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Microbiology
Table of Contents
Unit 21 Overview: Skin and Eye Infections
21.1 Anatomy and Normal Microbiota of the Skin and Eyes
21.2 Bacterial Infections of the Skin and Eyes
21.3 Viral Infections of the Skin and Eyes
21.4 Mycoses of the Skin
21.5 Protozoan and Helminthic Infections of the Skin and Eyes

🦠microbiology review

21.3 Viral Infections of the Skin and Eyes

Citation:

Viral skin infections can be a real pain, causing unsightly warts and painful cold sores. These pesky viruses spread through contact and can hide in our bodies, popping up again when we least expect it. Understanding how they work helps us fight back and keep our skin healthy.

Kids often get viral rashes that might look scary but are usually harmless. Roseola and fifth disease are common culprits, each with its own unique pattern. Knowing the differences can help parents stay calm and care for their little ones during these itchy, spotty episodes.

Viral Skin Infections

Transmission and treatment of viral skin infections

  • Warts caused by human papillomavirus (HPV)
    • Transmission through direct contact with infected skin or indirect contact with contaminated surfaces (public showers, swimming pools)
    • Symptoms include rough, bumpy skin growths most commonly appearing on hands, feet, and face
    • Treatment options: over-the-counter salicylic acid or cryotherapy, prescription topical medications (imiquimod, fluorouracil), surgical removal or laser therapy for persistent cases
  • Cold sores caused by herpes simplex virus type 1 (HSV-1)
    • Transmission through direct contact with infected saliva or skin lesions, sharing personal items (utensils, towels, lip balm)
    • Symptoms: tingling or burning sensation before lesions appear, fluid-filled blisters on or around the lips that rupture and form a crust, healing within 2-4 weeks
    • Treatment with antiviral medications (acyclovir, valacyclovir) to reduce severity and duration, topical creams or ointments to alleviate symptoms, pain relievers and cold compresses for discomfort
    • Antiviral resistance may develop in some cases, requiring alternative treatment approaches

Viral mechanisms for recurring lesions

  • HSV-1 and HPV establish latent infections in host cells
    • HSV-1 remains dormant in sensory nerve ganglia while HPV persists in the basal layer of the epithelium
    • Latent infections allow viruses to evade the immune system by maintaining viral genome in host cells with minimal viral protein expression, reducing immune recognition
  • Reactivation of latent viruses leads to recurring skin lesions
    • Triggers for HSV-1 reactivation include stress, illness, and UV exposure while HPV reactivation is associated with immunosuppression and hormonal changes
    • Reactivated viruses replicate and spread to the skin surface: HSV-1 travels along sensory nerves to the original site of infection, HPV-infected basal cells divide and differentiate carrying the virus to the surface
  • Recurrent lesions develop as the virus replicates in the skin
    • Cold sores form due to HSV-1 replication in epithelial cells
    • Warts appear as HPV-infected cells proliferate and form a thickened, keratinized layer
  • Viral tropism influences the specific skin areas affected by different viruses

Viral Exanthems in Children

Rashes of roseola vs fifth disease

  • Roseola caused by human herpesvirus 6 or 7
    • Primarily affects infants and young children (6 months to 2 years)
    • Symptoms: high fever (> 39.5°C or 103°F) lasting 3-5 days, sudden onset of pink, maculopapular rash on the trunk spreading to neck, face and limbs after fever subsides, rash fades within 1-2 days
    • Other features: febrile seizures may occur due to high fever, enlarged lymph nodes and mild upper respiratory symptoms
  • Fifth disease caused by parvovirus B19
    • Commonly affects school-aged children (5-15 years)
    • Symptoms: "slapped cheek" appearance with bright red, confluent rash on cheeks, lacy, reticular rash on the trunk and limbs that may be itchy and recur for several weeks, mild prodromal symptoms (low-grade fever, headache, malaise)
    • Other features: arthralgia or arthritis may occur especially in adults, rarely causes complications in healthy children, risk of fetal anemia and hydrops fetalis in pregnant women
    • Incubation period typically lasts 4-14 days before symptoms appear

