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Acute (Transient) Infections
- wide variation in surface morphology
- efficient detection and elimination by body
- different ability to reinfect the host - not all Ab offer long-lasting protection, strains w/ genetic variation/morphologic differences
Examples of Acute (Transient) Infections
- affects numerous organ systems
- mild to severe illness
- singlestranded RNA paramyxovirus
- effective vaccine (MMR)
- transmitted via respiratory droplets
- replicates in respiratory tract cells (particularly epithelial cells and lymphocytes), and spread to regional lymphoid tissue; viral proliferation leads to vascular spread and residence in a variety of tissues, including skin, conjunctiva, and the CNS
- T cell mediated immunity results in characteristic rash
- transient immunosuppression leaves host susceptible to secondary bacterial and viral infections
- Severe infections in those with defects in cell-mediated immunity, resulting in pneumonia, diarrhea, keratitis and blindness, and encephalitis
- antibodies are protective
Measles (rubeola) - Clinical features
- blotchy erythematous cutaneous rash on the face, trunk, and proximal extremities
- Koplik spots, areas of white/gray punctate necrosis, on oral mucosa
- hyperplastic lymphoid organs w/ Warthin-Finkeldey giant cells, pathognomonic
- swelling salivary glands
- spread through respiratory droplets
- gain access to respiratory lymphoid tissue and replicate preferentially in activated T lymphocytes. disseminated to tissue via bloodstream
- Salivary gland ductal cells become damaged, leading to inflammation and edema, and the classic salivary gland pain and swelling.
- Other affected organs include the gonads, pancreas, and CNS.
- ~15% cases present with aseptic meningitis
- MMR vaccine effective
Mumps - Clinical features
- 70% show bilateral parotitis; salivary parenchyma diffusely infiltrated with lymphocytes, macrophages, neutrophils, and plasma cells.
- Mumps orchitis - can lead to severe testicular damage (space within the tunica albuginea is restricted, enlargement can lead to vascular compromise and subsequent necrosis, scarring, and possible sterility).
- Mumps pancreatitis - can cause damage to the organ, with release of digestive enzymes and necrosis of the pancreas and surrounding fat.
- Mumps encephalitis - demyelination and inflammation of CNS
- persistent viral genome present within certain cells in the absence of active infection
- may be activated at a later time, resulting in proliferation and disease
- most common - Herpes virus (dsDNA, ubiquitous in humans)
Herpes simplex viruses (HSV-1 and HSV-2)
- replicate in the skin and mucosa at the site of entry
- primary infection - clustered fluid-filled vesicles, pruritic or painful
- then migrates through sensory nerve axons to take up residence (and thereby establish latent infection) in the ganglia supplying that patch of infected skin or mucosa
- primary infection resolves
- Reactivation - later, often associated with stimuli such as exposure to cold, sunlight, or stress.
- Mucocutaneous lesion then recur, with the potential for much more severe sequelae, such as corneal blindness and encephalitis
- Disseminated disease can occur in neonates and the immunocompromised
Herpes simplex viruses (HSV-1 and HSV-2) - Clinical features
- oral manifestation of primary HSV-1 infection - herpetic gingivostomatitis. clustered vesicles/ ulcerations mainly on the attached gingiva and hard palate, and gingival swelling.
- Systemic signs of a viral illness (fever, malaise, etc.) will also be present.
- recurrent infection - herpes labialis (aka cold sores)
- Primary HSV-2 infection - development of genital herpes.
- Infection under fingernails - herpetic whitlow
- HSV infection of the eyes can cause direct damage to the corneal epithelial cells, or result in inflammation, neovascularization, scarring, and eventual blindness.
- other organ systems can be infected with HSV, resulting in organ damage and occasionally failure.
Varicella-Zoster virus (VZV)
- a type of herpesvirus
- spread by aerosols
- hematogenously disseminated
- acute infection - chickenpox
- recurrent infection - shingles
- infects skin, mucosa, and ultimately regional neurons.
- Following the initial, typically mild selflimited vesicular infection (chickenpox), the virus establishes latency in sensory nerve ganglia.
