The role of viral agents in aetiopathogenesis of acute rheumatic fever

T-Cell Receptor Sequences Identify Combined Coxsackievirus-Streptococci Infections as Triggers for Autoimmune Myocarditis and Coxsackievirus-Clostridia Infections for Type 1 Diabetes

Recent research suggests that T-cell receptor (TCR) sequences expanded during human immunodeficiency virus and SARS-CoV-2 infections unexpectedly mimic these viruses. The hypothesis tested here is that TCR sequences expanded in patients with type 1 diabetes mellitus (T1DM) and autoimmune myocarditis (AM) mimic the infectious triggers of these diseases. Indeed, TCR sequences mimicking coxsackieviruses, which are implicated as triggers of both diseases, are statistically significantly increased in both T1DM and AM patients. However, TCRs mimicking Clostridia antigens are significantly expanded in T1DM, whereas TCRs mimicking Streptococcal antigens are expanded in AM. Notably, Clostridia antigens mimic T1DM autoantigens, such as insulin and glutamic acid decarboxylase, whereas Streptococcal antigens mimic cardiac autoantigens, such as myosin and laminins. Thus, T1DM may be triggered by combined infections of coxsackieviruses with Clostridia bacteria, while AM may be triggered by coxsackieviruses with Streptococci. These TCR results are consistent with both epidemiological and clinical data and recent experimental studies of cross-reactivities of coxsackievirus, Clostridial, and Streptococcal antibodies with T1DM and AM antigens. These data provide the basis for developing novel animal models of AM and T1DM and may provide a generalizable method for revealing the etiologies of other autoimmune diseases. Theories to explain these results are explored.

Risk Factors for Acute Rheumatic Fever: Literature Review and Protocol for a Case-Control Study in New Zealand

Acute rheumatic fever (ARF) and its sequela, rheumatic heart disease (RHD), have largely disappeared from high-income countries. However, in New Zealand (NZ), rates remain unacceptably high in indigenous Māori and Pacific populations. The goal of this study is to identify potentially modifiable risk factors for ARF to support effective disease prevention policies and programmes. A case-control design is used. Cases are those meeting the standard NZ case-definition for ARF, recruited within four weeks of hospitalisation for a first episode of ARF, aged less than 20 years, and residing in the North Island of NZ. This study aims to recruit at least 120 cases and 360 controls matched by age, ethnicity, gender, deprivation, district, and time period. For data collection, a comprehensive pre-tested questionnaire focussed on exposures during the four weeks prior to illness or interview will be used. Linked data include previous hospitalisations, dental records, and school characteristics. Specimen collection includes a throat swab (Group A Streptococcus), a nasal swab (Staphylococcus aureus), blood (vitamin D, ferritin, DNA for genetic testing, immune-profiling), and head hair (nicotine). A major strength of this study is its comprehensive focus covering organism, host and environmental factors. Having closely matched controls enables the examination of a wide range of specific environmental risk factors.

Is susceptibility to chronic rheumatic heart disease determined in early infancy? An analysis of mortality in Britain during the 20th century

BACKGROUND

The reason why some individuals but not others are susceptible to rheumatic fever and chronic rheumatic heart disease is not understood. Because of the substantial evidence that poverty is an important determinant of the disease and must operate in early life, we have investigated the role of the early environment in an ecological study using 20(th) century mortality as an index of disease prevalence.

METHODS

We analysed 37,321 deaths from rheumatic heart disease in England and Wales during 1968-78. We compared the geographical distribution of deaths with previous infant mortality records from 1911 onwards. These records included details of mortality at different ages and from different causes. They also included data on housing and population density.

RESULTS

Mortality from rheumatic heart disease showed a strong correlation with past infant mortality that was consistently stronger with postneonatal mortality (deaths from one month to one year) than with neonatal mortality (deaths during the first month of life). Areas with high infant mortality from diarrhoea or bronchitis had the highest subsequent mortality from rheumatic heart disease. Although rheumatic heart disease was linked with early overcrowding, regression analyses suggested that overcrowding could not per se explain the infant mortality associations.

CONCLUSIONS

Chronic rheumatic heart disease may have its origins in early infancy. Our findings raise the possibility that susceptibility to rheumatic fever and rheumatic heart disease may be linked with infection in the postneonatal period. Alternatively, they may be explained by the operation of environmental factors that both predispose to infection in infancy and the subsequent liability to heart disease.

Unresolved issues in theories of autoimmune disease using myocarditis as a framework

Many theories of autoimmune disease have been proposed since the discovery that the immune system can attack the body. These theories include the hidden or cryptic antigen theory, modified antigen theory, T cell bypass, T cell-B cell mismatch, epitope spread or drift, the bystander effect, molecular mimicry, anti-idiotype theory, antigenic complementarity, and dual-affinity T cell receptors. We critically review these theories and relevant mathematical models as they apply to autoimmune myocarditis. All theories share the common assumption that autoimmune diseases are triggered by environmental factors such as infections or chemical exposure. Most, but not all, theories and mathematical models are unifactorial assuming single-agent causation of disease. Experimental and clinical evidence and mathematical models exist to support some aspects of most theories, but evidence/models that support one theory almost invariably supports other theories as well. More importantly, every theory (and every model) lacks the ability to account for some key autoimmune disease phenomena such as the fundamental roles of innate immunity, sex differences in disease susceptibility, the necessity for adjuvants in experimental animal models, and the often paradoxical effect of exposure timing and dose on disease induction. We argue that a more comprehensive and integrated theory of autoimmunity associated with new mathematical models is needed and suggest specific experimental and clinical tests for each major theory that might help to clarify how they relate to clinical disease and reveal how theories are related.

Cutting edge issues in rheumatic fever

Although the incidence of acute rheumatic fever and rheumatic heart disease has decreased significantly in regions of the world where antibiotics are easily accessible, there remains a high incidence in developing nations as well as in certain regions where there is a high incidence of genetic susceptibility. These diseases are a function of poverty, low socioeconomic status, and barriers to healthcare access, and it is in the developing world that a comprehensive prevention program is most critically needed. Development of group A streptococcal vaccines has been under investigation since the 1960s and 50 years later, we still have no vaccine. Factors that contribute to this lack of success include a potential risk for developing vaccine-induced rheumatic heart disease, as well as difficulties in covering the many serological subtypes of M protein, a virulence factor found on the surface of the bacterium. Yet, development of a successful vaccine program for prevention of group A streptococcal infection still offers the best chance for eradication of rheumatic fever in the twenty-first century. Other useful approaches include continuation of primary and secondary prevention with antibiotics and implementation of health care policies that provide patients with easy access to antibiotics. Improved living conditions and better hygiene are also critical to the prevention of the spread of group A streptococcus, especially in impoverished regions of the world. The purpose of this article is to discuss current and recent developments in the diagnosis, pathogenesis, and management of rheumatic fever and rheumatic heart disease.

The worldwide epidemiology of acute rheumatic fever and rheumatic heart disease

Acute rheumatic fever (ARF) and rheumatic heart disease (RHD) are significant public health concerns around the world. Despite decreasing incidence, there is still a significant disease burden, especially in developing nations. This review provides background on the history of ARF, its pathology and treatment, and the current reported worldwide incidence of ARF and prevalence of RHD.