosa pine (Pinus ponderosa P.& C. Lawson var. scopulorum), and southern Rocky Mountain juniper woodland and savanna). The overall accuracy of the model was >82%. Our most conservative model predicted that 14.4% of the four-corners region represented a high risk of peridomestic exposure to Y. pestis.

A North American Yersinia pestis draft genome sequence: SNPs and phylogenetic analysis

Background

Yersinia pestis, the causative agent of plague, is responsible for some of the greatest epidemic scourges of mankind. It is widespread in the western United States, although it has only been present there for just over 100 years. As a result, there has been very little time for diversity to accumulate in this region. Much of the diversity that has been detected among North American isolates is at loci that mutate too quickly to accurately reconstruct large-scale phylogenetic patterns. Slowly-evolving but stable markers such as SNPs could be useful for this purpose, but are difficult to identify due to the monomorphic nature of North American isolates.

Methodology/Principal Findings

To identify SNPs that are polymorphic among North American populations of Y. pestis, a gapped genome sequence of Y. pestis strain FV-1 was generated. Sequence comparison of FV-1 with another North American strain, CO92, identified 19 new SNP loci that differ among North American isolates.

Conclusions/Significance

The 19 SNP loci identified in this study should facilitate additional studies of the genetic population structure of Y. pestis across North America.

Introduction: conceptualizing and partitioning the emergence process of zoonotic viruses from wildlife to humans

This introduction provides a telegraphic overview of the processes of zoonotic viral emergence, the intricacies of host-virus interactions, and the distinct role of biological transitions and modifying factors. The process of emergence is conceptualized as two transition stages which are common and required for all disease emergence, (1) human contact with the infectious agent and (2) cross-species transmission of the agent, and two transition stages which are not required for emergence and appear unavailable to many zoonotic pathogens, (3) sustained human-to-human transmission and (4) genetic adaptation to the human host. The latter two transitions are presumably prerequisites for the pandemic emergence of a pathogen. The themes introduced herein are amplified and explored in detail by the contributors to this volume. Each author explores the mechanisms and unique circumstances by which evolution, biology, history, and current context have contrived to drive the emergence of different zoonotic agents by a series of related events; although recognizable similarities exist among the events leading to emergence the details and circumstances are never repetitive.

Emergence and persistence of hantaviruses

Hantaviral diseases have been recognized for hundreds of years but, until 1976, they had not been associated with an infectious agent. When Lee and colleagues isolated what is now known as Hantaan virus, the techniques they introduced allowed further investigations into the etiology of the classical hantavirus disease, hemorrhagic fever with renal syndrome (HFRS), now known to be caused by any of multiple hantaviruses. The discovery of hantavirus pulmonary syndrome (HPS) in the New World, and that it also can be caused by any of multiple hantaviruses (family Bunyaviridae, genus Hantavirus), has opened an entire field of epidemiologic, virologic, molecular, behavioral, and ecologic studies of these viruses. There appears to be a single hantavirus-single rodent host association, such that understanding the idiosyncrasies of each rodent host species and the ecologic variables that affect them are recognized as critical if we are to reduce human risk for infection. This chapter summarizes what is known about hantaviruses with regard to history of these viruses, their taxonomy, recognized geographical distribution, ecologic factors impacting their maintenance and spread of hantaviruses, effect of rodent behavior on hantavirus transmission, influence of host factors on susceptibility to and transmission of hantaviruses, and transmission of hantaviruses from rodents to humans. In addition, we summarize all these complexities and provide suggestions for future research directions.

Developing global climate anomalies suggest potential disease risks for 2006-2007

Background

El Niño/Southern Oscillation (ENSO) related climate anomalies have been shown to have an impact on infectious disease outbreaks. The Climate Prediction Center of the National Oceanic and Atmospheric Administration (NOAA/CPC) has recently issued an unscheduled El Niño advisory, indicating that warmer than normal sea surface temperatures across the equatorial eastern Pacific may have pronounced impacts on global tropical precipitation patterns extending into the northern hemisphere particularly over North America. Building evidence of the links between ENSO driven climate anomalies and infectious diseases, particularly those transmitted by insects, can allow us to provide improved long range forecasts of an epidemic or epizootic. We describe developing climate anomalies that suggest potential disease risks using satellite generated data.

