Pathology Mod 5: Transmission and Dissemination of Microbes PDF

PATHOLOGY 09/04/2024. MOD 5: TRANSMISSION AND DISSEMINATION OF MI...

PATHOLOGY 09/04/2024. MOD 5: TRANSMISSION AND DISSEMINATION OF MICROBES Dr. Kevin A. Elomina, MD, DPSP Trans Group/s: 4A I. MAIN ROUTES OF ENTRY (FECAL-ORAL They should be able to enter and For the infection to occur, the pathogens must FIRST ROUTE) exit the GIT. ENTER the host. Pathogens generally gain access These are the 5 main routes of entry used by microbes to the GIT through the mouth by (each having specific defense mechanisms to protect ingestion of contaminated food against infections): or water. ○ Skin Eventually, these pathogens are ○ Gastrointestinal Tract released to the environment ○ Respiratory Tract through the anus via feces. ○ Urogenital Tract ○ Vertical Transmission After entering, they should If these defense mechanisms are compromised or if the survive the harsh conditions of pathogen can overcome such intact defense the GIT. mechanisms, INFECTION OCCURS. The highly acidic environment It is important to know the transmission and general of the stomach prevents survival principles of microbial pathogenesis/infectious diseases of most microbes. for the proper infection control measures to be instituted, Protective mechanisms of GIT preventing the chain of transmission. ○ Intestinal mucus covers the intestinal epithelium to A. SKIN prevent access to intestinal An excellent barrier against external pathogens. epithelium. If the pathogen can penetrate intact skin or thrive in the ○ Pancreatic enzymes & bile keratinous layer of the skin, infection can also occur in detergents act as the setting of an intact skin. biomolecules. ○ Antimicrobial proteins such REQUIREMENTS FOR INFECTION IN THE SKIN as defensins and secretory IgA antibodies — IgA is an If the skin is compromised such important antibody for as in burns and wounds, mucosal defense. pathogens can enter the body ○ Normal flora which is through damaged skin WITHOUT particularly evident in the substantial effort. colon. Compromised Survive the Therefore, pathogens that affect A practical example is excessive skin harsh the GIT require strategies to physical exfoliation of the face. ○ Physical exfoliation can conditions of resist acidic pH or else they will cause breaks in the skin GIT die. where bacteria can enter, Infections can occur if there is: causing breakouts. ○ Decreased gastric acid output ○ There are organisms If the pathogen can penetrate an Damaged intact capable of surviving in acidic intact skin is such as Schistosoma skin environments. larva (cercaria). Shigella: has genes that confer acid resistance Thrive in the Giardia and Fungi (dermatophytes). keratinous Entamoeba: cyst Infection can also occur in the layer of the formation setting of an intact skin. skin Cysts can survive adverse B. GASTROINTESTINAL TRACT environmental In order to establish infection should fulfill the following conditions conditions. Once the environmental conditions are REQUIREMENTS FOR INFECTION IN THE GIT favorable, an example is when Enter and exit Route of transmission of most they already reach the GIT GIT pathogens. the intestine, they Pathology - Mod 5 Transmission and Dissemination of Microbes 1 of 5 The use of trans, practice questions, and evals ratio must be used discreetly and social media/public exposure of the aforementioned shall be strictly prohibited.  1. HELICOBACTER PYLORI can release trophozoites, causing Classic example of a pathogen that manages to an infection. establish itself despite harsh gastric conditions. Associated with chronic gastritis, peptic ulcer disease, and gastric malignancies (e.g. gastric Have virulence carcinoma and lymphoma) factors that can Colonizes the stomach using several strategies either alter GIT H.pylori produces an enzyme called urease that splits function or urea into ammonia and carbon dioxide. damage the ○ Urease: breaks urea into ammonia (a basic GIT compound), which increases gastric pH ○ Ammonia: a basic compound which increases gastric pH, counteracting the acidity of the stomach. VIRULENCE FACTORS In time, H.pylori can also cause eventual loss of acid-producing cells in the stomach, with Usually alter physiology consequent profound increase in gastric pH, WITHOUT significant tissue furthering its survival. damage ○ Increased pH alters mucus and enables freer Cause abnormality in ionic motility of H.pylori, leading to colonization. balance ○ Consistency becomes more favorable for S. aureus exotoxin: nausea, H.pylori to move about. vomiting, diarrhea The combination of these factors causes colonization Vibrio cholerae and of the gastric epithelium. Enterotoxigenic E. coli: watery From there, H.pylori uses its other virulence factors to diarrhea cause disease in its host. Toxins ○ Cholera toxin encoded by Vibrio C. RESPIRATORY TRACT cholerae The respiratory tract is a system with a blind end, the Can alter the physiology lungs. of the colon by causing