Many viruses involve the skin in one way or another (Table 36-4) Some, such as papillomaviruses, poxviruses, and recurrent herpes simplex, produce relatively localized crops of lesions and few if any systemic symptoms. Others, such as those causing the childhood exanthemata, produce a generalized rash as part of a wider clinical syndrome that follows a systemic infection. These rashes vary greatly in their anatomic distribution and in the morphology of the individual lesions. They are classified for convenience into maculopapu-lar, vesicular, nodular, and hemorrhagic rashes (Fig. 36-5).
Macules are flat, colored spots; papules are slightly raised from the surface of the skin but contain no expressible fluid. Virus is not shed from the lesions of maculopapular rashes. Many such rashes may in fact result from a hypersensitivity response to the virus growing in cells of the skin or capillary endothelium.
The differential diagnosis of maculopapular rashes is difficult, not only because many rashes are of foxic, allergic, or psychogenic origin, but also because they are a common feature of countless infectious diseases caused by bacteria, rickettsiae, fungi, protozoa, and metazoa as well as viruses! The rash
itself is rarely pathognomonic; the whole clinical syndrome must be taken carefully into account.
The classic standards of reference against which other rashes are compared are the so-called morbilliform rash of measles and the rubelliform rash of rubella. The exanthem of measles (Fig. 36-5C) consists of flat reddish brown macules which coalesce to form rather large blotches; after the rash fades on day 5 or 6 the skin retains a brownish stain for a time then undergoes desquamation. In contrast, the exanthem of rubella consists of much smaller (pinpoint) pink macules which tend to remain discrete, giving the rash a fine or erythematous appearance; it usually disappears after 2-3 days.
Numerous unrelated viruses produce rashes almost indistinguishable from one or another of these two prototypes. Infections with literally dozens of different enteroviruses can present as a maculopapular rash, generally in children, often during late summer epidemics. These exanthems are usually ephemeral and nonpruritic. They are mainly rubelliform or morbilliform, but can be erythematous, petechial, urticarial, or vesicular in character. Space does not allow description of the syndromes associated with each of the 30-plus enteroviruses involved. Suffice it to note that Ihe serotypes most frequently responsible for cutaneous eruptions are echoviruses 4, 9, and 16 and coxsackieviruses A9, A16, and B5.
Erythema infectiosum, or fifth disease, now known to be caused by a parvovirus, B19, is recognized for its unique rash. The child first develops flushed red cheeks, contrasting with pallor around the mouth, then a rubelliform eruption on the limbs which develops a lacelike appearance as it fades (see Fig. 17-4). Exanthem subitum, otherwise known as roseola infantum or sixth disease, is a universal exanthem of infants caused by human herpesvirus 6, although the classic rash is not always seen. About 10% of
Viral Skm Rashes
Maculopapular Measles Rubella
HHV-6 (human herpesvirus 6) Echoviruses 9, 16, many others Coxsackie A9, A16, B5, many others Epstein-Barr virus, cytomegalovirus Dengue, Chikungunya, Ross River, other arboviruses Hepatitis B Varicella-zostei Herpes simplex 1, 2
Coxsackie A9, A16; enterovirus 71; others Monkeypox Cowpox Vaccinia
Papillomaviruses Molluscum contagiosum Milker's nodes Orf
Tana pox cases ol infectious mononucleosis, whether caused by EBV or CMV, have a maculopapular rash, usually on the trunk. Many arthropod-borne togaviruses and flaviviruses, including dengue, chikungunya, Sindbis, o'nyong-nyong, Mayaro, West Nile, and Ross River viruses, also produce a maculopapular or scarlatiniform rash lasting 2-3 days. Finally, mention should be made of the urticarial rash that forms part of the serum sickness syndrome seen fleetingly in the prodromal phase of 10-20% of cases of hepatitis B.
Vesicles are blisters, containing clear fluid from which virus can readily be isolated. Vesicular rashes do not present a great diagnostic problem, particularly now that smallpox (Fig. 36-5A) has disappeared. A generalized vesicular rash in a febrile child today is usually chickenpox (varicella). The lesions occur in crops, initially concentrated on the trunk, then spreading centrifu-gally. Each vesicle progresses lo a pustule and a scab which then falls off. In herpes zoster the lesions are largely (but not necessarily exclusively) confined to a particular dermatome (Fig. 20-7), as is also the case with the recurrent —form of herpes simplex (Figs. 20-5 and 20-6). However, in the case of disseminated herpes simplex or zoster, as seen in newborn infants or immunocompromised patients, the lesions may be widespread throughout the body. Something of a curiosity is the condition known as hand-foot-and-mouth disease caused by certain coxsackieviruses, in which vesicles or even bullae occur on the palms, soles, and buccal mucosa. Coxsackie A viruses also produce a similar type of vesicular enanthem on the mucous membrane of the throat and palate ("herpangina").
Poxviruses preferentially infect the skin, producing multiple pustular or nodular lesions, as in human monkeypox and molluscum contagiosum, re
Nodular spectively, or usually single lesions such as occur in the zoonotic infections caused by orf, milker's nodes, cowpox, and tanapox viruses (see Fig. 21-5).
Papillomavirus infections were described in Chapter 18. The papilloma, or wart, is a benign hyperplastic growth, usually multiple, occurring in crops on the skin or mucous membranes. Dermatologists classify them in various ways but generally recognize common warts, flat warts, plantar and palmar warts, epidermodysplasia verruciformis, and genital warts (see Fig. 18-3), all of which are clinically distinct and tend to be caused by different human papillomavirus types (see Table 18-2).
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