Results

Sea surface temperatures (SSTs) in the equatorial east Pacific ocean have anomalously increased significantly during July – October 2006 indicating the typical development of El Niño conditions. The persistence of these conditions will lead to extremes in global-scale climate anomalies as has been observed during similar conditions in the past. Positive Outgoing Longwave Radiation (OLR) anomalies, indicative of severe drought conditions, have been observed across all of Indonesia, Malaysia and most of the Philippines, which are usually the first areas to experience ENSO-related impacts. This dryness can be expected to continue, on average, for the remainder of 2006 continuing into the early part of 2007. During the period November 2006 – January 2007 climate forecasts indicate that there is a high probability for above normal rainfall in the central and eastern equatorial Pacific Islands, the Korean Peninsula, the U.S. Gulf Coast and Florida, northern South America and equatorial east Africa. Taking into consideration current observations and climate forecast information, indications are that the following regions are at increased risk for disease outbreaks: Indonesia, Malaysia, Thailand and most of the southeast Asia Islands for increased dengue fever transmission and increased respiratory illness; Coastal Peru, Ecuador, Venezuela, and Colombia for increased risk of malaria; Bangladesh and coastal India for elevated risk of cholera; East Africa for increased risk of a Rift Valley fever outbreak and elevated malaria; southwest USA for increased risk for hantavirus pulmonary syndrome and plague; southern California for increased West Nile virus transmission; and northeast Brazil for increased dengue fever and respiratory illness.

Conclusion

The current development of El Niño conditions has significant implications for global public health. Extremes in climate events with above normal rainfall and flooding in some regions and extended drought periods in other regions will occur. Forecasting disease is critical for timely and efficient planning of operational control programs. In this paper we describe developing global climate anomalies that suggest potential disease risks that will give decision makers additional tools to make rational judgments concerning implementation of disease prevention and mitigation strategies.

Epidemiological trends for human plague in Madagascar during the second half of the 20th century: a survey of 20 900 notified cases

OBJECTIVES

To describe the principal characteristics and epidemiological trends for human plague in modern times based on the largest reported series of cases from the highly active Malagasy focus.

METHODS

We used a file of 20,900 notified cases of suspected plague, 4,473 of which were confirmed or probable, to carry out a statistical analysis of incidence and mortality rates and associated factors for 5-year periods from 1957 to 2001.

RESULTS

Our analysis of trends showed (1) an increase in the incidence rate and the number of districts affected, (2) an increase in the proportion of bubonic forms (64.8-96.8%) at the expense of the pneumonic forms (35.2-3.2%) more frequent in elderly subjects and (3) a decrease in case fatality rate (CFR, 55.7-20.9%) associated with five factors: clinical form, season, province, urban/rural and period considered. The median age of patients was 14 years and more men than women were affected.

CONCLUSIONS

Since the end of the 1980s, the incidence of plague in Madagascar has increased in both rural and urban areas, because of multiple socioeconomic and environmental factors. However, the plague mortality rate has tended to decrease, together with the frequency of pneumonic forms, because of the strengthening of control measures. Making dipstick tests for the rapid diagnosis of human cases and epizootics in rats available for health structures should make it possible to raise the alarm and to react rapidly, thereby further decreasing morbidity and CFR.

