32 research outputs found
Host Specialization and Dispersal in Avian Haemosporidians
In order to be able to understand the ecological and evolutionary processes involved in the emergence of infectious diseases, one needs to comprehend how parasites arrive at new geographical areas and how they manage to maintain viable populations and even expand their ranges. We discuss host specificity in avian haemosporidians and how encounter and compatibility filters affect the dispersal of avian haemosporidians, and how these filters affect avian haemosporidian assemblages at different spatial and evolutionary scales. There are at least three important barriers to the dispersal of avian haemosporidians: (i) geographic barriers, (ii) environmental barriers, and (iii) interspecies barriers. In this chapter, we discuss the factors involved in these barriers and their effects on the structure of avian haemosporidian assemblages. Host specificity plays an important role in parasite dispersal, and in the case of avian haemosporidians that are vector-borne parasites, it needs to be evaluated both at the vector and bird host levels. Understanding the effects of these factors on hostâvectorâparasite dynamics is important to unravel the dispersal and diversification mechanisms of avian haemosporidians. We end this chapter reviewing host specialization in avian haemosporidians of tropical regions, discussing the mechanisms involved in the dispersal and specialization of these parasites and point out important research gaps that need attention
Specific Neurologic Complications of Human Immunodeficiency Virus Type 1 (HIV-1) Infection in Children
Hydrocephalus as the Initial Presentationof a Spinal Cord Astrocytoma Associa ted with Leptomeningeal Spread
Leptomeningeal dissemination of pilocytic astrocytoma at diagnosis in childhood: two cases report Disseminação leptomenĂngea de astrocitoma pilocĂtico ao diagnĂłstico: relato de dois casos
Pilocytic astrocytoma (PA) is a benign tumor that rarely spread along the neuraxis. At the moment there are no more than five cases of leptomeningeal dissemination (LD) from PA at diagnosis described in the literature. Different patterns of presentation or recurrence may be noted: local recurrence, malignant transformation, multicentric disease or metastatic disease. LD and multicentric disease can be distinct pathological entities. We report two cases and analyse literature, emphasizing leptomeningeal spread at presentation. Hydrocephalus, biopsy and parcial ressection are likely to be favorable factors to the occurrence of LD. Otherwise, LD may be part of natural history of PA, as evidenced by its ocurrence in non-treated cases.<br>Astrocitoma pilocĂtico (AP) Ă© tumor benigno que raramente se dissemina ao longo do neuroeixo. AtĂ© o momento nĂŁo hĂĄ mais que cinco casos de AP que se tenham apresentado com disseminação leptomenĂngea (DL) descritos na literatura. Diferentes padrĂ”es de apresentação ou recorrĂȘncia podem ser observados: recorrĂȘncia local, transformação maligna, doença multicĂȘntrica ou doença metastĂĄtica. DL e doença multicĂȘntrica podem ser entidades diferentes. Relatamos dois casos e analisamos a literatura. Hidrocefalia, biĂłpsia e ressecção parcial sĂŁo provavelmente fatores predisponentes Ă DL. Por outro lado, DL pode ser parte da histĂłria natural de AP, como pode ser evidenciado pela sua ocorrĂȘncia em casos nĂŁo tratados