MicrobiologyBytes

Aedes aegypti is the urban vector of dengue viruses worldwide. While climate influences the geographical distribution of this mosquito species, other factors also determine the suitability of the physical environment for this mosquito. Importantly, the close association of Ae. aegypti with humans and the domestic environment allows this species to persist in regions that may otherwise be unsuitable based on climatic factors alone. This review highlights the need to incorporate the impact of the urban environment in attempts to model the potential distribution of Ae. aegypti and briefly discuss the potential for future technology to aid management and control of this widespread vector species.

The dengue vector Aedes aegypti: What comes next. Microbes Infect. Jan 20 2010. doi:10.1016/j.micinf.2009.12.011

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• Population movement a critical factor in dengue virus spread
• Dengue Virus
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• Pathogenic Flaviviruses

There is strong evidence to suggest that climate change has, and will continue to affect the occurrence, distribution and prevalence of livestock diseases in Great Britain (GB). This paper reviews how climate change could affect livestock diseases in GB. Factors influenced by climate change and that could affect livestock diseases include the molecular biology of the pathogen itself; vectors (if any); farming practice and land use; zoological and environmental factors; and the establishment of new microenvironments and microclimates. The interaction of these factors is an important consideration in forecasting how livestock diseases may be affected. Risk assessments should focus on looking for combinations of factors that may be directly affected by climate change, or that may be indirectly affected through changes in human activity, such as land use (e.g. deforestation), transport and movement of animals, intensity of livestock farming and habitat change. A risk assessment framework is proposed, based on modules that accommodate these factors. This framework could be used to screen for the emergence of unexpected disease events.

The effect of climate change on the occurrence and prevalence of livestock diseases in Great Britain: a review. J Appl Microbiol. (2009) 106(5): 1409-1423

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• Bluetongue virus
• MicrobiologyBytes: Climate Change

A soil bacterium protein used to kill insects on organic crops has been shown to be a highly effective treatment for intestinal parasitic roundworms. These parasites, which include hookworms and whipworms, infect about two billion people in underdeveloped tropical regions and are cumulatively one of the leading causes of debilitation worldwide. Scientists report that a crystal protein known as Cry5B produced by Bt (Bacillus thuringiensis) is highly effective at a single dose at curing mammals of intestinal roundworm infections.

The researchers showed that Bt crystal proteins, used as insecticides for over five decades and known to be non-toxic to vertebrates, kill roundworms. Parasitic roundworms are considered by public-health officials to have a combined debilitating impact on human populations that is comparable to, or in some estimates greater than, that of malaria or tuberculosis. Intestinal roundworm diseases are among the most important causes of disease burden in school-aged children worldwide, leading to stunted growth, retarded cognitive and mental development and malnutrition. Children with these parasites are more likely to be trapped in poverty because they cannot physically work or think their way out of their condition. The parasites also have a significant burden on pregnant women and working adults.

Despite the large impact of these parasites on the developing world, few drugs have been developed to effectively combat their infection in human populations. Only one drug, albendazole, is now widely used in administering single-dose treatments to large populations. But because of the enormous numbers of people that need to be treated repeatedly, the development of resistance to albendazole is a serious threat and is already suspected in three studies in Sri Lanka, Ethiopia and Uganda. Furthermore, albendazole is a far from ideal drug, having poor impact on whipworms and less than ideal incomplete impact on hookworms. The latest drug to be developed is tribendimidine, which clinically has similar efficacy as albendazole. But the Bt Cry5B protein is three times better than tribendimidine. Comparisons from the literature with the other anti-worm drugs against this same mouse parasite, Heligmosomoides bakeri, indicate that Cry5B is anywhere from 4 times to 10,000 times more effective than various other anti-worm drugs. Most of the Cry5B is degraded in the stomach, so if the protein can be protected from stomach degradation, it is likely to be an even more powerful drug against parasites. These results pave the way to developing Cry5B as a safe and superior drug against roundworms that can rid a terrible class of parasites from hundreds of millions of children and adults around the world.

Bacillus thuringiensis Cry5B Protein Is Highly Efficacious as a Single-Dose Therapy against an Intestinal Roundworm Infection in Mice. PLoS Negl Trop Dis 4(3): e614. doi:10.1371/journal.pntd.0000614

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Infectious diseases have for centuries ranked with wars and famine as major challenges to human progress and survival. They remain among the leading causes of death and disability worldwide. Against a constant background of established infections, epidemics of new and old infectious diseases periodically emerge, greatly magnifying the global burden of infections. Studies of these emerging infections reveal the evolutionary properties of pathogenic microorganisms and the dynamic relationships between microorganisms, their hosts and the environment.

