The epidemiology of severe Streptococcus pyogenes disease in Europe

Diseases caused by the Lancefield group A streptococcus, Streptococcus pyogenes, are amongst the most challenging to clinicians and public health specialists alike. Although severe infections caused by S. pyogenes are relatively uncommon, affecting around 3 per 100,000 of the population per annum in developed countries, the case fatality is high relative to many other infections. Despite a long scientific tradition of studying their occurrence and characteristics, many aspects of their epidemiology remain poorly understood, and potential control measures undefined. Epidemiological studies can play an important role in identifying host, pathogen and environmental factors associated with risk of disease, manifestation of particular syndromes or poor survival. This can be of value in targeting prevention activities, as well directing further basic research, potentially paving the way for the identification of novel therapeutic targets. The formation of a European network, Strep-EURO, provided an opportunity to explore epidemiological patterns across Europe. Funded by the Fifth Framework Programme of the European Commission s Directorate-General for Research (QLK2.CT.2002.01398), the Strep-EURO network was launched in September 2002. Twelve participants across eleven countries took part, led by the University of Lund in Sweden. Cases were defined as patients with S. pyogenes isolated from a normally sterile site, or non-sterile site in combination with clinical signs of streptococcal toxic shock syndrome (STSS). All participating countries undertook prospective enhanced surveillance between 1st January 2003 and 31st December 2004 to identify cases diagnosed during this period. A standardised surveillance dataset was defined, comprising demographic, clinical and risk factor information collected through a questionnaire. Isolates were collected by the national reference laboratories and characterised according to their M protein using conventional serological and emm gene typing. Descriptive statistics and multivariable analyses were undertaken to compare characteristics of cases between countries and identify factors associated with increased risk of death or development of STSS. Crude and age-adjusted rates of infection were calculated for each country where a catchment population could be defined. The project succeeded in establishing the first European surveillance network for severe S. pyogenes infections, with 5522 cases identified over the two years. Analysis of data gathered in the eleven countries yielded important new information on the epidemiology of severe S. pyogenes infections in Europe during the 2000s. Comprehensive epidemiological data on these infections were obtained for the first time from France, Greece and Romania. Incidence estimates identified a general north-south gradient, from high to low. Remarkably similar age-standardised rates were observed among the three Nordic participants, between 2.2 and 2.3 per 100,000 population. Rates in the UK were higher still, 2.9/100,000, elevated by an upsurge in drug injectors. Rates from these northern countries were reasonably close to those observed in the USA and Australia during this period. In contrast, rates of reports in the more central and southern countries (Czech Republic, Romania, Cyprus and Italy) were substantially lower, 0.3 to 1.5 per 100,000 population, a likely reflection of poorer uptake of microbiological diagnostic methods within these countries. Analysis of project data brought some new insights into risk factors for severe S. pyogenes infection, especially the importance of injecting drug users in the UK, with infections in this group fundamentally reshaping the epidemiology of these infections during this period. Several novel findings arose through this work, including the high degree of congruence in seasonal patterns between countries and the seasonal changes in case fatality rates. Elderly patients, those with compromised immune systems, those who developed STSS and those infected with an emm/M78, emm/M5, emm/M3 or emm/M1 were found to be most likely to die as a result of their infection, whereas those diagnosed with cellulitis, septic arthritis, puerperal sepsis or with non-focal infection were associated with low risk of death, as were infections occurring during October. Analysis of augmented data from the UK found use of NSAIDs to be significantly associated with development of STSS, adding further fuel to the debate surrounding the role of NSAIDs in the development of severe disease. As a largely community-acquired infection, occurring sporadically and diffusely throughout the population, opportunities for control of severe infections caused by S. pyogenes remain limited, primarily involving contact chemoprophylaxis where clusters arise. Analysis of UK Strep-EURO data were used to quantify the risk to household contacts of cases, forming the basis of national guidance on the management of infection. Vaccines currently under development could offer a more effective control programme in future. Surveillance of invasive infections caused by S. pyogenes is of considerable public health importance as a means of identifying long and short-term trends in incidence, allowing the need for, or impact of, public health measures to be evaluated. As a dynamic pathogen co-existing among a dynamic population, new opportunities for exploitation of its human host are likely to arise periodically, and as such continued monitoring remains essential.