Organisms infecting the respiratory tract enter and exit increased secretion of via the same orifices, namely the nose and the mouth. chloride ions into the intestinal lumen, which clinically translates to REQUIREMENTS FOR INFECTION FOR profound watery RESPIRATORY TRACT diarrhea. Enter and exit An example of this is when an Some GIT infections present with the respiratory infected person sheds microbes by painful, bloody diarrhea called tract aerosolizing into respiratory dysentery (respiratory droplets that another person can Pathogens can invade the route) inhale (e.g., COVID-19) intestinal lining/mucosa, causing Invasion tissue damage (e.g. Shigella and Another special feature of the Entamoeba histolytica) respiratory tract is that it has a lot There will be hemorrhage when of defense mechanisms like the the blood vessels are involved, mucociliary apparatus, and presenting blood diarrhea resident phagocytes. Hijack innate For respiratory pathogens to defenses of the Hookworms (Necator and establish themselves, they must respiratory Ancylostoma): Iron-deficiency be able to hijack these defense tract anemia from chronic mechanisms to their advantage. (mucociliary gastrointestinal bleeding. ○ Mycoplasma pneumoniae apparatus, ○ These organisms hook to can produce a toxin that can phagocytes) intestinal lining and suck paralyze the mucociliary blood which stimulates apparatus. chronic gastrointestinal blood ○ Mycobacterium loss tuberculosis can resist ○ Blood loss in the gut causes phagocytosis. Extraintestinal iron deficiency anemia manifestations Diphyllobothrium latum: For This is achieved because viruses Megaloblastic anemia intracellular express surface proteins (abnormally large red blood cells) pathogens like recognizable by specific receptors from competition with the host for viruses, they in the host cell, allowing the specificity Vitamin B12. DNA synthesis will should be able seen in viruses preferentially infecting be impaired because of Vitamin to enter the certain cells, a phenomenon known B12 deficiency. target cell as tropism. Parasites with blood-lung phase (e.g., Ascaris lumbricoides): from Damaged In patients with a primary lung migration of worms to the epithelium infection, the damaged epithelium respiratory tract (previous caused by the infection enables other Pathology - Mod 5 Transmission and Dissemination of Microbes 2 of 5 The use of trans, practice questions, and evals ratio must be used discreetly and social media/public exposure of the aforementioned shall be strictly prohibited.  infection) or microbes to enter the respiratory tract Vesicoureteral reflux: facilitates impaired host with ease. ascension of infection from defenses bladder to the upper urinary tract (immunodeficie Urinary stasis or retention ncy) ○ Promotes infections due to loss of this “flush” and by serving as a medium for 1. BACTERIAL PNEUMONIA ON TOP OF COVID-19 pathogenic microbe growth. PNEUMONIA ○ Any urinary tract Explains why some COVID-19 patients need to also be obstruction can lead to treated with antibiotics (e.g., co-amoxiclav and urine stasis and subsequent azithromycin) infection. For immunocompromised patients, opportunistic Nodular prostatic hyperplasia pathogens like fungi can cause unhindered infection due in elderly males, where the to impaired host defense mechanisms. urethra passes through the prostate. 2. SARS-COV-2 Prostatic hyperplasia most Causative agent of COVID-19 commonly affects the area Can infect respiratory epithelial cells because of its viral surrounding the urethra causing surface protein—the Spike (S) protein, interacting its compression. with the ACE2 receptor found in respiratory epithelial cells. Abnormalities ACE2 receptor concentration increases as we move that facilitate Shorter urethra (in females) further downwards the respiratory tract, → there are ascending Vesicoureteral reflux: allows more ACE2 receptors in the lungs. spread to the backflow of infected urine from ○ Reason why COVID-19 primarily affects the lungs upper the bladder to the ureter until it ACE2 receptors are also found in other tissues, genitourinary reaches the kidneys. explaining why other organs are damaged in a tract COVID-19 infection, especially in severe infections. Some COVID-19 vaccines make us produce Sexual intercourse (sexual antibodies against the viral S protein, preventing it route) can cause mucosal breaks from interacting with the ACE2 receptor which prevents that microbes can exploit to enter infection. the body. Compromised Presence of sexually epithelium transmitted infection (STI) damages the epithelium and allows easier entry of other microbes to the genital tract. 