The epidemiology of the arthropod-borne encephalitides must account for the maintenance and dissemination of the viruses in nature in the absence of humans. Viruses have been isolated from mosquitoes and ticks, which serve as reservoirs of infection. In ticks, the viruses may pass from generation to generation by the transovarian route, and in such instances, the tick acts as a true reservoir of the virus as well as its vector (see Figure 1). In tropical climates, where mosquito populations are present throughout the year, arboviruses cycle continually between mosquitoes and reservoir animals.

Fig1. Generalized transmission cycle of tick-borne flaviviruses, showing hosts for larval, nymphal, and adult ticks. Virus is passed to succeeding tick stages during molting (transstadial transmission), as well as transovarially to progeny of adult ticks. Both male and female ticks are involved in transmission. Tick borne encephalitis virus may be transmitted to uninfected ticks cofeeding on a vertebrate host without the requirement for active viremic infection of the host. (Adapted from Monath TP, Heinz FX: Flaviviruses. In Fields BN, Knipe DM, Howley PM [editors-in-chief]. Fields Virology, 3rd ed. Lippincott-Raven, 1996.)

In temperate climates, the virus may be reintroduced each year from the outside (eg, by birds migrating from tropical areas), or it may survive in the winter in the local area. Possible but unproved overwintering mechanisms include the following (see Figures 2 and 1): (1) Hibernating mosquitoes at the time of their emergence may reinfect birds; (2) the virus may remain latent in winter within bats, birds, mammals, or arthropods; and (3) cold-blooded vertebrates (snakes, turtles, lizards, alligators, frogs) may act as winter reservoirs.

Fig2. Generalized transmission cycle of mosquito-borne flaviviruses causing encephalitis. Summertime amplification and possible overwintering mechanisms are shown. Humans are dead-end hosts and do not contribute to perpetuation of virus transmission. Wild birds are the most common viremic hosts, but pigs play an important role in the case of Japanese encephalitis virus. The pattern shown applies to many (but not all) flaviviruses. (Adapted from Monath TP, Heinz FX: Flaviviruses. In Fields BN, Knipe DM, Howley PM [editors- in-chief]. Fields Virology, 3rd ed. Lippincott-Raven, 1996.)

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اخبار العتبة العباسية المقدسة

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مركز السيد جعفر الحلي يواصل تقديم خدماته الصحية للزائرين

العتبة العباسية المقدسة تحيي ذكرى هدم قبور أئمّة البقيع (عليهم السلام) في الصحن الشريف

تقديم المحاضرة السادسة من محفل نهج البلاغة الأسبوعي في بغداد

المزيد

الآخبار الصحية

اكتشاف هام قد يمهّد لعلاج جديد للسمنة

تغييرات بسيطة في نمط الحياة تقلل خطر أمراض القلب بنسبة كبيرة

ليس اللب فقط!.. قشرة وبذور المانغو تخفي فوائد صحية مذهلة

زيادة استهلاك الكالسيوم ومنتجات الألبان يحمينا من مشكلات صحية خطيرة

المزيد

الآخبار التكنلوجية

العلماء الروس يكتشفون طريقة تحسن فرص نجاح زراعة الأسنان

لحظة زمنية خاطفة في الدماغ تتحكم في التعلم والحركة

القمر لم يعد مجرد محطة.. خطوة جديدة تغيّر مستقبل البشرية

العلماء يكتشفون "نوعا جديد تماما" من الكواكب

المزيد

مواضيع ذات صلة

HIV Infections in Humans: Laboratory Diagnosis

HIV Infections in Humans :Clinical Findings

HIV Infections in Humans : Pathogenesis and Pathology

Animal Lentivirus Systems

Classification of Lentiviruses

Viral DNA Is Integrated into the Host-Cell Genome in Some Nonlytic Viral Growth Cycles

Lytic Viral Growth Cycles Lead to Death of Host Cells

Viral Capsids Are Regular Arrays of One or a Few Types of Protein

Structure and Composition of Lentiviruses

HERPESVIRUSES

POLYOMAVIRUSES

Human T-Lymphotropic Viruses