patoloji-ders-notlari

Title

Serdar Balcı

Transmission and Dissemination of Microbes

Serdar BALCI, MD

How microbes enter body?

Microbes enter the body if they overcome the natural barriers and defense mechanisms

Natural barriers

Intact Skin

Mucosa

Blood Brain Barrier

Natural barriers are physical barriers and produce antimicrobial substances

Defense mechanisms

Saliva

Tear

sIgA

Peyer’s patches

Routes of Entry of Microbes

Breaches in the skin

Inhalation

Ingestion

Sexual transmission

Infections occur in otherwise healthy persons

SKIN

Skin

Microorganisms penetrate through breaks in the skin

Superficial pricks → fungal infections

Wounds → staphylococci

Burns → Pseudomonas aeruginosa

Diabetic and pressure-related foot sores → multibacterial infections

From secretions of dead body → Ebola

Intravenous catheters in hospitalized patients → local or systemic infection

Needle sticks → HBV, HCV, HIV

Farklı isimlendirmek gerekirse

Çorum-Yozgat Kanamalı Ateşi

Animal bites

Bacteria or certain viruses

Rabies

Microorganisms penetrate through intact skin

GASTROINTESTINAL TRACT

Gastrointestinal Tract

Food or drink contaminated with fecal material

Natural disasters (floods, earthquakes), diarrheal diseases

Acidic gastric secretions

Other defense mechanisms of GI

Viscous mucus layer covering the intestinal epithelium

Lytic pancreatic enzymes and bile detergents

Mucosal antimicrobial peptides called defensins

Normal flora

Secreted IgA antibodies

Peristalsis

Mucosa-associated lymphoid tissue (MALT)

When does infection occur?

Viruses

Enteropathogenic bacteria

Fungal infections in GI tract

Intestinal protozoa

Color Atlas Of Pathology

Color Atlas Of Pathology

Intestinal helminths

RESPIRATORY TRACT

Microbes are inhaled in dust or aerosol particles

Viruses

Impaired Ciliary Acitivity

Damage to ciliary activity

M. tuberculosis

Avoid phagocytosis

Avoid destruction after phagocytosis

Escapes killing within the phagolysosomes of macrophages

Opportunistic fungi

UROGENITAL TRACT

Urinary Tract Infections

UT is invaded from the exterior by way of the urethra

Flushing of the urinary tract with urine serves as a defense against invading microorganisms

Urine in the bladder is normally sterile

N. gonorrhoeae, E. coli adhere to the urinary epithelium

Anatomy is important in UT infection

Urinary tract infections

Vagina has normal flora

Low pH

Catabolism of glycogen in the normal epithelium by lactobacilli

Normal under estrogen

Antibiotics kill the lactobacilli → Overgrowth of yeast → Vaginal candidiasis

Vertical Transmission

SPREAD AND DISSEMINATION OF MICROBES WITHIN THE BODY

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Microorganisms proliferate locally, at the site of initial infection

Penetrate the epithelial barrier and spread to distant sites by way of the lymphatics, the blood, or nerves

Secrete lytic enzymes which destroy tissue and allow direct invasion

Invasive microbes initially follow tissue planes of least resistance and drain to regional lymphatics

Microorganisms spread in the blood or lymph either free in extracellular fluid or within host cells

Blood cells carry microbes

Virus transmission

Infectious foci seeded by blood

Bloodstream

Manifestations appear distant from the point of microbe entry

RELEASE FROM THE BODY AND TRANSMISSION OF MICROBES

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Transmission depends on the hardiness of the microbe.

**Bacterial spores, protozoan cysts, and thick-shelled helminth eggs can survive in a cool and dry environment. **

Less hardy microorganisms must be quickly passed from person to person, often by direct contact.

Desquamated Skin

S. aureus, dermatophyte fungi are shed in the desquamated skin

Saliva

Saliva include mumps virus, cytomegalovirus, and rabies virus

Respiratory secretions

Stool

Shigella, Giardia lamblia, rotavirus

Pathogens that replicate in the liver (hepatitis A virus) or gallbladder (Salmonella serotype typhi) enter the intestine in bile and are shed in stool

Hepatitis A, E, Poliovirus, Rotavirus in epidemic outbreaks

Parasite eggs

Blood

Urine

Schistosoma haematobium

Sexually transmitted infections

Urethra, vagina, cervix, rectum, or oral pharynx

Direct contact for person-to-person spread

Do not survive in the environment

Asymptomatic people who do not realize that they are infected

Infection with one STI increases the risk for additional STIs

Robbins and Cotran’s Pathological Basis of Diseases

Mother to Baby

Zoonotic infections

Animal to human

Direct contact

Consumption of animal products

Indirectly by an invertebrate vector

Nosocomial Infections

References

Robbins Basic Pathology 9 th __ Ed, pp: 315-319__

Robbins and Cotran’s Pathological Basis of Disease 8th Ed, pp: 338-342

Color Atlas of Pathology, pp: 268-285