Outbreaks In Human Populations Research Articles

CAN CULLING TO PREVENT MONKEYPOX INFECTION BE COUNTER-PRODUCTIVE? SCENARIOS FROM A THEORETICAL MODEL

In the last two decades, monkeypox outbreaks in human populations in Africa and North America have reminded us that smallpox is not the only poxvirus with potential to cause harm in human populations. Monkeypox transmission is sustained in animal reservoirs, and animal–human contacts are responsible for sporadic outbreaks in humans. Here, we develop and analyze a deterministic epizootic (animal-based) transmission model capturing disease dynamics in an animal population, disease dynamics in an age-structured human population, and their coupling through animal–human contacts. We develop a single-patch model as well as a two-patch meta-population extension. We derive mathematical expressions for the basic reproduction number, which governs the likelihood of a large outbreak. We also investigate the effectiveness of culling strategies and the impact of changes in the animal–human contact rate. Numerical analysis of the model suggests that, for some parameter values, culling can actually have the counter-productive outcome of increasing monkeypox infection in children, if animal reproduction is a density-dependent process. The likelihood of this happening, as well as the prevalence of monkeypox in humans, depends sensitively on the animal–human contact rate. We also find that ignoring age structure in human populations can lead to overestimating the transmissibility of monkeypox in humans. The effectiveness of monkeypox control strategies such as culling can strongly depend on the details of demography and epidemiology in the animal reservoirs that sustain it. Therefore, to better understand how to prevent and control monkeypox outbreaks in humans, better empirical data from wild animal populations where monkeypox is endemic must be collected, and these data must be incorporated into highly structured theoretical models.

Salmonella spp. and Escherichia coli: survival and growth in plant tissue

This review presents information on disease outbreaks in human populations linked to Salmonella spp. and Escherichia coli O157:H7 associated with the consumption of fresh produce. It focuses on the processes of bacterial internalization and survival in non-host plant tissues and the role of biofilms in bacterial persistence. Research to identify the microbial sources contaminating fruits and vegetables and their persistence is urgently required. Internalization of human pathogenic bacteria in plant tissues is reported for various fruits. Under certain circumstances these can enter the plant via roots or seeds, with subsequent survival and translocation within the plant. Research should continue on the relationships between human pathogens and plants, and treatments should be developed to minimize pathogen presence on the surface of raw produce and to prevent their internalization.

Predicting the Timing and Magnitude of Tropical Mosquito Population Peaks for Maximizing Control Efficiency

The transmission of mosquito-borne diseases is strongly linked to the abundance of the host vector. Identifying the environmental and biological precursors which herald the onset of peaks in mosquito abundance would give health and land-use managers the capacity to predict the timing and distribution of the most efficient and cost-effective mosquito control. We analysed a 15-year time series of monthly abundance of Aedes vigilax, a tropical mosquito species from northern Australia, to determine periodicity and drivers of population peaks (high-density outbreaks). Two sets of density-dependent models were used to examine the correlation between mosquito abundance peaks and the environmental drivers of peaks or troughs (low-density periods). The seasonal peaks of reproduction (r) and abundance () occur at the beginning of September and early November, respectively. The combination of low mosquito abundance and a low frequency of a high tide exceeding 7 m in the previous low-abundance (trough) period were the most parsimonious predictors of a peak's magnitude, with this model explaining over 50% of the deviance in . Model weights, estimated using AICc, were also relatively high for those including monthly maximum tide height, monthly accumulated tide height or total rainfall per month in the trough, with high values in the trough correlating negatively with the onset of a high-abundance peak. These findings illustrate that basic environmental monitoring data can be coupled with relatively simple density feedback models to predict the timing and magnitude of mosquito abundance peaks. Decision-makers can use these methods to determine optimal levels of control (i.e., least-cost measures yielding the largest decline in mosquito abundance) and so reduce the risk of disease outbreaks in human populations.

Antibody-dependent enhancement of Ebola virus infection.

Most strains of Ebola virus cause a rapidly fatal hemorrhagic disease in humans, yet there are still no biologic explanations that adequately account for the extreme virulence of these emerging pathogens. Here we show that Ebola Zaire virus infection in humans induces antibodies that enhance viral infectivity. Plasma or serum from convalescing patients enhanced the infection of primate kidney cells by the Zaire virus, and this enhancement was mediated by antibodies to the viral glycoprotein and by complement component C1q. Our results suggest a novel mechanism of antibody-dependent enhancement of Ebola virus infection, one that would account for the dire outcome of Ebola outbreaks in human populations.

Global awareness of disease outbreaks: the experience of ProMED-mail.

Public Health Reports / 2001 Supplement 2 / Volume 116 27 ProMED-mail was established to provide an early global warning of emerging diseases of humans, animals, and plants as well as of disease activities signaling biological warfare and bioterrorist activities. The creation of the ProMED-mail system filled a vacuum highlighted by the 1992 Institute of Medicine’s seminal publication of the occurrence of emerging diseases and reasons why we are likely to see increasing numbers of outbreaks in both developing and developed countries. ProMED-mail has electronically knitted together a global cadre of emerging disease specialists and other interested parties. It has been not inaccurately described as “the CNN of outbreaks.” Its first posting was on August 22, 1994 on “Sabia and Other Rodent-Borne Viruses.” In its five years, it has grown from 40 members to some 18,277 in 160 countries with an unrestricted membership, now more than 20,000 members. During 1999, 2,226 messages were posted, averaging more than six each day, seven days a week. The program has few graphics and loads quickly in locations with slow connection to the Internet; the search engine connects to prior posting, and other links are available. Veterinary activities play a significant role in monitoring emerging diseases because they are central to understanding new diseases in animal populations. New diseases in animals have an impact in and of themselves, but they can also serve as comparative lessons on disease ecology. Most strikingly, they can involve significant outbreaks in human populations as new zoonoses emerge and are characterized. Time and again, over the past five years, new diseases in humans can only be fully understood when the animal components have been delineated. In 1999, 63% of all postings were of animal diseases and infections; this is not an unusual percentage. In the few years that ProMED-mail has been functioning, one has noticed a significant change in the attitude of the medical fraternity to veterinarians. It was slow at first, but after two years there was a sudden shift as they seemed to become aware of the central position of veterinary medicine to human health, quite apart from food hygiene and the other Global Awareness of Disease Outbreaks: The Experience of ProMED-mail