As of 2010, about 100 countries have endemic malaria. Every year, 125 million international travellers visit these countries, and more than 30,000 contract the disease.The geographic distribution of malaria within large regions is complex, and malaria-afflicted and malaria-free areas are often found close to each other. Malaria is prevalent in tropical and subtropical regions because of rainfall, consistent high temperatures and high humidity, along with stagnant waters where mosquito larvae readily mature, providing them with the environment they need for continuous breeding. In drier areas, outbreaks of malaria have been predicted with reasonable accuracy by mapping rainfall. Malaria is more common in rural areas than in cities. For example, several cities in the Greater Mekong Subregion of Southeast Asia are essentially malaria-free, but the disease is prevalent in many rural regions, including along international borders and forest fringes. In contrast, malaria in Africa is present in both rural and urban areas, though the risk is lower in the larger cities.Since 1900 there has been substantial change in temperature and rainfall over Africa. However, factors that contribute to how rainfall results in water for mosquito breeding are complex, incorporating the extent to which it is absorbed into soil and vegetation for example, or rates of runoff and evaporation. Recent research has provided a more in-depth picture of conditions across Africa, combining a malaria climatic suitability model with a continental-scale model representing real-world hydrological processes.
It is theorized that CD8+ immune cells become overactive by stimulation from drugs or drug metabolites. CD8+ T cells then mediate keratinocyte cell death through release of a number of molecules, including perforin, granzyme B, and granulysin. Other agents, including tumor necrosis factor alpha and Fas ligand, also appear to be involved in TEN pathogenesis. Diagnosis
The diagnosis of TEN is based on both clinical and histologic findings. Early TEN can resemble non-specific drug reactions, so clinicians should maintain a high index of suspicion for TEN. The presence of oral, ocular, and/or genital mucositis is helpful diagnostically, as these findings are present in nearly all patients with TEN. The Nikolsky sign (a separation of the papillary dermis from the basal layer upon gentle lateral pressure) and the Asboe-Hansen sign (a lateral extension of bullae with pressure) are also helpful diagnostic signs found in patients with TEN.Given the significant morbidity and mortality from TEN, as well as improvement in outcome from prompt treatment, there is significant interest in the discovery of serum biomarkers for early diagnosis of TEN. Serum granulysin and serum high-mobility group protein B1 (HMGB1) are among a few of the markers being investigated which have shown promise in early research. Histology
Definitive diagnosis of TEN often requires biopsy confirmation. Histologically, early TEN shows scattered necrotic keratinocytes. In more advanced TEN, full thickness epidermal necrosis is visualized, with a subepidermal split, and scant inflammatory infiltrate in the papillary dermis. Epidermal necrosis found on histology is a sensitive but nonspecific finding for TEN.