Emerging infections (EIs) can be defined as “infections that have newly appeared in a population or have existed previously but are rapidly increasing in incidence or geographic range”. EIs have shaped the course of human history and have caused incalculable misery and death. In 1981, a new disease – acquired immune deficiency syndrome (AIDS) – was first recognized. As a global killer, AIDS now threatens to surpass the Black Death of the fourteenth century and the 1918–1920 influenza pandemic, each of which killed at least 50 million people. Of the newly emerging and re-emerging/resurging diseases that have followed the appearance of AIDS, some have been minor curiosities, such as the 2003 cases of monkeypox imported into the United States, whereas others, such as severe acute respiratory syndrome (SARS), which emerged in the same year, have had a worldwide impact. The 2001 anthrax bioterrorist attack in the United States falls into a third category: deliberately emerging diseases. EIs can be expected to remain a considerable challenge for the foreseeable future. Emergence results from dynamic interactions between rapidly evolving infectious agents and changes in the environment and in host behaviour that provide such agents with favourable new ecological niches. This review examines the nature and scope of emerging and re-emerging microbial threats and considers methods for their control.

The challenge of emerging and re-emerging infectious diseases. Nature 430, 242-249, 2004 doi:10.1038/nature02759

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• MicrobiologyBytes: Emerging Diseases

The first production from an oil well is the result of the pressure either of the pressure of earth’s overburden on the oil-bearing formation, or by pumping to create negative pressure. As this primary production declines, some oil wells are converted to injector wells, and either waterflooding or sometimes gas flooding are implemented. Even after this secondary production effort has reached its economic limit, two-thirds of the original oil in place is still left in the ground and tertiary measures may be employed. These include chemical enhanced oil recovery (EOR) methods such as polymer flooding, surfactant flooding, alkaline flooding, etc. or the use of thermal measures such as injection of steam or in situ combustion.

Another tertiary method of oil recovery is microbial enhanced oil recovery, commonly referred to as MEOR. There are several ways in which microorganisms can enhance oil recovery other than what is commonly referred to as MEOR. Microorganisms can be used to reduce the paraffin build-up in producing wells or they can be utilized to produce solvents or polymers above ground for pumping into the oil-bearing formation as in EOR. In reality, the difference between EOR and some of the MEOR methods is the means by which the recovery-enhancing chemicals are introduced into the reservoir. Normally however, MEOR refers to the use of microorganisms in the oil-bearing formation itself to enhance oil recovery.

Since 1946 more than 400 patents on MEOR have been issued, but none has gained acceptance by the oil industry. Most of the literature on MEOR is from laboratory experiments or from field trials of insufficient duration or that lack convincing proof of the process. Several authors have made recommendations required to establish MEOR as a viable method to enhance oil recovery, and until these tests are performed, MEOR will remain an unproven concept rather than a highly desirable reality.

Microbial enhanced oil recovery (MEOR). Curr Opin Microbiol. Feb 8 2010

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• New Microbial Fuels

Coldwater and tropical fish are the third most popular pet in the UK after cats and dogs. Over 3 million homeowners have a pond in their garden and many of these are stocked with fish, some of which, like koi carp, are very expensive. As Keith Way describes in this article in Microbiology Today (pdf) a whole host of viruses are in the environment just waiting to infect them with harmful diseases:

With the discovery of non-filterable disease agents, or viruses, in the late 19th century there came a greater realization of the role that viruses may play in infectious diseases of fish. However, the breakthrough for fish virology came with the general developments in virological techniques that blossomed in the 1950s and 60s. In particular, visualization of viruses by electron microscopy, improvements in protein and nucleic acid analysis and, most significantly, the isolation of viruses on continuous (immortal) fish cell lines. At the same time, aquaculture around the world developed in the 1960s and 70s, and farming of fish and fish-keeping rapidly increased. With these developments and, more recently, the global increase in trade in ornamental fish there has been an increase in new diseases and the emergence of serious virus diseases. Viruses that have caused serious but isolated disease outbreaks in cyprinid species and some ictalurid (catfish) species, and may affect coldwater ornamental fish, include aquareoviruses, coronaviruses, poxviruses and iridoviruses. More serious disease epidemics in ornamental species have been caused by rhabdoviruses and herpesviruses.

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Marine dinoflagellates produce a diverse suite of complex toxins, yet the biological reason remains unclear. Among this group, Karlodinium veneficum is a small (∼8–12 μm) phytoplankton, common in coastal aquatic ecosystems. It has a mixed nutritional mode, relying on both photosynthesis and phagotrophy for growth (mixotrophy). It is frequently present in relatively low cell abundance, but is capable of forming intense blooms that have been associated with fish kills. Karlotoxins (KmTxs), which are produced by K. veneficum, generate pores in membranes with sterols and increase the ionic permeability of cell membranes, resulting in membrane depolarization, disruption of motor functions, osmotic cell swelling, and lysis. These measured effects have been based on purified toxins. Karlotoxin type and cell amount vary with K. veneficum strain, culture conditions, and geographic location. Along the U.S. East Coast, K. veneficum strains from south of the Chesapeake Bay produce karlotoxin 2 (KmTx- 2), whereas those from within the Bay produce karlotoxin 1 (KmTx-1).

