Some observations on the current plague outbreak in the Republic of Vietnam

Climate-driven marmot-plague dynamics in Mongolia and China

The incidence of plague has rebounded in the Americas, Asia, and Africa alongside rapid globalization and climate change. Previous studies have shown local climate to have significant nonlinear effects on plague dynamics among rodent communities. We analyzed an 18-year database of plague, spanning 1998 to 2015, in the foci of Mongolia and China to trace the associations between marmot plague and climate factors. Our results suggested a density-dependent effect of precipitation and a geographic location-dependent effect of temperature on marmot plague. That is, a significantly positive relationship was evident between risk of plague and precipitation only when the marmot density exceeded a certain threshold. The geographical heterogeneity of the temperature effect and the contrasting slopes of influence for the Qinghai-Tibet Plateau (QTP) and other regions in the study (nQTP) were primarily related to diversity of climate and landscape types.

Plague in Egypt: Disease biology, history and contemporary analysis: A minireview

Plague is a zoonotic disease with a high mortality rate in humans. Unfortunately, it is still endemic in some parts of the world. Also, natural foci of the disease are still found in some countries. Thus, there may be a risk of global plague re-emergence. This work reviews plague biology, history of major outbreaks, and threats of disease re-emergence in Egypt. Based on the suspected presence of potential natural foci in the country, the global climate change, and the threat posed by some neighbouring countries disease re-emergence in Egypt should not be excluded. The country is in need for implementation of some preventive measures.

Identification of Chinese plague foci from long-term epidemiological data

Carrying out statistical analysis over an extensive dataset of human plague reports in Chinese villages from 1772 to 1964, we identified plague endemic territories in China (i.e., plague foci). Analyses rely on (i) a clustering method that groups time series based on their time-frequency resemblances and (ii) an ecological niche model that helps identify plague suitable territories characterized by value ranges for a set of predefined environmental variables. Results from both statistical tools indicate the existence of two disconnected plague territories corresponding to Northern and Southern China. Altogether, at least four well defined independent foci are identified. Their contours compare favorably with field observations. Potential and limitations of inferring plague foci and dynamics using epidemiological data is discussed.

Climate predictors of the spatial distribution of human plague cases in the West Nile region of Uganda

East Africa has been identified as a region where vector-borne and zoonotic diseases are most likely to emerge or re-emerge and where morbidity and mortality from these diseases is significant. Understanding when and where humans are most likely to be exposed to vector-borne and zoonotic disease agents in this region can aid in targeting limited prevention and control resources. Often, spatial and temporal distributions of vectors and vector-borne disease agents are predictable based on climatic variables. However, because of coarse meteorological observation networks, appropriately scaled and accurate climate data are often lacking for Africa. Here, we use a recently developed 10-year gridded meteorological dataset from the Advanced Weather Research and Forecasting Model to identify climatic variables predictive of the spatial distribution of human plague cases in the West Nile region of Uganda. Our logistic regression model revealed that within high elevation sites (above 1,300 m), plague risk was positively associated with rainfall during the months of February, October, and November and negatively associated with rainfall during the month of June. These findings suggest that areas that receive increased but not continuous rainfall provide ecologically conducive conditions for Yersinia pestis transmission in this region. This study serves as a foundation for similar modeling efforts of other vector-borne and zoonotic disease in regions with sparse observational meteorologic networks.

Plague and climate: scales matter

Plague is enzootic in wildlife populations of small mammals in central and eastern Asia, Africa, South and North America, and has been recognized recently as a reemerging threat to humans. Its causative agent Yersinia pestis relies on wild rodent hosts and flea vectors for its maintenance in nature. Climate influences all three components (i.e., bacteria, vectors, and hosts) of the plague system and is a likely factor to explain some of plague's variability from small and regional to large scales. Here, we review effects of climate variables on plague hosts and vectors from individual or population scales to studies on the whole plague system at a large scale. Upscaled versions of small-scale processes are often invoked to explain plague variability in time and space at larger scales, presumably because similar scale-independent mechanisms underlie these relationships. This linearity assumption is discussed in the light of recent research that suggests some of its limitations.

Correlates of environmental factors and human plague: an ecological study in Vietnam

BACKGROUND

Human plague caused by Yersinia pestis remains a public health threat in endemic countries, because the disease is associated with increased risk of mortality and severe economic and social consequences. During the past 10 years, outbreaks of plague have occasionally occurred in Vietnam's Central Highlands region. The present study sought to describe and analyse the occurrence of plague and its association with ecological factors.

METHODS

The study included all 510 communes of the Central Highlands region (with a total population of approximately 4 million) where 95% of incidence of plague cases in Vietnam had been reported from 1997 through 2002. Plague was clinically ascertained by using a standard protocol by WHO. Data on domestic fleas and rodents were obtained by using traps and periodic surveillance in accordance with the WHO guidelines. Temperature, duration of sunshine, rainfall and humidity were recorded as monthly averages by local meteorological stations. The association between these ecological factors and plague was assessed by using the Poisson regression model.

