Category Archives: Infectious Disease

All hail the new hepatitis C mouse model

With existing treatments only partially effective with major adverse effects and no vaccine currently available, hepatitis C virus (HCV) infection is a major health problem worldwide. An estimated 120 million people are chronically infected around the world and, therefore, at increased risk of liver damage (fibrosis and cirrhosis) and liver cancer. Research into potential new vaccines and therapies for HCV has been severely hampered by the lack of a small animal mouse model, often a crucial research tool to investigate disease progression and to test new drugs. Now, US scientists have for the first time made a genetically humanized mouse model for hepatitis C, which could prove vital in HCV infection research.
HCV is spread via blood-to-blood contact; anything from blood transfusions, sharing contaminated needles in injection drug use, and, as Pamela Anderson found out, contaminated tattoo needles. Diagnosis can be problematic and disease progression can be unpredictable, infected individuals range from being asymptomatic, to clearing the virus naturally or suffering progressive liver damage that, ultimately, leads to liver failure and need for transplantation.
Mice are normally resistant to HCV infection, only humans and chimpanzees are naturally permissive to HCV, and at least four human factors are critical for HCV entry, claudin 1, occuldin, CD81 and scavenger receptor type B class I (SCARBI). In their paper published this week in Nature, Marcus Dorner and colleagues built on existing knowledge that in vitro rodent cells only need to express occludin and CD81 to enable HCV entry. They reasoned that expressing these key human genes (CD81 and occludin) in mice could make living animals susceptible to HCV infection.
The scientists made mice that expressed human SCARB1, claudin 1, occludin and CD81 using an adenovirus as a vector to deliver the human genes into the mouse liver. Although mouse liver cells expressed these human genes (5% of cells expressed all four genes, whilst 18–25% expressed both CD81 and occludin), infecting these mice with HCV and proving they were infected was the major stumbling block as HCV infection in murine cells in vitro and in vivo is inefficient. Even though mice were infected with bioluminescent HCV (tagged with firefly luciferase), which can be easily detected if they replicated (the cells would ‘glow’), bioluminescent signals were not above background levels making it difficult to detect the virus. As an alternative approach, the mice were engineered to express the luciferase reporter whilst the HCV genome was engineered to express a protein that activates the bioluminesce reporter gene, such that delivery and replication of HCV in the liver leads to a bioluminescent signal. In this way, the researchers showed that all mice expressing at least human occludin and CD81 could indeed be infected with HCV. They then went on to validate their new model and demonstrated the in vivo role of SCARB1 in viral entry and uptake into host cells. Furthermore, the study authors managed to block HCV entry using passive immunisation (transfer of readymade anti-HCV antibodies) in the humanized mice. A promising HCV vaccine candidate (a recombinant vaccine virus vector expressing HCV proteins that has been shown to work in chimps) was also tested in the model mice and was shown to induce immunity and partial protection against HCV infection.
“To our knowledge, this is the first time that any step in the viral life cycle has been recapitulated in a rodent simply by the expression of human genes,” write the study authors. This new mouse model should enable scientists to closely study hepatitis C disease progression in a small animal model that is more amenable to lab research. Hopefully, new improved strategies (both drugs and vaccines) against HCV can be developed and used to guide any future clinical trials.

 

ResearchBlogging.orgDorner, M., Horwitz, J., Robbins, J., Barry, W., Feng, Q., Mu, K., Jones, C., Schoggins, J., Catanese, M., Burton, D., Law, M., Rice, C., & Ploss, A. (2011). A genetically humanized mouse model for hepatitis C virus infection Nature, 474 (7350), 208-211 DOI: 10.1038/nature10168

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Scale up diarrhoea prevention to save lives

A widespread scale up of existing low-cost and effective tools to prevent and treat diarrhoea could substantially reduce diarrhoeal deaths and could be a major step towards achieving the Millenium Development Goal 4 of reducing child mortality by 2015, according to research published in PLoS Medicine.

Depressingly, in this modern era, diarrhoea—three or more loose bowel movements a day—is still a common cause of death in developing countries and is the 2nd biggest killer of young children (under 5 years) worldwide. Poor hygiene, inadequate sanitation and lack of clean, safe drinking water all contribute to the spread of the harmful viruses, bacteria and parasites that cause diarrhoea. Now, Fischer Walker and colleagues use their Lives Saved Tool (LiST) to estimate the potential lives saved after implementing two different scale-up scenarios for key diarrhoeal prevention (breastfeeding, vitamin A supplements, basic water, sanitation, hygiene, and rotavirus vaccination) and treatment (oral rehydration salts, zinc supplementation, and antibiotics for dysentery) intervention strategies in 68 countries with high childhood mortality.