2. REQUIREMENTS FOR INFECTION (NON-ANATOMIC) REQUIREMENTS FOR INFECTION FOR NON-ANATOMIC UROGENITAL TRACT The microbes that want to infect the genitourinary tract should have an anchor to hold it in Have the place in the phase of continuous SARS-CoV-2 means to flow of urine. adhere to E.g., P fimbriae of E.coli → D. UROGENITAL TRACT epithelium enables it to adhere to urothelial cells 1. REQUIREMENTS FOR INFECTION (ANATOMIC) E.coli Neisseria gonorrhoeae REQUIREMENTS FOR INFECTION FOR ANATOMIC Lactobacilli that prevents growth UROGENITAL TRACT of the pathogenic bacteria by producing lactic acid that Infections can occur when the anatomic conditions acidifies the environment. favor the growth, entry and spread of microbes. E.g., douching: cleaning the Overcome the When microbes have virulence factors, allowing vaginal canal with fluids, favoring normal flora (in them to remain within the genitourinary tract. growth of Gardnerella females) vaginalis, causing bacterial The normal flow of urine through vaginosis the genitourinary tract serves as ○ Removes the normal Urinary stasis lactobacilli causing the a continuous “flush” preventing infection. increase in the pH of the Pathology - Mod 5 Transmission and Dissemination of Microbes 3 of 5 The use of trans, practice questions, and evals ratio must be used discreetly and social media/public exposure of the aforementioned shall be strictly prohibited.  environment, allowing growth MECHANISM AND EXAMPLES OF PATHOGENS of pathogenic microbes. ENTERING THE BODY VIA VERTICAL TRANSMISSION E.g., antibiotic intake Mechanism Details/Examples E. VERTICAL TRANSMISSION Placental-fetal Rubella infection Transmission of microbes from the mother to the transmission (in utero) fetus/baby Transmission during Opthalmia neonatorum birth as the baby (suppurative conjunctivitis) 1. REQUIREMENTS FOR INFECTION passes the birth canal Neisseria gonorrhoeae Chlamydia trachomatis 1.1 Mother should have the infection. Can manifest as either systematic (pathogen is Juvenile respiratory circulated in the body) or genital (localised in the lower papillomatosis (multiple genital tract): papillomas in the respiratory tract) Human papillomavirus A systemic pathogen must cross the placenta or if the mother has a lower Postnatal transmission Cytomegalovirus (CMV) Intrauterine in maternal milk Human Immunodeficiency genital tract infection, it must cross the infections Virus (HIV) placenta or ascend to the uterus and eventually infect the fetus. Hepatitis B Virus (HBV) Active genital lesions in the lower Intrapartum genital tract and the fetus must be TORCH INFECTION infections delivered vaginally to have contact with Toxoplasmosis, others: Syphilis, HBV, Rubella, CMV, the lesions. and HSV Can be transmitted in all three ways BUT Postpartum The pathogens must be secreted into or transplacental transmission of HSV is infections present in the breast milk UNCOMMON. (breastfeeding). HSV transmission most commonly occurs because of ascending infection when the mother has been 1.2 Timing of the intrauterine infection has a baby infected, or exposure to lesions during vaginal profound delivery. ○ When there is evidence of active genital If the infection occurs during the period of infection in a patient who is about to give birth, organogenesis (3 to 9 weeks AOG), the development the preferred method of delivery is Cesarean of the organs becomes disrupted → birth defects. section for the baby to avoid contact with lesions. ○ Vaginal delivery is discouraged. CONGENITAL RUBELLA SYNDROME D. RELEASE AND TRANSMISSION OF MICROBES Rubella infection during the third trimester has little Means of release: effect on the fetus because at this time, the organs are already fully formed. The case is different if the mother contracts rubella Skin Shedding during the FIRST TRIMESTER because the baby may Respiratory Coughing, sneezing present with congenital rubella syndrome. Excreta Urine, feces Features: Intellectual disability Contact with infected tissues or Sexual Contact Cataracts secretions Deafness (sensorineural) Congenital heart defects Insect Vectors Mnemonic: 4Bs “Bobo, Bulag, Bingi, Butas ang puso” ROUTE OF TRANSMISSION Route Details/Examples Entry: inhalation of infected droplets Can either be droplet or airborne ○ Droplet: large, can travel short Respiratory distances (e.g., influenza viruses) ○ Airborne: smaller, can travel long distances (e.g., M. tuberculosis) Entry: oral (ingestion of Congenital Rubella Syndrome Fecal-Oral fecal-contaminated food or water) Pathology - Mod 5 Transmission and Dissemination of Microbes 4 of 5 The use of trans, practice questions, and evals ratio must be used discreetly and social media/public exposure of the aforementioned shall be strictly prohibited.  E.g., Hepatitis A and E virus, Polio virus, Enterobacteriaceae (E. coli, Salmonella, etc.) Prolonged intimate or mucosal Sexual contact E.g., HSV, HIV, HPV Other routes of transmission: ○ Saliva ○ Blood meals taken by insect vectors ○ Zoonotic: from animal to human (through direct contact or vector) Pathology - Mod 5 Transmission and Dissemination of Microbes 5 of 5 The use of trans, practice questions, and evals ratio must be used discreetly and social media/public exposure of the aforementioned shall be strictly prohibited.