Impact of regional climate change on human health

The World Health Organisation estimates that the warming and precipitation trends due to anthropogenic climate change of the past 30 years already claim over 150,000 lives annually. Many prevalent human diseases are linked to climate fluctuations, from cardiovascular mortality and respiratory illnesses due to heatwaves, to altered transmission of infectious diseases and malnutrition from crop failures. Uncertainty remains in attributing the expansion or resurgence of diseases to climate change, owing to lack of long-term, high-quality data sets as well as the large influence of socio-economic factors and changes in immunity and drug resistance. Here we review the growing evidence that climate-health relationships pose increasing health risks under future projections of climate change and that the warming trend over recent decades has already contributed to increased morbidity and mortality in many regions of the world. Potentially vulnerable regions include the temperate latitudes, which are projected to warm disproportionately, the regions around the Pacific and Indian oceans that are currently subjected to large rainfall variability due to the El Niño/Southern Oscillation sub-Saharan Africa and sprawling cities where the urban heat island effect could intensify extreme climatic events.

Natural history of plague: perspectives from more than a century of research

For more than a century, scientists have investigated the natural history of plague, a highly fatal disease caused by infection with the gram-negative bacterium Yersinia pestis. Among their most important discoveries were the zoonotic nature of the disease and that plague exists in natural cycles involving transmission between rodent hosts and flea vectors. Other significant findings include those on the evolution of Y. pestis; geographic variation among plague strains; the dynamics and maintenance of transmission cycles; mechanisms by which fleas transmit Y. pestis; resistance and susceptibility among plague hosts; the structure and typology of natural foci; and how landscape features influence the focality, maintenance, and spread of the disease. The knowledge gained from these studies is essential for the development of effective prevention and control strategies.

Differential plague-transmission dynamics determine Yersinia pestis population genetic structure on local, regional, and global scales

Plague, the disease caused by the bacterium Yersinia pestis, has greatly impacted human civilization. Y. pestis is a successful global pathogen, with active foci on all continents except Australia and Antarctica. Because the Y. pestis genome is highly monomorphic, previous attempts to characterize the population genetic structure within a single focus have been largely unsuccessful. Here we report that highly mutable marker loci allow determination of Y. pestis population genetic structure and tracking of transmission patterns at two spatial scales within a single focus. In addition, we found that in vitro mutation rates for these loci are similar to those observed in vivo, which allowed us to develop a mutation-rate-based model to examine transmission mechanisms. Our model suggests there are two primary components of plague ecology: a rapid expansion phase for population growth and dispersal followed by a slower persistence phase. This pattern seems consistent across local, regional, and even global scales.

El Niño and health

El Niño Southern Oscillation (ENSO) is a climate event that originates in the Pacific Ocean but has wide-ranging consequences for weather around the world, and is especially associated with droughts and floods. The irregular occurrence of El Niño and La Niña events has implications for public health. On a global scale, the human effect of natural disasters increases during El Niño. The effect of ENSO on cholera risk in Bangladesh, and malaria epidemics in parts of South Asia and South America has been well established. The strongest evidence for an association between ENSO and disease is provided by time-series analysis with data series that include more than one event. Evidence for ENSO's effect on other mosquito-borne and rodent-borne diseases is weaker than that for malaria and cholera. Health planners are used to dealing with spatial risk concepts but have little experience with temporal risk management. ENSO and seasonal climate forecasts might offer the opportunity to target scarce resources for epidemic control and disaster preparedness.

Spatial analysis of Yersinia pestis and Bartonella vinsonii subsp. berkhoffii seroprevalence in California coyotes (Canis latrans)

Zoonotic transmission of sylvatic plague caused by Yersinia pestis occurs in California, USA. Human infections with various Bartonella species have been reported recently. Coyotes (Canis latrans) are ubiquitous throughout California and can become infected with both bacterial agents, making the species useful for surveillance purposes. This study examined the geographic distribution of 863 coyotes tested for Y. pestis and Bartonella vinsonii subsp. berkhoffii serologic status to gain insight into the natural history of B. vinsonii subsp. berkhoffii and to characterize the spatial distribution of the two agents. We found 11.7% of specimens positive to Y. pestis and 35.5% positive to B. vinsonii subsp. berkhoffii. The two pathogens had distinct spatial clusters: Y. pestis was more prevalent in eastern portions of the state and B. vinsonii subsp. berkhoffii in coastal regions. Prevalence of Y. pestis increased with increasing elevation, whereas prevalence of B. vinsonii subsp. berkhoffii decreased with increasing elevation. There were differences in the proportions of positive animals on a yearly basis to both pathogens.

