النتائج 1 إلى 2 من 2



الموضوع: Viral Infection

  1. #1
    تاريخ التسجيل
    May 2006
    الدولة
    palestine
    المشاركات
    426

    افتراضي Viral Infection

    Herpes Viruses
    • A large number of herpes viruses have been described.
    • At least 8 of these, the Human Herpes Viruses (HHVs), infect humans and can cause clinical disease (HHV1-8). Due to historical reasons, HHV1-HHV5 are also known by other names:
    HHV1Herpes Simplex Virus 1 (HSV1)HHV2Herpes Simplex Virus 2 (HSV2)HHV3Varicella Zoster Virus (VZV)HHV4Epstein Barr Virus (EBV)HHV5Cytomegalovirus (CMV)

    Importance to Dentistry
    • Six HHVs cause human diseases of relevance to the practice of dentistry (HHV1-5 & HHV8).
    • HHVs are well-adapted to their (human) host and infection rates are high in most populations.
    • As a dentist you will be expected to diagnose, initiate management and know when to appropriately refer for a specialist opinion, patients with HHV infections.
    • It is particularly important that appropriate Cross Infection control measures are employed to prevent unnecessary spread of HHV infections in the dental practice.

    Primary Infection, Latency & Reactivation
    • HHV infections have three phases: primary infection, latency and reactivation. Variation in each phase exist between the different HHVs, but there are shared features.
    Primary infection: During primary infection there is viral replication and the patient is infectious. In immunocompetent individuals primary infection is mostly either subclinical (asymptomatic) or causes a mild illness and only a small proportion of patients develop florid clinical illness. Primary infection is self-limiting in immunocompetent patients. By contrast, primary HHV infection in immunocompromised patients is associated with high morbidity and can be fatal.
    Latency: Each HHV enters a latent state as the primary infection resolves. It remains in specific cell types for life and cannot be eliminated by host defences (i.e. infection is lifelong). Latent infection may occur in a different cell type from that involved in the primary infection. In the latent state the HHV does not cause disease, there is no viral replication and the patient is not infectious.
    Reactivation: Reactivation from the latent state occurs periodically. It is associated with further viral replication and the patient becomes infectious once again. However, reactivation is mostly asymptomatic and it is not obvious whether a patient is in either a latent or reactivated state. This is of particular relevance to cross infection control. Some patients do experience symptomatic reactivation. In immunocompetent patients this is typically mild, whereas in the immunocompromised, reactivation can be severe and even fatal. The clinical disease associated with reactivation may be different from that seen with primary infection. Accordingly, a single HHV is able to cause more than one clinical illness. For example, VZV causes chickenpox (primary infection) and shingles (reactivation). Factors controlling reactivation are poorly understood.

    HHV Infections in the Immunocompromised Patient
    • In immune competent patients any clinical illness tends to be mild and self-limiting.
    • HHVs cause severe and atypical clinical illness in immunocompromised patients.
    • Patients may be immunocompromised for many different reasons, most of which are acquired rather than congenital. These include:
      • Iatrogenic - the consequence of prescribed drugs such as corticosteroids or other immunosuppressants.
      • Cancer - often associated with dysregulation of the immune system.
      • Infection - patients with T-cell immunodeficiency (e.g. AIDS) generally have more severe and persistent HHV infections.
    • It is also important to remember that the immune system changes through life:
      • Neonates have an immature immune system and are particularly susceptible to severe HHV primary infection that may be fatal.
      • Primary HHV infection in pregnancy can be severe
        • HHV infection of the developing fetus can cause severe congenital abnormalities associated with mortality and high morbidity.
        • Pregnant women are at increased risk of developing severe primary HHV infection that can be fatal.
      • The immune system becomes less efficient with increasing age.
        • In particular, T-lymphocyte immunity is less effective in old age.

    Classification of Human Herpes Viruses
    HHVs are classified into one of three groups that are of relevance to understanding of the pathogenesis of HHV infections:
    Alpha-herpes viruses
    · HSV1, HSV2 & VZV.
    · Replicate rapidly in many different cell types, but especially stratified squamous epithelium.
    · Latent in nerve cells (neurotrophic) where they are unable to replicate.
    Beta-herpes viruses
    · CMV, HHV6 & HHV7.
    · Replicate slowly - infected cells typically become large.
    Gamma-herpes viruses
    · EBV & HHV8.
    · Replicate slowly - infection often associated with lymphocytes (lymphotrophic).
    · Able to induce cell-proliferation, which may be neoplastic (e.g. EBV & lymphomas).


    Terminology
    • 'Herpes' means 'to creep' and reflects how HHV infections spread from an infected cell to adjacent healthy cells which then become infected themselves.
    • 'Herpetic aphthous ulceration' is NOT related to HHV infection, but identifies a specific form of aphthous ulceration for which the cause if unknown. Unfortunately, this confusing terminology has become embedded in the literature.


  2. #2
    تاريخ التسجيل
    May 2006
    الدولة
    palestine
    المشاركات
    426

    افتراضي

    كنت عامل موضوع عنه على الpower Point مع صور
    بس ما عرفت كيف انزله
    يلا مش مشكله انشالله هاد يعجبكم
    شكرا


ضوابط المشاركة

  • لا تستطيع إضافة مواضيع جديدة
  • لا تستطيع الرد على المواضيع
  • لا تستطيع إرفاق ملفات
  • لا تستطيع تعديل مشاركاتك
  •