To date, the perceived ecological role for toxins has been relief from grazing pressures. New research suggests that karlotoxins also serve as a predation instrument. Using high-speed holographic microscopy, researchers measured the swimming behavior of several toxic and nontoxic strains of K. veneficum and their prey, Storeatula major, within dense suspensions. The selected strains produce toxins with varying potency and dosages, including a nontoxic one. Results clearly show that mixing the prey with the predatory, toxic strains causes prey immobilization at rates that are consistent with the karlotoxins’ potency and dosage. Even prey cells that continue swimming slow down after exposure to toxic predators. The swimming characteristics of predators vary substantially in pure suspensions, as quantified by their velocity, radii of helical trajectories, and direction of helical rotation. When mixed with prey, all toxic strains that are involved in predation slow down. Furthermore, they substantially reduced their predominantly vertical migration, presumably to remain in the vicinity of their prey. Conversely, the nontoxic control strain does not alter its swimming and does not affect prey behavior. In separate experiments, the authors show that exposing prey to exogenous toxins also causes prey immobilization at rates consistent with potency. Clearly, the toxic predatory strains use karlotoxins as a means of stunning their prey, before ingesting it. These findings add to our understanding of why some dinoflagellates produce such complex toxin molecules.

A dinoflagellate exploits toxins to immobilize prey prior to ingestion. PNAS USA January 19 2010. doi: 10.1073/pnas.0912254107

Historically, tuberculosis caused by Mycobacterium bovis (bovine tuberculosis, bTB) was a major public health issue in the UK. bTB in humans was widespread in the UK before the introduction of pasteurisation of milk in the 1960s: in the 1930s, 40% of dairy cows were infected and 0.5% had tuberculous mastitis. During this period, approximately 2500 people died annually from bTB. Therefore, measures were introduced to eliminate bTB from the UK. As a result, by the 1970s, bTB was eliminated from most of Britain, with persistent infection limited to the southwest. Subsequently, bTB has re-emerged: in 2007, there were 4172 new herd breakdowns in England and Wales. The resurgence of bTB has resulted in public expenditure now approaching £100 million annually. More and more extreme measures are being proposed to stop the spread of the disease such as widespread badger culling programmes, despite scientific studies casting doubt on the efficacy of such practices.

This article argues that, apart from milk pasteurisation, these measures no longer make economic sense and hence are now resulting in gross misallocation of public resources. We are therefore of the opinion that there is no public health rationale for the multimillion bTB control programme in the UK provided that milk continues to be pasteurised. The logical conclusion arising from this is that without a public health perspective, bTB is essentially an endemic animal disease and hence any control programme should be economically effective in terms of improvements in animal health and welfare and industry profitability or viability.

Public health and bovine tuberculosis: what’s all the fuss about? Trends in Microbiology, Nov 25 2009
Bovine tuberculosis (bTB) in UK cattle is increasing rapidly. Consequently, the UK Government is spending escalating sums of money in attempts at disease control. We propose that bTB control in cattle is irrelevant as a public health policy. In the UK, cattle-to-human transmission is negligible. Aerosol transmission, the only probable route of human acquisition, occurs at inconsequential levels when milk is pasteurised, even when bTB is highly endemic in cattle. Furthermore, there is little evidence for a positive cost benefit in terms of animal health of bTB control. Such evidence is required; otherwise, there is little justification for the large sums of public money spent on bTB control in the UK.

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• Origin and spread of Mycobacterium tuberculosis
• Tuberculosis – is the white plague winning?
• Irish badger cull ‘futile’ in controlling bovine tuberculosis
• Culling badgers a low priority for curbing cattle tuberculosis

Tropical coral reefs harbour a reservoir of enormous biodiversity that is increasingly threatened by direct human activities and indirect global climate shifts. Emerging coral diseases are one serious threat implicated in extensive reef deterioration through disruption of the integrity of the coral holobiont – a complex symbiosis between the coral animal, endobiotic alga and an array of microorganisms. In this article, the authors review the current understanding of the role of microorganisms in coral health and disease, and highlight the pressing interdisciplinary research priorities required to elucidate the mechanisms of disease. They advocate an approach that applies knowledge gained from experiences in human and veterinary medicine, integrated into multidisciplinary studies that investigate the interactions between host, agent and environment of a given coral disease. These approaches include robust and precise disease diagnosis, standardised ecological methods and application of rapidly developing DNA, RNA and protein technologies, alongside established histological, microbial ecology and ecological expertise. Such approaches will allow a better understanding of the causes of coral mortality and coral reef declines and help assess potential management options to mitigate their effects in the longer term.

The role of the environment in coral disease epizootics has been a major focus of investigations because coral reefs are the ecosystem facing the most rapidly advancing threat from climate change. Corals are sessile organisms and have the advantage that individual animals can be tracked in the wild to monitor disease progression. Significant challenges in framing the scale, complexity and natural variability of emerging coral diseases throughout the world’s oceans include a lack of historical baseline data sets and a wide diversity of ecological factors that influence disease patterns on both regional and global scales. Progress has been made to clarify the effects and drivers of coral disease on local and regional scales, and the field continues to refine the methods of coral disease assessment. However, developing a meaningful understanding of the interactions between the environment, the agent and the host is still required.

Microbial disease and the coral holobiont. Trends in Microbiology 17 (12) 554-562, 2009. doi:10.1016/j.tim.2009.09.004

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• White pox disease of coral