Identifying the Age Cohort Responsible for Transmission in a Natural Outbreak of Bordetella bronchiseptica

Identifying the major routes of disease transmission and reservoirs of infection are needed to increase our understanding of disease dynamics and improve disease control. Despite this, transmission events are rarely observed directly. Here we had the unique opportunity to study natural transmission of Bordetella bronchiseptica – a directly transmitted respiratory pathogen with a wide mammalian host range, including sporadic infection of humans – within a commercial rabbitry to evaluate the relative effects of sex and age on the transmission dynamics therein. We did this by developing an a priori set of hypotheses outlining how natural B. bronchiseptica infections may be transmitted between rabbits. We discriminated between these hypotheses by using force-of-infection estimates coupled with random effects binomial regression analysis of B. bronchiseptica age-prevalence data from within our rabbit population. Force-of-infection analysis allowed us to quantify the apparent prevalence of B. bronchiseptica while correcting for age structure. To determine whether transmission is largely within social groups (in this case litter), or from an external group, we used random-effect binomial regression to evaluate the importance of social mixing in disease spread. Between these two approaches our results support young weanlings – as opposed to, for example, breeder or maternal cohorts – as the age cohort primarily responsible for B. bronchiseptica transmission. Thus age-prevalence data, which is relatively easy to gather in clinical or agricultural settings, can be used to evaluate contact patterns and infer the likely age-cohort responsible for transmission of directly transmitted infections. These insights shed light on the dynamics of disease spread and allow an assessment to be made of the best methods for effective long-term disease control

Adenylate Cyclase Toxin Promotes Internalisation of Integrins and Raft Components and Decreases Macrophage Adhesion Capacity

Bordetella pertussis, the bacterium that causes whooping cough, secretes an adenylate cyclase toxin (ACT) that must be post-translationally palmitoylated in the bacterium cytosol to be active. The toxin targets phagocytes expressing the CD11b/CD18 integrin receptor. It delivers a catalytic adenylate cyclase domain into the target cell cytosol producing a rapid increase of intracellular cAMP concentration that suppresses bactericidal functions of the phagocyte. ACT also induces calcium fluxes into target cells. Biochemical, biophysical and cell biology approaches have been applied here to show evidence that ACT and integrin molecules, along with other raft components, are rapidly internalized by the macrophages in a toxin-induced calcium rise-dependent process. The toxin-triggered internalisation events occur through two different routes of entry, chlorpromazine-sensitive receptor-mediated endocytosis and clathrin-independent internalisation, maybe acting in parallel. ACT locates into raft-like domains, and is internalised, also in cells devoid of receptor. Altogether our results suggest that adenylate cyclase toxin, and maybe other homologous pathogenic toxins from the RTX (Repeats in Toxin) family to which ACT belongs, may be endowed with an intrinsic capacity to, directly and efficiently, insert into raft-like domains, promoting there its multiple activities. One direct consequence of the integrin removal from the cell surface of the macrophages is the hampering of their adhesion ability, a fundamental property in the immune response of the leukocytes that could be instrumental in the pathogenesis of Bordetella pertussis

Idiopathic hypertrophic pachymeningitis: an autoimmune IgG4-related disease

Hypertrophic pachymeningitis (HP) is a rare disorder that causes thickening of the dura mater. Inflammatory lesions may be located in the cerebral or spinal dura mater or, less frequently, in both locations simultaneously. Numerous clinico-pathological entities cause thickening of the pachymeninges. Indeed, HP is a potential manifestation of many different diseases, but the diagnosis often remains uncertain. Cases in which the pachymeningitis has no known aetiology are termed "idiopathic" HP (IHP). Recently, it has been suggested that IgG4-related disease represents a subset of cases previously diagnosed as idiopathic hypertrophic pachymeningitis. Little is known regarding the pathogenic events of IHP. In a general theory, the inflammatory infiltrate, mainly consisting of B and T lymphocytes, activates fibroblasts and induces collagen deposition, leading to tissue hypertrophy and increased dural thickness. Clinical manifestations of IHP depend upon the location of the inflammatory lesions and compression of the adjacent nervous structures. Three central pathological features are lymphoplasmacytic infiltration, obliterative phlebitis, and storiform fibrosis. MRI is the examination of choice for the preliminary diagnosis of IHP. Histopathological examination of a biopsy specimen of the dura mater would finally confirm the diagnosis. The differential diagnosis for HP is broad and includes infections, autoimmune disorders, and neoplasia. Currently, there is no consensus about treatment for patients with IHP. There is a preference for glucocorticoid treatment on diagnosis followed by the addition of other immunosuppressive agents in the event of a recurrence. Rituximab is used in patients who did not respond to glucocorticoids or to conventional steroid-sparing agents