Viral Pathogenesis and Epidemiology

  • Viral pathogenesis involves multiple stages:
    • Entry and initial replication in host cells
    • Spread to target tissues
    • Cellular damage and host immune response
    • Virus shedding and transmission to new hosts
  • Epidemiology of viral skin infections:
    • Prevalence and distribution vary by virus type and geographic region
    • Seasonal patterns may influence infection rates
    • Age-specific susceptibility affects disease occurrence in different populations

Key Terms to Review (75)

Acyclovir: Acyclovir is an antiviral medication used to treat infections caused by herpes viruses, including genital herpes, cold sores, shingles, and chickenpox. It works by inhibiting the replication of viral DNA.
Circoviridae: Circoviridae is a family of small, non-enveloped viruses with circular single-stranded DNA genomes. They are known to infect both animals and plants, causing various diseases.
Common warts: Common warts are benign skin growths caused by the human papillomavirus (HPV). They typically appear on hands and fingers but can occur anywhere on the body.
Cryotherapy: Cryotherapy is a treatment method that uses extreme cold to destroy abnormal or diseased tissue, including lesions caused by viral infections in the reproductive system. It is commonly applied using liquid nitrogen.
Epidermis: The epidermis is the outermost layer of the skin, serving as a protective barrier against environmental threats and pathogens. It is composed primarily of keratinocytes and lacks blood vessels.
Erythema infectiosum: Erythema infectiosum, also known as fifth disease, is a mild viral infection caused by human parvovirus B19. It commonly presents with a distinctive ‘slapped cheek’ rash on the face.
Famciclovir: Famciclovir is an antiviral medication used to treat herpes virus infections, including shingles and genital herpes. It works by inhibiting viral DNA replication.
Fifth disease: Fifth disease is a contagious viral infection caused by parvovirus B19 that primarily affects children. It is characterized by a distinctive facial rash that resembles a slapped cheek.
Filiform warts: Filiform warts are a type of common wart caused by the human papillomavirus (HPV). They typically appear as small, thread-like growths on the face, neck, or eyelids.
Flat warts: Flat warts are small, smooth, slightly raised bumps that generally occur in clusters and are caused by certain strains of the human papillomavirus (HPV). They are most commonly found on the face, neck, hands, wrists, and knees.
Ganciclovir: Ganciclovir is an antiviral medication used to treat cytomegalovirus (CMV) infections, particularly in immunocompromised individuals. It works by inhibiting viral DNA replication.
Genital herpes: Genital herpes is a sexually transmitted infection (STI) caused by the herpes simplex virus type 1 (HSV-1) or type 2 (HSV-2). It results in painful sores and blisters on the genital and anal areas.
Herpetic keratitis: Herpetic keratitis is an infection of the cornea caused by the herpes simplex virus (HSV). It can lead to eye pain, redness, blurred vision, and potentially result in blindness if untreated.
Herpetic whitlow: Herpetic whitlow is a painful, viral infection of the fingers caused by the herpes simplex virus (HSV). It commonly affects healthcare workers and individuals with HSV-1 or HSV-2 infections.
Herpes gladiatorum: Herpes gladiatorum is a skin infection caused by the herpes simplex virus, commonly affecting athletes involved in contact sports. It is characterized by painful vesicular lesions on the skin.
Herpes simplex virus type 1 (HSV-1): Herpes simplex virus type 1 (HSV-1) is a contagious virus that predominantly causes oral herpes, leading to cold sores and fever blisters around the mouth. It can be transmitted through direct contact with infected saliva or lesions.
Herpes keratitis: Herpes keratitis is an infection of the cornea caused by the herpes simplex virus (HSV). It can lead to pain, redness, blurred vision, and can result in scarring or vision loss if untreated.
Herpes simplex virus (HSV): Herpes simplex virus (HSV) is a viral pathogen that causes infections in the skin, mucous membranes, and eyes. There are two main types: HSV-1, associated with oral herpes, and HSV-2, primarily responsible for genital herpes.
HSV-1 and HSV-2: HSV-1 (Herpes Simplex Virus type 1) and HSV-2 (Herpes Simplex Virus type 2) are viral pathogens that cause infections primarily affecting the skin and mucous membranes. HSV-1 is commonly associated with oral infections, while HSV-2 typically causes genital infections.
HPV: HPV (Human Papillomavirus) is a group of viruses that infect the skin and mucous membranes. Certain strains are associated with cancer, particularly cervical cancer.
Human papillomavirus (HPV): Human papillomavirus (HPV) is a group of related viruses, some of which can cause genital warts and cancers such as cervical cancer. It is one of the most common sexually transmitted infections globally.
