Viral infections causative viruses

Hepatitis is acute or chronic inflammation of the liver, which is frequently caused by infection with hepato-tropic viruses. Several forms of viral hepatitis (A, B, C, D, E) are known, which result from infection with viruses belonging to separate virus families, differing in their genomic organization, replication strategies, morphology and modes of transmission. 

HSV2 (herpes simplex virus 2), which causes significant morbidity and is an important cofactor for the transmission of HIV infection was recently targeted in a mouse model by local application of siRNA mixed with lipids. The results suggested that siRNA could work as active components of microbicides to prevent viral infection or transmission [2]. 

Before therapy is begun, culture and sensitivity tests (see Chap. 7) are performed to determine which antibiotic will best control the infection. These drug are of no value in the treatment of infections caused by a virus or fungus. There may be times when a secondary bacterial infection has occurred or potentially will occur when the patient has a fungal or viral infection. The primary health care provider may then order one of die... 

Although infections caused by a virus are common, antiviral drugp have limited use because they are effective against only a small number of specific viral infections. 

CMV, a virus of the herpes family, isa common viral infection. Healthy individuals may beoome infected yet have no symptoms. However, immunocompromised patients (such as those with HIV or cancer) may have the infection. Symptoms include malaise, fever, pneumonia, and super infection. Infants may acquire the virus from the mother while in the uterus, resulting in learning disabilities and mental retardation. CM V can infect the eye, causing retinitis. Symptoms of CMV retinitis are blurred vision and decreased visual acuity. Visual impairment is irreversible and can lead to blindness if untreated. 

Measles, mumps and rubella (German measles) are infectious diseases, with respiratory routes of transmission and infection, caused by members of the paramyxovirus group. Each virus is immunologically distinct and has only one serotype. Whilst the primary multiplication sites of these viruses is within the respiratory tract, the diseases are associated with viral multiplication elsewhere in the host. 

Catechins and proanthocyanidins have a documented antiviral activity. Catechins from an extract of Cocos nucifera husk fibre exhibited a strong inhibitory activity against acyclovir-resistant herpes simplex virus type 1 (HSV-l-ACVr) [62]. The use of 10 to 20ngml of ECG and EGCG has been reported to cause 50% inhibition of human immunodeficiency virus reverse transcriptase [89], while Kara and Nakayama [90] reported that a patented chewing gum containing tea catechins is claimed to prevent viral infections against influenza and to inhibit dissemination of this virus. 

Virus infection obviously upsets the regulatory mechanisms of the host, since there is a marked overproduction of nucleic acid and protein in the infected cell. In some cases, virus infection causes a complete shutdown of host macromolecular synthesis while in other cases host synthesis proceeds concurrently with virus synthesis. In either case, the regulation of virus synthesis is under the control of the virus rather than the host. There are several elements of this control which are similar to the host regulatory mechanisms, but there are also some uniquely viral regulatory mechanisms. We discuss various regulatory mechanisms when we consider the individual viruses later in this chapter. 

Viruses may also cause latent infection of a host. In a latent infection, there is a delay between infection by the virus and the appearance of symptoms. Fever blisters (cold sores), caused by the herpes simplex virus, result from a latent viral infection the symptoms reappear sporadically as the virus emerges from latency. The latent stage in viral infection of an animal cell is generally not due to the integration of the viral genome into the genome of the animal cell, as is the case with latent infections by temperate bacteriophages. 

A number of animal diseases caused by viruses involve primary demyelination and often are associated with inflammation. These diseases are studied as animal models, which may provide clues about how a viral infection could lead to immune-mediated demyelination in humans [1, 5, 6]. Canine distemper virus causes a demyelinating disease, and the lesions in dog brain show a strong inflammatory response with some similarities to acute disseminated encephalomyelitis in man [ 1 ]. Visna is a slowly progressive demyelinating disease of sheep caused by a retrovirus [ 1 ]. 

Despite the protective effect of NO against various viral infections, workers in several studies have shown a harmful role of NO in many systems. NO seems to play a part in the development of pneumonia caused by influenza virus [128], in the pathogenesis in mice of tick-borne encephalitis flavivirus infection [131], and in worsening the course of the murine myocarditis caused by coxsackievirus B3 [132]. In addition, pneumonia in mice induced by herpes simplex virus type 1 could be suppressed by the inhibitor of iNOS [133]. The issue of whether NO acts as an inhibitor of viral replication or as a harmful agent, therefore, remains unanswered. This issue is particularly evident in HIV-1 infection, since NO seems to act as a double-edged sword in the pathogenesis of HIV-1. 

Common viral infections may affect the outcome of carcinogenicity studies by altering survival or tumor incidence. Nevertheless, viral infections did not cause consistent adverse effects on survival or tumor prevalence in control F344 rats from 28 NCI-NTP studies, though body weights were reduced by Sendai and pneumonia viruses of mice (Rao et al., 1989). The probability of such infections can be minimized by using viral-antibody-free animals, which are readily available. 

Chickenpox Chickenpox is a highly contagious viral infection that causes rash-like blisters on the skin surface and mucous membranes. It is generally mild and not normally life-threatening. For adults, the symptoms are more serious and uncomfortable than for children. The disease can also be deadly for some people, such as pregnant women, people with leukemia, or immunosuppressed patients. Varivax (varicella virus vaccine live) from Merck Co. was tested on about 11,000 children and adults and was approved by the FDA in March 1995 as a chickenpox vaccine. 

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