Basic Virology. Martinez J. Hewlett

the context of possible courses and outcomes. A number of specific examples are outlined in this chapter.

      Some of the basic criteria that can be incorporated into such a scheme include:

      1 Do the symptoms of the viral disease take a short or long time to develop after first encountering the virus?

      2 Are the symptoms of initial infection relatively mild or severe?

      3 Can the infected individual be expected to recover completely, or partially?

      4 Does the virus stay associated with the victim following apparent recovery?

      5 If the association is lasting, is the virus maintained in an infectious form either sporadically or constantly?

Viral diseases leading to persistence of the virus in the host are generally associated with viruses having long associations with human populations

Humans, like other animals, are subject to numerous viral infections mediated by viruses either maintained solely in the host population or in another population of animals with which humans interact. We have seen that two basic patterns occur in the course of virus replication in humans – persistent infections with incomplete virus clearing, and acute infections with efficient virus clearing upon recovery from the acute infection. It might be argued that persistent infections represent associations between virus and host that have stabilized over time, such that the viruses are maintained within the host population without a large negative effect. Conversely, acute infections may involve viruses that have recently moved from a different host. In the case of humans, such viruses may originate from zoonotic infections. While influenza A viruses and hantaviruses are examples that support this model, human rhinoviruses, among others, would not, since there are no known animal reservoirs. These virus groups and some of the symptoms caused by their infections of humans are listed in Table 4.1.

Table 4.1 Some viruses infecting humans.

Family	Genome	Primary Reservoir	How Long Associated with Humans	Virus Type	Acute Disease	Primary Infection	Mortality Rate	Persistent/Latent?	Reactivation	Chronic Disease/Complications
Herpesviridae	DNA	Humans	Ancient	HSV‐1	Facial lesion	Epidermis	Nil	Yes	Frequent at site	Encephalitis (rare)
				HSV‐2	Genital lesion	Epidermis	Nil	Yes	Frequent at site	Encephalitis (rare)
				VZV	Chickenpox	Epidermis	Nil	Yes	Once	Shingles/disseminated infection upon immune suppression
				HCMV	Mononucleosis	Hematopoietic tissue	Nil	Yes	Asymptomatic/infrequent?	Disseminated infection upon immune suppression/retinitis
				EBV	Mononucleosis	Lymphoid tissue	Nil	Yes	Asymptomatic/infrequent?	Lymphoma/carcinoma
				HHV‐6	Roseola	Lymphoid tissue	Nil	Yes	Asymptomatic/infrequent?	?
				HHV‐7	Roseola	Lymphoid tissue	Nil	Yes	Asymptomatic/infrequent?	?
				HHV‐8	?	Lymphoid tissue	Nil	Yes	Asymptomatic/infrequent?	Kaposi's sarcoma
Polyomaviridae	DNA	Humans	Ancient	JC	None	Kidney/bladder	Nil	Yes	Infrequent (?) shedding	Encephalitis upon immune suppression
				BK	None	Kidney/bladder	Nil	Yes	Infrequent (?) shedding	Kidney infection
Papillomaviridae	DNA	Humans	Ancient	>60 types	Warts	Epidermis	Nil	Yes	Constant shedding at site	Cervical carcinoma (Types 6, 11, 16, and 18)
Adenoviridae	DNA	Humans	Ancient?	>12 types	Mild respiratory	Respiratory tract	Nil	Yes	Infrequent shedding?	?
Poxviridae	DNA	Humans	Recent	Variola	Smallpox	Epidermis	Moderate to high	No	N/A	None