Humoral immunity: Humoral immunity is a component of the adaptive immune system that involves the production of antibodies by B cells. These antibodies circulate in the blood and lymphatic system to neutralize pathogens.
Human herpesvirus: Human herpesvirus (HHV) is a group of DNA viruses responsible for causing various infections in humans, including those affecting the skin and eyes. These viruses are characterized by their ability to establish latent infections and reactivate later.
Imiquimod: Imiquimod is an immune response modifier used topically to treat certain viral infections, including genital warts caused by human papillomavirus (HPV). It works by stimulating the body's immune system to fight the virus.
Incubation period: The incubation period is the time interval between exposure to a pathogen and the appearance of the first symptoms. It is a critical phase in understanding disease transmission and prevention.
Keratoconjunctivitis: Keratoconjunctivitis is an inflammation of both the cornea and conjunctiva, typically caused by infections, allergens, or irritants. It can result in symptoms such as redness, pain, and visual disturbances.
Macules: Macules are flat, distinct, discolored areas of skin less than 1 centimeter wide without any change in texture or thickness. They are often a sign of underlying infections or conditions affecting the skin.
N-docosanol: n-Docosanol is a saturated fatty alcohol used as an antiviral agent, primarily for treating herpes simplex virus infections. It inhibits the fusion between the host cell membrane and the viral envelope, preventing viral entry into cells.
Papillomaviridae: Papillomaviridae is a family of non-enveloped, double-stranded DNA viruses known to cause papillomas (warts) in humans and animals. These viruses are capable of infecting skin and mucous membranes.
Oral herpes: Oral herpes is a viral infection caused by the herpes simplex virus type 1 (HSV-1) that typically manifests as cold sores or fever blisters around the mouth and lips. It is highly contagious and can spread through direct contact with infected saliva or lesions.
Parvovirus B19: Parvovirus B19 is a small, single-stranded DNA virus that primarily infects humans, causing erythema infectiosum (fifth disease) and other clinical manifestations. It is known for its characteristic 'slapped cheek' rash in children.
Papules: Papules are small, raised, solid pimples or swellings on the skin that do not contain pus. They are often caused by inflammation or infection and can be a sign of various skin conditions.
Papillomas: Papillomas are benign growths caused by the human papillomavirus (HPV) that can appear on the skin and mucous membranes. They are often referred to as warts.
Penciclovir: Penciclovir is an antiviral medication used to treat herpes simplex virus infections, particularly cold sores. It works by inhibiting viral DNA replication, thus controlling the spread of the virus.
Plantar warts: Plantar warts are benign skin growths caused by the human papillomavirus (HPV) that appear on the soles of the feet. They are typically hard and flat with a rough surface and well-defined boundaries.
Polyomaviridae: Polyomaviridae is a family of small, non-enveloped DNA viruses known to infect mammals and birds. Some members of this family can cause skin and eye infections in humans.
Salicylic acid: Salicylic acid is a beta hydroxy acid that is commonly used in the treatment of skin conditions, especially acne. It has keratolytic properties, helping to exfoliate the skin and reduce inflammation.
Roseola: Roseola is a common viral infection in young children characterized by a sudden high fever followed by a distinctive rash. It is mainly caused by human herpesvirus 6 (HHV-6) and sometimes human herpesvirus 7 (HHV-7).
Valacyclovir: Valacyclovir is an antiviral medication used to treat infections caused by herpes viruses, including herpes simplex virus (HSV) and varicella-zoster virus (VZV). It is a prodrug that is converted into acyclovir in the body, which then inhibits viral DNA polymerase.
Viral conjunctivitis: Viral conjunctivitis, also known as pink eye, is an inflammation of the conjunctiva caused by viral infection. It is highly contagious and often accompanies upper respiratory infections.
Warts: Warts are small, benign skin growths caused by various strains of the human papillomavirus (HPV). They typically appear on the hands, feet, and other areas and are highly contagious.
Acyclovir: Acyclovir is an antiviral medication primarily used to treat infections caused by the herpes simplex virus, including cold sores, genital herpes, and shingles. It works by inhibiting the replication of the viral DNA, effectively preventing the virus from spreading and causing further infection.
Incubation Period: The incubation period refers to the time between when an individual is exposed to an infectious agent and when they begin to show symptoms of the resulting disease. This period is crucial in understanding the progression and transmission of infectious diseases across various contexts.
