Life Cycles and Reproduction

Varicella Zoster Virus is a virus completely unique to humans, therefore no other animal can host VZV and there is no animal equivalent. The virus is currently being studied by many biologist all over the world, but it is still unclear exactly what happens to the virus to make it go into latency and what triggers the virus to come out of latency. Because so little is known about the steps between latency and reactivation, it remains undetermined how exactly the life cycle of Varicella Zoster Virus works. There is an attempt to “recapitulate the full virus life cycle from primary infection to latency through to reactivation” according to M. Steain and his colleagues at the University of Sydney, though the attempts have not come through quite yet. M. Steain quotes “In order to elucidate the mechanisms which control the establishment of latency and reactivation as well as the effect of VZV replication on neuronal function, in vitro models of neuronal infection have been developed. Currently these models involve culturing and infecting dissociated human fetal neurons, with or without their supporting cells, an intact explant fetal dorsal root ganglia (DRG) model, neuroblastoma cell lines and rodent neuronal cell models. Each of these models has distinct advantages as well as disadvantages, and all have contributed towards our understanding of VZV neuronal infection”. What scientists do know is that the VZV operates the same way most viruses do, which is to attach to the host cells and reproduce with the injection and the multiplication of the viral chromosome.

An Average Virus Life Cycle

Relationship with Humans, Habitat and Circulation

The Varicella Zoster Virus (VZV) infects humans, usually within the first decade of life. When contracted during childhood, VZV comes in a mild form (Varicella)- if the VZV is contracted during adulthood (Herpes Zoster), it can be very severe. VZV is transmitted/ circulated in/through aerosol droplets or through direct contact with secretion or broken vesicle of an infected individual. These droplets are released from skin pox in infected people. Infected people are infectious from two days before the skin rash (small red bumps on the skin all over the body) and slight fever appear, until about a week post rash appearance. This means that he habitat of the virus is the human body and survives by being passed from human to human.

VZV is a latent virus, so an individual that is infected by VZV do not show symptoms until the VZV (which resides in the ganglia to reproduce) is reactivated. When reactivated, normally one to three weeks after the initial infection, a rash appears which consists of small, itchy, red lumps/ spots that appear on the abdomen.

There is a broad spectrum of similarities and differences between Varicella (chicken pox) and Herpes Zoster (shingles) which are both contracted through the Varicella Zoster Virus. For example, Varicella occurs in childhood and is spread by aerosols and Zoster occurs during adolescence or adulthood by recurrence of latent infections. Those with active Zoster may be contagious for those around the individual and those who come in contact may develop Varicella (chicken pox). Varicella mainly affects oropharynx and skin and Zoster affects the trigeminal, cervical, thoracic, or lumbosacral dermatome. However, Varicella and Zoster are both normally nonrecurring (no reactivation); in other words, once Varicella Zoster has run its course, infected bodies grow immune. There are always exceptions: Varicella may never be contracted and Zoster’s second attacks sometimes happen but are extremely rare.

Varicella, as mentioned earlier, is predominant in children. Fortunately, Varicella is not very dangerous; treatment includes only a 1% phenol calamine cream that will prevent itching that may scar. Zoster, contrary to above, is quite dangerous and can include many complications including severe post herpetic pain (painful condition involving nerve fibers and skin), ophthalmic Zoster (involving superficial and deep injuries to the eye) and Generalized Zoster (presence of vesicles distributed along dermatome with the normal rash). Zoster normally affects immune compromised patients and elderly people who what dwindling immune systems. There are always exceptions specific to patients. For example, the usually uneventful recovery from Varicella (chicken pox) is often much more dangerous in a child with leukemia, and may develop pneumonia.

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