CADASIL: molecular studies on the most common hereditary vascular dementing disorder

Cerebral Autosomal Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy (CADASIL) is the most common hereditary vascular dementia. CADASIL is a systemic disease of small and medium-sized arteries although the symptoms are almost exclusively neurological, including migraineous headache, recurrent ischemic episodes, cognitive impairment and, finally, subcortical dementia. CADASIL is caused by over 170 different mutations in the NOTCH3 gene, which encodes a receptor expressed in adults predominantly in the vascular smooth muscle cells. The function of NOTCH3 is not crucial for embryonic development but is needed after birth. NOTCH3 directs postnatal arterial maturation and helps to maintain arterial integrity. It is involved in regulation of vascular tone and in the wound healing of a vascular injury. In addition, NOTCH3 promotes cell survival by inducing expression of anti-apoptotic proteins. NOTCH3 is a membrane-spanning protein with a large extracellular domain (N3ECD) containing 34 epidermal growth factor-like (EGF) repeats and a smaller intracellular domain with six ankyrin repeats. All CADASIL mutations are located in the EGF repeats and the majority of the mutations cause gain or loss of one cysteine residue in one of these repeats leading to an odd number of cysteine residues, which in turn leads to misfolding of N3ECD. This misfolding most likely alters the maturation, targetting, degradation and/or function of the NOTCH3 receptor. CADASIL mutations do not seem to affect the canonical NOTCH3 signalling pathway. The main pathological findings are the accumulation of the NOTCH3 extracellular domain on degenerating vascular smooth muscle cells (VSMCs), accumulation of granular osmiophilic material (GOM) in the close vicinity of VSMCs as well as fibrosis and thickening of arterial walls. Narrowing of the arterial lumen and local thrombosis cause insufficient blood flow, mainly in small arteries of the cerebral white matter, resulting in tissue damage and lacunar infarcts. CADASIL is suspected in patients with a suggestive family history and clinical picture as well as characteristic white matter alterations in magnetic resonance imaging. A definitive verification of the diagnosis can be achieved by identifying a pathogenic mutation in the NOTCH3 gene or through the detection of GOM by electron microscopy. To understand the pathology underlying CADASIL, we have generated a unique set of cultured vascular smooth muscle cell (VSMC) lines from umbilical cord, placental, systemic and cerebral arteries of CADASIL patients and controls. Analyses of these VSMCs suggest that mutated NOTCH3 is misfolded, thus causing endoplasmic reticulum stress, activation of the unfolded protein response and increased production of reactive oxygen species. In addition, mutation in NOTCH3 causes alterations in actin cytoskeletal structures and protein expression, increased branching and abnormal node formation. These changes correlate with NOTCH3 expression levels within different VSMCs lines, suggesting that the phenotypic differences of SMCs may affect the vulnerability of the VSMCs and, therefore, the pathogenic impact of mutated NOTCH3 appears to vary in the arteries of different locations. Furthermore, we identified PDGFR- as an immediate downstream target gene of NOTCH3 signalling. Activation of NOTCH induces up-regulation of the PDGFR- expression in control VSMCs, whereas this up-regulation is impaired in CADASIL VSMCs and might thus serve as an alternative molecular mechanism that contributes to CADASIL pathology. In addition, we have established the congruence between NOTCH3 mutations and electron microscopic detection of GOM with a view to constructing a strategy for CADASIL diagnostics. In cases where the genetic analysis is not available or the mutation is difficult to identify, a skin biopsy is an easy-to-perform and highly reliable diagnostic method. Importantly, it is invaluable in setting guidelines concerning how far one should proceed with the genetic analyses.