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1、Herpesviruses,An Overview,Properties of herpesviruses,Enveloped double stranded DNA viruses. Genome consisits of long and short fragments which may be orientated in either direction, giving a total of 4 isomers. Three subfamilies: Alphaherpesviruses - HSV-1, HSV-2, VZV Betaherpesviruses - CMV, HHV-6
2、, HHV-7 Gammaherpesviruses - EBV, HHV-8 Set up latent or persistent infection following primary infection Reactivation are more likely to take place during periods of immunosuppression Both primary infection and reactivation are likely to be more serious in immunocompromised patients.,Herpesvirus Pa
3、rticle,HSV-2 virus particle. Note that all herpesviruses have identical morphology and cannot be distinguished from each other under electron microscopy.,(Linda Stannard, University of Cape Town, S.A.),Herpes Simplex Viruses,Properties,Belong to the alphaherpesvirus subfamily of herpesviruses Double
4、 stranded DNA enveloped virus with a genome of around 150 kb The genome of HSV-1 and HSV-2 share 50 - 70% homology. They also share several cross-reactive epitopes with each other. There is also antigenic cross-reaction with VZV. Man is the only natural host for HSV.,Epidemiology (1),HSV is spread b
5、y contact, as the virus is shed in saliva, tears, genital and other secretions. By far the most common form of infection results from a kiss given to a child or adult from a person shedding the virus. Primary infection is usually trivial or subclinical in most individuals. It is a disease mainly of
6、very young children ie. those below 5 years. There are 2 peaks of incidence, the first at 0 - 5 years and the second in the late teens, when sexual activity commences. About 10% of the population acquires HSV infection through the genital route and the risk is concentrated in young adulthood.,Epidem
7、iology (2),Generally HSV-1 causes infection above the belt and HSV-2 below the belt. In fact, 40% of clinical isolates from genital sores are HSV-1, and 5% of strains isolated from the facial area are HSV-2. This data is complicated by oral sexual practices. Following primary infection, 45% of orall
8、y infected individuals and 60% of patients with genital herpes will experience recurrences. The actual frequency of recurrences varies widely between individuals. The mean number of episodes per year is about 1.6.,Pathogenesis,During the primary infection, HSV spreads locally and a short-lived virae
9、mia occurs, whereby the virus is disseminated in the body. Spread to the to craniospinal ganglia occurs. The virus then establishes latency in the craniospinal ganglia. The exact mechanism of latency is not known, it may be true latency where there is no viral replication or viral persistence where
10、there is a low level of viral replication. Reactivation - It is well known that many triggers can provoke a recurrence. These include physical or psychological stress, infection; especially pneumococcal and meningococcal, fever, irradiation; including sunlight, and menstruation.,Clinical Manifestati
11、ons,HSV is involved in a variety of clinical manifestations which includes ;- 1. Acute gingivostomatitis 2. Herpes Labialis (cold sore) 3. Ocular Herpes 4. Herpes Genitalis 5. Other forms of cutaneous herpes 7. Meningitis 8. Encephalitis 9. Neonatal herpes,Oral-facial Herpes,Acute Gingivostomatitis
12、Acute gingivostomatitis is the commonest manifestation of primary herpetic infection. The patient experiences pain and bleeding of the gums. 1 - 8 mm ulcers with necrotic bases are present. Neck glands are commonly enlarged accompanied by fever. Usually a self limiting disease which lasts around 13
13、days. Herpes labialis (cold sore) Following primary infection, 45% of orally infected individuals will experience reactivation. The actual frequency of recurrences varies widely between individuals. Herpes labialis (cold sore) is a recurrence of oral HSV. A prodrome of tingling, warmth or itching at
14、 the site usually heralds the recurrence. About 12 hours later, redness appears followed by papules and then vesicles.,Gingivostomatitis,Ocular Herpes,HSV causes a broad spectrum of ocular disease, ranging from mild superficial lesions involving the external eye, to severe sight-threatening diseases
15、 of the inner eye. Diseases caused include the following:- Primary HSV keratitis dendritic ulcers Recurrent HSV keratitis HSV conjunctivitis Iridocyclitis, chorioretinitis and cataract,Genital Herpes,Genital lesions may be primary, recurrent or initial. Many sites can be involved which includes the
16、penis, vagina, cervix, anus, vulva, bladder, the sacral nerve routes, the spinal and the meninges. The lesions of genital herpes are particularly prone to secondary bacterial infection eg. S.aureus, Streptococcus, Trichomonas and Candida Albicans. Dysuria is a common complaint, in severe cases, there may be urinary retention. Local sensory nerves may be involved leading to the development of a radiculitis. A mild meningitis may be present. 60% of patients with genital herpes will experience r
