Airborne transmitted infections - influenza, measles, scarlet fever, parotitis. Organ site pathomorphology
Influenza
Influenza = single stranded RNA virus that can be type A, B or C. The type A form is a major cause of epidemics thanks to hemagglutinin mutation, antigenic drift, that allows the virus to morph and evade existing immunity. Vaccine is available for those that are most at risk.
Some strains are particularly dangerous, H5N1 (bird flu) virus and H1N1, swine flu virus are notable examples. Influenza virus can go on to cause influenza pneumonia. Airways show mucosal hyperemia with lymphocyte, histocyte and plasma cell infiltrates. Various respiratory and systemic symptoms (fever, myalgia, tiredness).
Measles
Causes an acute febrile illness with upper respiratory symptoms and maculopapular rash, spread via air droplets, it is a highly infectious virus that can cause pneumonia, bronchiolitis and other airway diseases.
Microscopic observation is that of epithelial giant cells with viral inclusions, nuclei may contain single Cowdry type A inclusion and reticuloendothelial giant cells may be found in lymphoid tissue.
H&E, measles pneumonia: multinucleated epithelial giant cell (centre) with eosinophilic viral inclusions.
Image: “Measles pneumonia - Histopathology” by Photo Credit: Content Providers(s): CDC/ Dr. Edwin P. Ewing, Jr., Public domain, via Wikimedia Commons.
Remember: the multinucleated giant cells in measles lymphoid tissue are Warthin-Finkeldey cells. Clinically, Koplik spots - small white spots on the buccal mucosa opposite the molars - appear a day or two before the rash and are characteristic of measles.
Scarlet fever
A disease which can occur due to group A strep pyogenes infection. Symptoms include swollen lymph nodes, rash (feels like sandpaper), and red and bumpy tongue. Usually secondary to strep throat or streptococcal skin infections. The additional symptoms (compared to simply streptococcus pharyngitis) such as rash are due to erythrogenic toxin produced by the bacteria.
Diagnosis based on clinical findings plus throat culture or antigen detection test.
Parotitis
Inflammation of the parotid salivary gland. Bacterial (suppurative) parotitis is mostly due to S.aureus, favoured by dehydration. Bacterial causes are generally unilateral, non-bacterial are bilateral. Associated with poor oral hygiene and dehydration, symptoms include chills, fever, tachycardia and a risk of sepsis.
Parotitis also occurs in mumps, the most common viral cause. Paramyxovirus causes mumps and can cause the parotid gland to swell. Can also occur in Sjogren’s syndrome (autoimmune) and blockage (possibly due to mucus plug or tumour)