The researchers put forward two scenarios for the priority countries, which included Bangladesh, China and Haiti, for a 5-year period (between 2010 and 2015)—the “ambitious” (which assumed feasible improvement in all interventions) and the “universal” (which assumed near 100% coverage for all interventions). By 2015, diarrhoeal deaths could be reduced by 78% and 92% in the ambitious and universal scenarios, respectively. With the universal scenario, nearly 5 million deaths could be averted at an additional costs of US$0.80 per capita using some of the key diarrhoea prevention and treatment interventions (such as rotavirus vaccination and oral rehydration salts) and $3.24 per capita when all sanitation and water interventions (such as handwashing, improved sanitation and access to safe, clean water) implemented.

Fischer Walker and co-workers argue that “real progress” could be made in the treatment and management of diarrhoeal diseases if intervention strategies are made an international priority and the global health community works together to eliminate this harmful disease. Furthermore, the research acts as a pertinent reminder that we already have the technologies and interventions needed to prevent and reduce the devastating effects of diarrhoea, we just need to use them in the right scenario.

ResearchBlogging.orgWalker, C., Friberg, I., Binkin, N., Young, M., Walker, N., Fontaine, O., Weissman, E., Gupta, A., & Black, R. (2011). Scaling Up Diarrhea Prevention and Treatment Interventions: A Lives Saved Tool Analysis PLoS Medicine, 8 (3) DOI: 10.1371/journal.pmed.1000428

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Diagnosing schistosomiasis: urine-based tests better than traditional assays?

Taken from Wikipedia

Intestinal schistosomiasis (caused by the parasite Schistosoma mansoni) can be detected easily and accurately by measuring levels of an excreted parasite antigen called circulating cathodic antigen, or CCA, in an individual’s urine, according to new research published in PLoS Neglected Tropical Diseases. This method has been found to be at least as effective as the existing ‘gold standard’ diagnostic test the Kato-Katz assay—literally counting the number of parasite eggs per gram of poo—and also to blood tests that test for parasite-specific antibodies. Moreover, switching to these urine-based tests for schistomiasis diagnosis is, quite frankly, preferable to sifting through someone’s faeces (messy, risky, time consuming, and actually not that useful), and could also make it easier to assess the prevalence and resolution of S. mansoni infection, which could be beneficial for disease control programmes.

Taking advantage of a large study to assess schistosomiasis prevalence in young children, the researchers tested the sensitivity and specificity of two different types of CCA urine tests—a strip test designed for use in the laboratory (unfortunately no longer under production) and a cassette test suited for field use—and compared them to both the Kato-Katz technique for assessing S. mansoni egg burden and ELISAs to detect anti-schistosome antibodies. Stool, urine and blood samples were collected from 484 children (aged 1–15 years old) who lived in the village, Usoma, in Western Kenya, which is near Lake Victoria, an area known to have high S. mansoni infection rates. Even when taking into account the limitations of the Kato-Katz assay in their analysis, the urine-based diagnostics tests were still sensitive and specific with CCA test levels reflecting the stool egg burden, and thus the intensity of the infection (a finding that confirmed other study results). Moreover, the tests worked even if the children were also infected with other parasites (Ascaris lumbricoides, hookworm or Trichuris trichuria), which can affect the performance of some diagnostic tests.

The CCA diagnostic test for schistomiasis has now been shown to be effective in areas with a high burden of the disease, but more work is needed to see whether it is sensitive enough to detect disease in areas with low S. mansoni infection rates. Whether these urine tests will eventually replace the tried and tested Kato-Katz technique remains to be seen; one advantage of examining stool samples is that other parasites may be found and identified at the same time, which is not possible with the CCA test as it is specific for schistosomiasis.

ResearchBlogging.orgShane, H., Verani, J., Abudho, B., Montgomery, S., Blackstock, A., Mwinzi, P., Butler, S., Karanja, D., & Secor, W. (2011). Evaluation of Urine CCA Assays for Detection of Schistosoma mansoni Infection in Western Kenya PLoS Neglected Tropical Diseases, 5 (1) DOI: 10.1371/journal.pntd.0000951

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Spreading Salmonella—hyper-replicating bacteria act as a reservoir for dissemination

New research reveals how Salmonella enterica spread in the gut and gallbladder—a subpopulation of Salmonella primed for invasion rapidly replicate in the host cell cytosol such that bacteria-laden cells are extruded out of the epithelial-cell layer releasing invasive Salmonella into the gastrointestinal and biliary lumen. Leigh Knodler and colleagues write that other mucosal-dwelling pathogens could use this “host cell process as an exit strategy”.

