Viral Diseases:

Introduction

• This section discusses viral diseases caused by many type of viruses, those preventable by vaccines, and others causing distinct type of syndromes.
• Rickettsial illnesses and Kawasaki disease are also included. Disorders caused by hepatotropic viruses , €€papillomaviruses , and HIV (see Gynecology and Infectious Diseases: HIV , mumps  are dealt with elsewhere.

Viral Diseases Clinical Diagnosis

• Some viral illnesses present with typical symptom  like -measles, mumps, and chickenpox. In many others, the clinical picture suggests any of a number of viruses.
• For example, aseptic meningitis can be caused by the mumps virus, lymphocytic €€choriomeningitis virus, and several other enteroviruses, among others. Symptoms of respiratory disease with many viruses are indistinguishable.
• Some viral diseases have a characteristic type of rash, although in most cases the rash associated with viral syndromes is not pathognomonic.

• Several techniques are used for diagnosis, including stain in , cell culture €coxsackievirus in suckling mice., immunologic detection €seroconversion with arboviruses, rabies virus on skin biopsy, detection of secretory€ immunoglobulin A [
• IgA]), or molecular techniques such as polymerase chain reaction (PCR) (for herpes simplex virus [HSV]) or antigen assays (for cytomegalovirus [CMV]).
• Isolation of virus from a normally sterile site (cerebrospinal fluid, lung) or from a lesion (vesicles) in an immunocompetent individual is diagnostically significant. Isolation from nonsterile sites (nasopharynx, stool) may represent a carrier state, and seroconversion and pathologic change are needed to establish a diagnosis.

Microscopic Methods of Viral Diseases investigation–

• Microscopic techniques are used to examine cells, body fluids, or biopsy material in search of virus or cytopathic changes specific for one virus or a group of viruses (eg, multinucleated giant cells at the base of herpes lesions, rotavirus structures on electron micrographs of diarrheal stools).
• Immunofluorescent methods, often with monoclonal antibodies, can rapidly identify some antigens (rabies, varicella, herpes simplex, RSV) in desquamated or scraped cells.

Immunologic Studies of Sera

• Specific antibodies to viruses rise during the course of illness, though the rise and persistence of titer depend on both the virus and the host response. A fourfold or greater rise in antibody titer during illness is considered evidence of disease.
• Single determinations are seldom helpful, and laboratories require paired sera (acute and convalescent, typically 2–3 weeks apart). Antigenic detection is used for certain viruses (hepatitis B surface antigen [HBsAg], CMV, HIV), with viral presence detected independently of disease duration or host response.
• As more is learned of the natural history of HSV-1 and HSV-2 infections, these viruses are increasingly managed clinically with support from serologic data.
• Quantification of viral antigen titer is useful in the management of HIV disease and is becoming a standard of care for other chronic viral infections (eg, hepatitis B and C virus [HBV, HCV]).

Molecular €€Techniques

• Molecular technology has provided €€techniques such as PCR and nucleic acid probes that have proved useful in the identification of new pathogens €€
• €€, HCV and Kaposi’s sarcoma herpesvirus€€) as well as for the management of patients in whom quantification of viral activity, €€as with immunologic techniques, assists in following the course of clinical illness or the response to therapy. Results vary among laboratories.

Viral Diseases Treatment

• The €€armamentarium of antiviral therapy has expanded greatly with the advent of the HIV outbreak , though for many viruses there remains no definitive antiviral therapy.
• The mainstay of controlling viral diseases is vaccination. Currently available live vaccines include those against measles, mumps, rubella, €poliovirus (€€Sabin vaccine)€€, yellow fever, and varicella.
• The inactivated vaccines protect against the agents implicated in poliovirus (Salk vaccine), hepatitis A, hepatitis B, influenza A and B, rabies, €respiratory syncytial virus (€€RSV), and Japanese B encephalitis. €€Passive immunoprophylaxis remains important in prevention of hepatitis A and B,€€ RSV infection and, among the immunosuppressed, varicella. €€
• There is now a trend favoring the combination of vaccines, with the sacrifice in immunogenicity compensated for by the increased €€compliance with vaccinations by the vaccinated patient and their families.