RESULTS

From 1997 through 2002, 472 cases of plague were reported, of whom 24 (5.1%) died. The incidence of plague peaked during the dry season, with approximately 63% of cases occurring from February through April. The risk of plague occurrence was associated with an increased monthly flea index (RR and 95% CI: 1.93; 1.61-2.33 for months with the flea index >1) and increased rodent density (RR 1.23; 1.15-1.32 per each 3% increase in density). Moreover, the risk of plague increased during the dry season (RR 2.07; 1.64-2.62), when rainfall fell <10 mm (RR 1.44; 1.17-1.77).

CONCLUSIONS

These data suggest that the flea index, rodent density and rainfall could be used as ecological indicators of plague risk in Vietnam. The data also suggest that the occurrence of plague in Vietnam's Central Highlands is likely resulted from multiple causes that remain to be delineated.

Immunization against potential biological warfare agents

The intentional release of biological agents by belligerents or terrorists is a possibility that has recently attracted increased attention. Law enforcement agencies, military planners, public health officials, and clinicians are gaining an increasing awareness of this potential threat. From a military perspective, an important component of the protective pre-exposure armamentarium against this threat is immunization. In addition, certain vaccines are an accepted component of postexposure prophylaxis against potential bioterrorist threat agents. These vaccines might, therefore, be used to respond to a terrorist attack against civilians. We review the development of vaccines against 10 of the most credible biological threats.

[Flea fauna of rodents in coastal region of Korea Addendum:Insecticide susceptibility test of Xenopsylla cheopis]

A survey on rats and rat-fleas was performed in costal area of Korea during 1972; Inchon, Kunsan, Yosu, Busan and other areas. The number of the caught rats was 1,448. Total number of collected fleas was 2,480. Geographical distribution were described. Flea index was in 1.71 total. Mothly flea indices were 0.35-0.84 in January to March, 2.13-2.59 in April to June, 0.58 in July and 1.82-4.91 in August to November. Mortality rate of X. cheopsis to various concentration of DDT in 1 hour exposure were 43.8 % in 4.0 %, 30.4 % in 1.0 %. In 24 hours exposure, the mortalities were 100 % in 4.0 %, 91.5 % in 2.0 %, 73.5 % in 1.0 % and 37.0 % in 0.5 % DDT.

Effectiveness of live or killed plague vaccines in man

While the safety of the available live plague vaccine EV 76 (Paris) continues to be the subject of further study, the USP formol-killed, virulent Pasteurella pestis (Yersinia pestis) suspension capable of protecting 60% of non-human primates, particularly Hanuman langurs (Presbytis entellus), warrants further clinical tests and field trials. Inoculated in a dosage of 2x10(9) killed plague bacilli (1 ml), followed by a booster of 400 million organisms (0.2 ml) in 1-3 months, this vaccine stimulates the appearance of passive mouse-protection antibodies (below an index of 10) and passive haemagglutinins in 60%-65% of human subjects. Recent experiences in Viet-Nam demonstrate that personnel vaccinated with the USP vaccine, although frequently exposed, enjoy almost complete freedom from the disease. One of the 4 known and confirmed cases of bubonic plague in North Americans occurred in an unvaccinated individual. Among individuals inoculated with the USP vaccine, 2 confirmed cases of pneumonic plague and 1 case of asymptomatic pharyngeal plague have been recorded. The incidence of plague in the Republic of Viet-Nam during the past 3 years is estimated at 13 263 cases in a population in part vaccinated with a live plague which exhibited inadequate immunogenic efficacy in experimental tests.

The impact of insecticide-resistance on control of vectors and vector-borne diseases

A questionnaire inquiring into the nature of schemes for the insecticidal control of disease vectors, the development of resistance in these vectors, and the effect of any such resistance on their control and on the extent of disease was sent to more than 100 health authorities throughout the world. The replies to the questionnaire are summarized in this paper.Until recently, the use of insecticides in public health has been largely based on three organochlorine compounds-DDT, HCH and dieldrin. However, in some countries resistance to these has now severely affected control both of many insect species and of the diseases they transmit (e.g., malaria, yellow fever, filariasis, typhus, plague). Certain other public health problems (onchocerciasis, Chagas' disease, trypanosomiasis, leishmaniasis) have not so far been greatly affected by resistance, but it is difficult to be sure of the continued reliability of the organochlorines.Research in the past 5 years, much of it sponsored by WHO, has shown the value of various organophosphorus and carbamate insecticides as replacements for the organochlorines, although resistance to them, too, can occur. Attention must therefore be focused on all facets of the use of these newer compounds and particular scrutiny made of possible instances of resistance to them.