Salmonella species can cause a range of infections from typhoid fever to food poisoning. Ordinarily, the intracellular bacteria Salmonella enterica resides and replicates within a membrane-bound vacuole in epithelial cells. During its life cycle, the bacteria are adapted to survive within a wide range of environmental niches within the human host (including cells such as enterocytes and macrophages and organs such as the spleen and gastrointestinal tract).

Knodler et al. observed a subpopulation of Salmonella that were ‘hyper-replicating’; these bacteria were doubling in number at almost five times the rate of the overall population of bacteria in the epithelial cell. Not only that, these bacteria were rapidly proliferating not in the Salmonella-containing vacuole, but in the host cell cytosol (which is believed to be nutrient rich) and were ready to invade other cells (they expressed type III secretion system 1 components and flagella, virulence factors that are required for invasion). Moreover, epithelial cells overloaded with these hyper-replicating cytosolic Salmonella were forced out of the apical side of the epithelial-cell layer—just as when dying cells are extruded out of the epithelium during the normal rapid turnover of epithelial cells that occurs to maintain the gut epithelium. Subsequently, invasive bacteria are released into the lumen and are primed and ready to infect new cells. The extruded host cells then die in a caspase-1-dependent manner and trigger the production of the proinflammatory cytokine interleukin 18—a process which could, in part, explain the high levels of mucosal inflammation observed in Salmonella infections of the gut and gallbladder.


ResearchBlogging.orgKnodler, L., Vallance, B., Celli, J., Winfree, S., Hansen, B., Montero, M., & Steele-Mortimer, O. (2010). Dissemination of invasive Salmonella via bacterial-induced extrusion of mucosal epithelia Proceedings of the National Academy of Sciences, 107 (41), 17733-17738 DOI: 10.1073/pnas.1006098107

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Monkeypox infections on the increase in Africa

The incidence of a smallpox-like disease—caused by the monkeypox virus—has increased 20-fold in the Demoncratic Republic of Congo (DRC) over the past 30 years, according to new research published online in the journal PNAS. The findings suggest that, as smallpox vaccination programmes ceased in the DRC in 1980, people are now immunologically ‘naïve’ to orthopoxviruses (including monkeypox and smallpox viruses) and could be at an increased risk of infection by this family of viruses.

The monkeypox virus can cause a serious zoonotic disease (potentially transmitted to humans from rodent species such as squirrels as well as primates such as monkeys) that is similar to smallpox. Smallpox vaccinations not only helped eradicate the smallpox virus, but also provided cross-protective immunity to monkeypox virus infection.

Anne Rimoin and colleagues assessed the burden of human monkeypox in the DRC by analyzing surveillance data for this disease from 2005–2007 in regions known to be endemic for the virus, a feat which had not been conducted since the early 1980s. In their up-to-date surveillance data across nine health zones in central DRC, 760 human monkeypox cases were confirmed by laboratory tests and the researchers found that the average annual cumulative incidence of monkeypox virus infection was 5.53 cases per 10,000 people across all zones. Men, children under the age of 15 years and people living in forested areas or who had not received a prior smallpox vaccination were at an increased risk of monkeypox infection whilst those who had been vaccinated against smallpox had a 5.2-fold lower risk of infection by the monkeypox virus than unvaccinated individuals. Rimoin et al. then compared the 1980s active surveillance data with their new 2000s findings from the same health zone and found that the incidence of human monkeypox in this zone increased substantially from 0.72 cases per 10,000 people in the 1980s to 14.42 cases per 10,000 people between 2005 and 2007.

The investigators add that “entire households are now mostly or completely [smallpox] vaccine naive”, which could result in increased human-human transmission between different generations within the same house. Furthermore, Rimoin and colleagues argue that because of several limitations (including poor access to remote areas) their study could have under-reported the true incidence of human monkeypox and the observed dramatic increase in disease incidence could in fact be a “conservative estimate”. Improved and continued disease surveillance will be needed to assess the true burden of monkeypox virus infection on public health in African populations, and could aid the development and implementation of strategies to reduce the risk of monkeypox virus infection.

ResearchBlogging.orgAnne W. Rimoin, Prime M. Mulembakani, Sara C. Johnston, James O. Lloyd Smith, Neville K. Kisalu, Timothee L. Kinkela, Seth Blumberg, Henri A. Thomassen, Brian L. Pike, Joseph N. Fair, Nathan D. Wolfe, Robert L. Shongo, Barney S. Graham, Pierre Formenty, E, & Major (2010). Major increase in human monkeypox incidence
30 years after smallpox vaccination campaigns
cease in the Democratic Republic of Congo Proceedings of the National Academy of Sciences USA (Published ahead of print 30th August 2010) DOI: 10.1073/pnas.1005769107

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Racial background affects risk of severe sepsis

High infection rates and increased risk of acute organ dysfunction in black individuals explains why people from this racial background are more likely to have (and die from) severe sepsis than white individuals, according to a new study published in JAMA.