Immune Evasion: Immune evasion refers to the strategies employed by pathogens to circumvent, subvert, or suppress the host's immune defenses, allowing them to establish and maintain infection. This term is crucial in understanding how pathogens cause disease, the virulence factors they possess, and the mechanisms behind viral infections in various body systems.
Humoral Immunity: Humoral immunity refers to the antibody-mediated immune response, which involves the production of antibodies by B lymphocytes to neutralize and eliminate extracellular pathogens and toxins. It is a crucial component of the adaptive immune system that provides long-lasting protection against specific antigens encountered by the body.
Cell-Mediated Immunity: Cell-mediated immunity is an immune response that involves the activation of specialized T cells to eliminate pathogens or infected cells. It is a crucial component of the adaptive immune system, working in conjunction with humoral immunity to provide comprehensive protection against a wide range of threats, including viral infections, intracellular bacteria, and certain types of cancer.
Epidermis: The epidermis is the outermost layer of the skin, serving as a protective barrier against environmental threats and preventing water loss from the body. It is a crucial component of the skin's anatomy and plays a vital role in the normal microbiota and viral infections affecting the skin and eyes.
Imiquimod: Imiquimod is a synthetic immune response modifier that acts as a toll-like receptor agonist, primarily targeting the TLR7 receptor. It is used in the treatment of various viral skin infections and as an adjuvant in certain immunotherapies.
Fluorouracil: Fluorouracil is a chemotherapeutic agent that is commonly used in the treatment of various types of cancer, including skin and eye cancers. It works by interfering with the synthesis of DNA, ultimately leading to the death of rapidly dividing cancer cells.
Human Herpesvirus 7: Human herpesvirus 7 (HHV-7) is a member of the Herpesviridae family, which is a group of DNA viruses that can cause a variety of skin and eye infections in humans. HHV-7 is primarily associated with roseola, a common childhood illness characterized by a distinctive rash.
Parvovirus B19: Parvovirus B19 is a small, non-enveloped DNA virus that primarily infects and destroys human erythroid progenitor cells, leading to various clinical manifestations related to viral infections of the skin and eyes.
Roseola: Roseola is a common childhood viral infection that typically causes a distinctive red rash and fever. It is primarily associated with infections of the skin and eyes, making it an important topic within the context of viral infections of these areas.
Hydrops Fetalis: Hydrops fetalis is a condition characterized by the abnormal accumulation of fluid in two or more fetal compartments, such as the skin, abdomen, or chest cavity. It is a severe and potentially life-threatening condition that can occur during pregnancy and is often associated with various underlying medical conditions or genetic disorders.
Antiviral Resistance: Antiviral resistance refers to the ability of viruses to adapt and become less susceptible to the effects of antiviral drugs or other interventions designed to inhibit viral replication and infection. This phenomenon is particularly relevant in the context of viral infections of the skin and eyes, where antiviral treatments are commonly used.
Fifth Disease: Fifth disease, also known as erythema infectiosum, is a viral infection caused by the human parvovirus B19. It is characterized by a distinctive red rash that appears on the face, giving the appearance of a 'slapped cheek' look, and can spread to the rest of the body.
Latent Infections: Latent infections refer to a state where a pathogen, such as a virus, remains dormant or inactive within the host's cells without causing any immediate symptoms or signs of disease. This quiescent state allows the pathogen to evade the host's immune defenses and persist in the body, potentially reactivating at a later time to cause recurrent or reactivated infections.
Basal Layer: The basal layer, also known as the stratum basale, is the deepest layer of the epidermis, the outermost layer of the skin. It serves as the foundation for the other epidermal layers and is responsible for the continuous regeneration of the skin through the proliferation and differentiation of keratinocytes.
Papillomavirus: Papillomaviruses are a group of small, non-enveloped DNA viruses that primarily infect the skin and mucosal surfaces of the body. They are known to cause a variety of benign and malignant lesions, particularly in the context of viral infections of the skin and eyes.
HPV (Human Papillomavirus): HPV, or Human Papillomavirus, is a group of viruses that can infect the skin and mucous membranes, leading to various viral infections, including those affecting the skin, eyes, and reproductive system. HPV is a significant public health concern due to its association with certain types of cancers, making it an important topic in the context of viral infections covered in the chapters 21.3 and 23.4.
