Virology

• Human herpesviruses include: Herpes simplex 1 and 2, Varicella-Zoster, Epstein Barr virus, Human cytomegalovirus, HHV6 and 7, and HHV8 (Kaposi sarcoma associated virus)
• Successful human parasites have a high prevalence of infection, minimal clinical disease, infection early in life, and milder disease
• Herpes Simplex 1 and 2 primarily affect the skin or mucous membranes, causing lesions like vesicles, with HSV1 affecting oral areas and sometimes genital areas, while HSV2 mainly affects the genital area
• Almost 100% of adults have antibodies to HSV1, while 20-40% have antibodies to HSV2
• Primary infection with herpes simplex viruses can be asymptomatic, with vesicles developing 1-3 days post-exposure at the site of inoculation
• Genital herpes caused by HSV2 can lead to aseptic meningitis in adults
• Latency of herpes simplex viruses occurs in sensory neurons in the dorsal root ganglion and reactivation can be provoked by factors like sunlight, stress, febrile illness, menstruation, and immunosuppression
• Rare life-threatening complications of HSV infection include disseminated infection, liver failure, acute respiratory distress syndrome, multi-organ failure, neonatal HSV infection, and HSV encephalitis
• Laboratory diagnosis of HSV infections involves serology testing for IgG antibodies indicating past infection and virus detection through PCR from lesion swabs
• Varicella Zoster virus causes varicella (chickenpox) as a primary infection and reactivates as zoster (shingles), with transmission occurring through droplet spread of vesicle fluid
• Varicella infection can lead to complications like secondary skin infections, pneumonia, haemorrhagic varicella, CNS issues like post-infectious encephalomyelitis and stroke, and congenital varicella syndrome if the mother is infected during pregnancy
• Zoster, the reactivation of Varicella Zoster virus, occurs many years post-primary infection and can be triggered by factors like immunosuppression, old age, cancer, and HIV
• Treatment for HSV and VZV infections includes Aciclovir, a nucleoside analogue that interferes with DNA polymerase, with higher doses needed for VZV infections
• Post-exposure prophylaxis for varicella involves Zoster immune globulin (ZIG) for exposed individuals like immunocompromised persons, neonates, babies under 6 months, and pregnant women
• Human cytomegalovirus infection is common, with 70-90% of adults having antibodies, transmission occurring through close contact, and clinical syndromes ranging from subclinical to infectious mononucleosis-like illness
• CMV infection in immunosuppressed patients can lead to complications like interstitial pneumonia, retinitis, GIT ulceration, and brain encephalitis
• CMV is the commonest viral cause of congenital abnormalities, with fetal exposure potentially leading to congenital CMV disease with symptoms like mental retardation, deafness, and more
• Cytomegalovirus (CMV) inclusion disease is associated with symptoms like pneumonias, retinitis, gastrointestinal ulceration, and brain encephalitis
• CMV affects immunosuppressed patients such as transplant patients, those undergoing chemotherapy, using steroids for inflammatory bowel disease, late-stage HIV in adults, and HIV-infected infants
• Laboratory diagnosis of CMV includes serology with IgG indicating exposure, while IgM is an unreliable marker of current infection
• Treatment for life-threatening CMV infection involves drugs like Ganciclovir/Valganciclovir as the first choice, with alternative options like Foscarnet and Cidofovir available but toxic
• Epstein Barr virus (EBV) causes infectious mononucleosis with symptoms like fever, malaise, rash, and generalised lymphadenopathy
• Differential diagnosis of infectious mononucleosis includes primary HIV or CMV infection, and other viral infections like tonsillitis or toxoplasmosis
• EBV infects oral and nasopharyngeal epithelium during primary infection and can persist, leading to conditions like oral hairy leukoplakia in immunosuppressed patients
• Human Herpesvirus 6 (HHV6) is a universal human infection with patterns of primary infection, latency, and reactivation, causing diseases like Roseola Infantum
• Human Herpesvirus 8 (HHV8) shares similarities with EBV, latency in B cells and endothelial cells, causing conditions like Kaposi sarcoma and Multicentric Castleman's disease
• There are 8 human herpesviruses, including:

  • Herpes simplex 1 and 2
  • Varicella-Zoster
  • Cytomegalovirus
  • Epstein Barr virus
  • HHV6 and 7
  • HHV8 (Kaposi sarcoma associated virus)
• Human herpesviruses are enveloped ds DNA viruses that cause lifelong infections by establishing latency and periodic shedding in body fluids, facilitating human-to-human transmission
• Herpes Simplex 1 and 2 cause lesions and are spread through direct contact with lesions, with HSV 1 usually causing oro-facial lesions and HSV 2 usually causing genital lesions
• HSV persists in the body through latency in sensory ganglia that innervate the skin at the site of the primary lesion, with reactivation commonly provoked by sunlight, stress, febrile illness, menstruation, and immunosuppression
• Recurrent HSV lesions include cold sores, recurrent genital herpes, and recurrent keratitis
• Rare life-threatening HSV diseases include neonatal herpes, which can present as sepsis with subtle vesicles, and can lead to disseminated infection
• Diagnosis of HSV infections in the laboratory involves virus detection through culture or PCR, with IgG antibodies providing evidence of exposure
• Varicella Zoster Virus causes varicella (chicken-pox) and reactivation syndrome known as Zoster (shingles), with complications including secondary skin infections, pneumonia, post-infectious encephalomyelitis, and stroke
• Maternal varicella during pregnancy can lead to severe varicella in the baby if exposed before maternal antibodies can cross the placenta, with outcomes varying based on the timing of maternal infection
• VZV persists in the body through latency in sensory neurons in the dorsal root ganglion and spinal cord
• Zoster clinical features include vesicular eruptions in a dermatomal pattern, with complications like post-herpetic neuralgia, encephalitis, myelitis, and strokes
• Diagnosis of VZV involves serology for IgG antibodies and virus detection through culture or PCR
• Aciclovir is a drug used to treat HSV and VZV infections by interfering with DNA polymerase chain termination
• Preventing varicella in exposed individuals can be done through varicella vaccine as pre-exposure prophylaxis