Severe sepsis (when the body has a systemic inflammatory response to infection that can lead to multiple organ failure and death) is well-known to be more frequent in black individuals than white people. However, just why the incidence of severe sepsis is higher in this racial group is unknown and it is particularly important to investigate whether these racial disparities are because of different susceptibilities to infection or organ failure—a critical distinction that could influence treatment. High infection rates can be combated with vaccination programmes in at-risk individuals whilst high incidence rates of organ failure can be improved with better care in hospitals.

In what can only be described as a mammoth retrospective study (that included data from all hospitalisations across seven US states, that is, a potential total number of over 63 million people in the study), Florian B. Mayr and colleagues wanted to examine exactly why black people have a higher incidence of severe sepsis than white people.

The researchers found that of more than 8.6 million hospital admissions (not related to childbirth) in black and white individuals, over 2.2 million of the cases were because of infection and 381,787 of these cases (67,812 black patients; 313,975 white patients) had severe sepsis. They found that black patients had 67% higher hospitalization rates (after standardising for both age and sex) because of severe sepsis than did white patients. Furthermore, black patients also had both increased infection rates, risk of developing organ dysfunction and mortality compared with white patients. Differences in infection-related hospitalisations between the races were especially pronounced in younger adults (20–65 years old).

Findings from this large, retrospective cohort study clearly demonstrate that high severe sepsis rates in black people are because of a “higher likelihood of being hospitalised with infection and a higher risk of developing acute organ dysfunction”. These results have implications for public health; interventions to reduce infection (such as vaccinations) and better quality of care and management of hospitalised patients should be promoted, especially in healthcare providers that serve black communities. Furthermore, more research is needed to investigate risk of severe sepsis in people from other racial groups.

ResearchBlogging.orgMayr, F., Yende, S., Linde-Zwirble, W., Peck-Palmer, O., Barnato, A., Weissfeld, L., & Angus, D. (2010). Infection Rate and Acute Organ Dysfunction Risk as Explanations for Racial Differences in Severe Sepsis JAMA: The Journal of the American Medical Association, 303 (24), 2495-2503 DOI: 10.1001/jama.2010.851

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IL-33—a new treatment against sepsis?

New research shows that the novel cytokine interleukin (IL)-33 reduces sepsis and has “therapeutic potential” to treat this often fatal inflammatory condition. According to the study published this week in Nature Medicine, IL-33 promotes neutrophil recruitment to the site of infection, which is a critical host defence response, and the levels of the decoy IL-33 receptor soluble ST2 in serum could affect whether people recover from sepsis.

Sepsis is a serious illness in which the body has a massive inflammatory response to an infection. Severe sepsis and septic shock can affect multiple organs in the body including the heart, lungs, liver and brain, and is life-threatening (30–50% of people with severe sepsis or septic shock die) and requires treatment in intensive care.

Jose Alves-Filho and colleagues used experimental models of sepsis (using cecal ligation and puncture or CLP) to investigate the role of IL-33 during sepsis. The scientists induced sepsis in mice and then treated them with recombinant IL-33; IL-33-treated mice had a marked reduction in mortality compared to untreated controls and IL-33 protected mice from sepsis for 3h after CLP. The researchers found that IL-33 treatment increased the number of neutrophils migrating to the site of infection (by increasing the expression of the chemokine receptor that is crucial for neutrophil recruitment, CXCR2). This neutrophil recruitment promoted clearance of the bacterial infection and IL-33 also reduced the systemic proinflammatory cytokines (e.g. IL-6, tumour necrosis factor α and CXCL2) that occurred in response to the infective bacteria. Furthermore, the scientists analysed blood serum from healthy individuals and people who had sepsis. They found that people with sepsis had higher levels of IL-33 than healthy people, and that serum levels of soluble ST2 (the decoy receptor of IL-33) were substantially higher in people who did not survive sepsis compared to those who recovered from the disease (soluble ST2 serum levels were negligible in healthy individuals).

The research reveals a “previously unknown mechanism of action of IL-33” and further studies will show whether IL-33 could be used as a potentially novel therapy for sepsis.

ResearchBlogging.orgAlves-Filho, J., Sônego, F., Souto, F., Freitas, A., Verri, W., Auxiliadora-Martins, M., Basile-Filho, A., McKenzie, A., Xu, D., Cunha, F., & Liew, F. (2010). Interleukin-33 attenuates sepsis by enhancing neutrophil influx to the site of infection Nature Medicine DOI: 10.1038/nm.2156

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