Valacyclovir: Valacyclovir is an antiviral medication used to treat viral infections, particularly those caused by the herpes simplex virus (HSV) and varicella-zoster virus (VZV). It is a prodrug that is converted to the active form, acyclovir, within the body, allowing for more efficient absorption and increased bioavailability compared to oral acyclovir.
Human Herpesvirus 6: Human herpesvirus 6 (HHV-6) is a member of the Herpesviridae family of viruses, which are known for their ability to establish lifelong latent infections in the host. HHV-6 is closely associated with viral infections of the skin and eyes, as outlined in the topics of 21.3 Viral Infections of the Skin and Eyes.
Febrile Seizures: Febrile seizures are a type of convulsive episode that occurs in young children, typically between the ages of 6 months and 5 years, and is triggered by a rapid rise in body temperature or fever. These seizures are a common and usually harmless response to a fever, often associated with viral infections affecting the skin and eyes.
Herpesvirus: Herpesviruses are a family of DNA viruses that can cause a variety of viral infections, particularly affecting the skin and eyes. These viruses are known for their ability to establish lifelong latent infections within the host's cells, leading to recurrent outbreaks of symptoms.
Sensory Nerve Ganglia: Sensory nerve ganglia are clusters of nerve cell bodies located outside the central nervous system that receive and transmit sensory information from various parts of the body to the brain. They play a crucial role in the perception and processing of sensory stimuli, such as touch, temperature, and pain.
Maculopapular Rash: A maculopapular rash is a type of skin eruption characterized by the presence of both macules (flat, discolored spots) and papules (raised, solid bumps) on the skin. This type of rash is commonly associated with various viral infections affecting the skin and eyes.
HSV-1: HSV-1, or Herpes Simplex Virus Type 1, is a common viral infection that primarily affects the skin, mouth, and eyes. It is a member of the Herpesviridae family and is known for its ability to establish latent infections in the host's nervous system, leading to recurrent outbreaks.
Cryotherapy: Cryotherapy is the local or general use of low temperatures to treat various medical conditions, including viral infections of the skin, eyes, and reproductive system. It involves the application of extreme cold to destroy abnormal or diseased tissue while preserving healthy tissue.
Viral Pathogenesis: Viral pathogenesis refers to the complex process by which viruses infect and cause disease in their host organisms. It encompasses the various mechanisms and stages involved in viral entry, replication, and the subsequent host immune response that can lead to the development of clinical symptoms and pathological conditions.
Envelope Glycoproteins: Envelope glycoproteins are proteins embedded within the viral envelope, the outermost layer of certain viruses. These glycoproteins play a crucial role in the attachment and entry of viruses into host cells, making them essential for viral infection and transmission.
Lymphadenopathy: Lymphadenopathy refers to the abnormal enlargement or swelling of lymph nodes, which are small, bean-shaped organs that are part of the lymphatic system. This condition can occur in response to various viral infections that affect the skin, eyes, circulatory, and lymphatic systems.
Arthralgia: Arthralgia is the medical term for joint pain or discomfort. It is a common symptom that can occur in various viral infections, particularly those affecting the skin and eyes.
Arthritis: Arthritis is a broad term that describes inflammation of the joints, often leading to pain, stiffness, and reduced mobility. It is a common condition that can affect various aspects of viral infections, particularly those involving the skin and eyes.
Capsid: The capsid is the protein shell that encloses the genetic material of a virus. It is a crucial structural component that protects the viral genome and facilitates the virus's ability to infect host cells during the viral life cycle.
Epidemiology: Epidemiology is the study of the distribution and determinants of health-related states or events in specified populations, and the application of this study to the control of health problems. It is a fundamental science of public health that investigates the patterns, causes, and effects of diseases and other factors related to health in defined populations.
Viral Tropism: Viral tropism refers to the specific affinity a virus has for certain host cells or tissues, which determines the sites of viral infection and replication. This concept is crucial in understanding the pathogenesis and tissue tropism of different viruses, as well as their potential for causing disease in various organs and systems.