Satellite imagery characterizes local animal reservoir populations of Sin Nombre virus in the southwestern United States

The relationship between the risk of hantaviral pulmonary syndrome (HPS), as estimated from satellite imagery, and local rodent populations was examined. HPS risk, predicted before rodent sampling, was highly associated with the abundance of Peromyscus maniculatus, the reservoir of Sin Nombre virus (SNV). P. maniculatus were common in high-risk sites, and populations in high-risk areas were skewed toward adult males, the subclass most frequently infected with SNV. In the year after an El Niño Southern Oscillation (ENSO), captures of P. maniculatus increased only in high-risk areas. During 1998, few sites had infected mice, but by 1999, 1820 of the high-risk sites contained infected mice and the crude prevalence was 30.8%. Only 118 of the low-risk sites contained infected rodents, and the prevalence of infection was lower (8.3%). Satellite imagery identified environmental features associated with SNV transmission within its reservoir population, but at least 2 years of high-risk conditions were needed for SNV to reach high prevalence. Areas with persistently high-risk environmental conditions may serve as refugia for the survival of SNV in local mouse populations.

Climate variability and change in the United States: potential impacts on vector- and rodent-borne diseases

Diseases such as plague, typhus, malaria, yellow fever, and dengue fever, transmitted between humans by blood-feeding arthropods, were once common in the United States. Many of these diseases are no longer present, mainly because of changes in land use, agricultural methods, residential patterns, human behavior, and vector control. However, diseases that may be transmitted to humans from wild birds or mammals (zoonoses) continue to circulate in nature in many parts of the country. Most vector-borne diseases exhibit a distinct seasonal pattern, which clearly suggests that they are weather sensitive. Rainfall, temperature, and other weather variables affect in many ways both the vectors and the pathogens they transmit. For example, high temperatures can increase or reduce survival rate, depending on the vector, its behavior, ecology, and many other factors. Thus, the probability of transmission may or may not be increased by higher temperatures. The tremendous growth in international travel increases the risk of importation of vector-borne diseases, some of which can be transmitted locally under suitable circumstances at the right time of the year. But demographic and sociologic factors also play a critical role in determining disease incidence, and it is unlikely that these diseases will cause major epidemics in the United States if the public health infrastructure is maintained and improved.

Field trial of systemically delivered arthropod development-inhibitor (fluazuron) used to control woodrat fleas (Siphonaptera: Ceratophyllidae) and ticks (Acari: Ixodidae)

An orally delivered arthropod development-inhibitory (fluazuron) was evaluated for its potential to reduce the number of flea and tick vectors found on the dusky-footed woodrat Neotoma fuscipes Baird, a reservoir host important in disease enzootiology in northern California. Pigmented bait cubes containing fluazuron were distributed monthly to woodrat nests in a chaparral habitat for 1 yr. When compared with control woodrats, the numbers of fleas [primarily Orchopeas sexdentatus (Baker)] on treated woodrats were significantly reduced 3-4 mo after initial application, and remained so for the duration of the application period. By contrast, tick numbers were not significantly reduced on treated woodrats. After the cessation of treatments, flea indices remained lower on treated animals for up to 2 mo after application. Approximately 93% of woodrats captured in the treatment area excreted pigmented feces and 93% of distributed bait cubes were removed by woodrats, which indicates that the bait cube formulation and delivery system were highly effective. Bait cubes also were attractive to small rodents and ground-frequenting birds. The results of this study suggest that a monthly application program of fluazuron delivered by bait cube is effective in reducing woodrat flea-burdens, but is not effective, at least in the short-term, in controlling ticks.