- Reinfection - years to decades later, manifesting as vesicles and painful ulcerations in the dermatome corresponding to the affected sensory nerve
- The most frequently involved are the trigeminal ganglia
- Recurrent VZV infection - rare, most commonly associated with immunosuppression or older age
VZV - Clinical features
- - rash develops 2 weeks following respiratory infection
- - waves of lesions begin on the torso, and progress to involve the head and extremities
- - The lesions present initially as macules, and then evolve to form vesicles that rupture, crust over, and ultimately heal without scarring
- - localized disease, affecting one or more dermatomes and perhaps some adjacent skin or mucosa
- - involved anatomic sites, facial paralysis and tooth
- devitalization are known head and neck manifestations
- - Pain, burning and intense itching are common
- - More severe sequelae: encephalitis, interstitial pneumonia, and necrotizing visceral lesions
- a range of clinical signs and symptoms, depending upon patient age and immune status
- infects monocytes and their progenitors, endothelial cells, and salivary ductal tissue, among others.
- infected cells - significantly enlarged w/ enlarged nucleus.
- In healthy individuals, CMV infection is either subclinical, or results in a mononucleosis-like illness.
- In neonates and the immunocompromised, CMV leads to a severe and widespread infection involving many tissue types.
- Infection occurs through:
- 1. placental transmission – asymptomatic mostly; if the mother has an active primary infection w/o protective antibodies, the fetus can develop cytomegalic inclusion disease, similar in presentation to erythroblastosis fetalis, w/ restricted growth, hepatosplenomegaly, thrombocytopenia, and encephalitis. Infants often have permanent neurologic deficits. Severity - mild to fatal.
- 2. neonatal transmission (i.e. during birth) – occurs by passage through birth canal or through breast milk. Typically asymptomatic due to maternal antibodies or mild.
- 3. saliva exposure – most people have been exposed and initial infection asymptomatic. In those who do develop symptoms, the disease resembles infectious mononucleosis, with patients experiencing fever, hepatosplenomegaly, lymphadenopathy, and abnormal liver function. Most recover without sequelae, but the virus will persist for life within lymphocytes.
- 4. organ transplant – involving solid organs.
- 5. sexual contact
- In the immunocompromised, CMV infection leads to severe and disseminated disease manifestations. Most commonly, lungs and gastrointestinal tract - pneumonitis and colitis. pneumonitis can develop into acute respiratory distress syndrome. Intestinal necrosis results in large areas of ulceration and severe diarrhea.
- virus transform normal cell into neoplastic one, either benign or malignant.
- Examples: HPV, HBV, and HTLV-1
Epstein-Barr virus (EBV)
- leads to the development of infectious mononucleosis, a self-limited, if somewhat severe, lymphproliferative disorder.
- also result in certain cancers, such as several types of lymphoma and nasopharyngeal carcinoma.
- spread through saliva
- infects oropharyngeal epithelial cells and then spreads to the lymphoid tissues of Waldeyer’s ring, especially the tonsils (stary-sky pattern in oral mucosa)
- specifically infects B lymphocytes, and encodes for proteins that cause a polyclonal B cell proliferation, which then migrate through the body
- Several organs will be affected:
- 1. Blood – absolute lymphocytosis with the presence of atypical cytotoxic T lymphocytes and natural killer cells.
- 2. Lymph nodes – widespread lymphadenopathy, but the cervical and axillary lymph nodes are most prominantly involved.
- 3. Spleen – grossly enlarged and prone to rupture.
- 4. Liver – enlarged due to lymphocyte infiltration of the portal areas
Epstein-Barr virus (EBV) - Clinical features
- in young children - resembles a nonspecific viral illness
- In young adults - fever, malaise, lymphadenopathy, and fatigue. In severe cases the symptoms may resemble those of leukemia or lymphoma. diagnosis is made through laboratory testing.
- self-limited but runs a rather prolonged course, lasting from 4 to 6 weeks, with the fatigue persisting.
- Severe complications include jaundice and liver failure.
- the immunosuppressed - unrestricted polyclonal B lymphocyte proliferation, eventually transforming to a monoclonal B-cell lymphoma.
- Also known to cause Burkitt’s lymphoma.