Picornaviridae

• Causes at least 50% of colds
• Causes bronchitis
• Spreads by nasal/oral transmission

Coronaviridae

• Causes 20% of colds
• Causes bronchitis
• Spread by nasal/oral transmission

G+ coccus

Facultative Anaerobe

• Causes streptococcus pharyngitis, laryngitis, tracheitis, sinusitis, and Otitis media
• Produces many exotoxins and enzymes (streptolysins)
• Can spread causing rheumatic fever and rheumatic heart disease

Herpesviridae

• largest human herpesvirus
• Causes CMV infection (pharyngitis)
• Acquired from most bodily secretions and blood
• Transmitted by salivary glands
• Persistent and latent infection: remains latent in neutrophils, T-cells, monocytes
• Often asymptomatic but can spread to lymphoid tissue (agranulocytes in spleen, lymph nodes) --> then salivary glands, kidneys, reproductive organs
• Dangerous for babies and the immune impaired

Herpesviridae

• Can induce cancer (Hodgkin's Disease)
• Replicates in B-cells
• Virus is shed in saliva from infected salivary glands and oropharynx epithelial cells --> spreads to B-cells in lymphoid tissue
• T-cells respond to infected B-cells and become hyperplastic
• Infectious mononucleosis --> fever, anorexia, lethargy, splenic rupture

• Causes parotitis, sinusitis (RSV), otitis media (RSV),
• Typically airborne or salivary secretion transmission
• Lytic infection
• Life-long resistance to reinfection

G- bacillus

Aerobic

• Causes Otitis externa (swimmer's ear)
• produces both exo- and endotoxins

G+ diplococcus

Facultative anaerobe

• Causes Otitis media, sinusitis, laryngitis, tracheitis, and typical pneumonia

G- bacillus

Facultative anaerobe

• Causes Otitis media, sinusitis, epiglottitis

Paramyxoviridae

• Causes Otitis media, sinusitis, bronchiolitis, pneumonia
• Most common cause of bronchiolitis and pneumonia in children under 2
• It inflames the bronchioles and restricts air to alveoli
• During replication of the virus, expression of the fusion protein at the cell membrane can result in the fusion of neighboring cells and the formation of multi-nucleate cells (syncytia)

• Lacks a cell wall and instead has a cell membrane that incorporates sterol compounds (like eukaryotes)
• Aerobic
• Causes atypical pneumonia (walking pneumonia)

Orthomyxoviridae

• Causes pandemic, epidemic, and endemic influenza
• Causes bronchitis
• Fever, myalgia, headache, pharyngitis
• Contains H spikes (recognition and attachment) and N spikes (exit)

G- coccobacillus

Aerobic

• Causes "whooping cough" (pertussis)
• Attaches to and multiplies in ciliated tracheal cells but don't invade deeper
• Major cause of death worldwise

G+ bacillus

Aerobic

• Waxy outer coat
• Grows slowly and in clumps

• A dimorphic fungus that exhibits yeast-like growth in tissues and filamentous in soil
• Causes histoplasmosis: inhaled Histoplasma capsulatum spores that results in lesions in the lungs and can spread via blood and lymphatics
• Found in feces of startlings, pigeons, chickens, bats and in soil with high nitrogen content
• Usually asymptomatic

G- bacillus

Facultative anaerobe

• Normal gut inhabitant
• Endotoxin (all strains); enterotoxins associated with diarrhea
• 5 different groups associated with gastroenteritis: enterohemorrhagic, -invasive, -pathogenic, -toxigenic, and -aggregative

G- bacillus, comma shaped

Microaerophilic

• Found in contaminated food and milk
• Animal reservoirs
• Bloody stool due to damage of the mucosal surface of the jejunum
• Most common cause of bacterial gastroenteritis

G- bacillus

Facultative anaerobe

• Causes salmonellosis
• Most common cause of food-borne diarrhea in most developed countries
• Humans acquire from poultry, meat, eggs, milk
• Usually an acute infection and self-limiting except in the young or old

G- bacillus

Facultative anaerobe

• Causes cholera
• Releases virulence factors such as an enterotoxin
• Strictly a human pathogen

G- bacillus

Facultative anaerobe

• 4 species cause bacillary dysentery (shigellosis)
• Invades ileum, colon epithelial cells; rarely invades bloodstrem
• Releases an exotoxin (Shiga toxin)
• Usually transmitted via poor sanitation, overcrowding

• Causes viral diarrhea
• Attaches to intestinal epithelium, damages transport mechanisms in the intestines
• Fecal/oral transmission

G+ coccus

Facultative anaerobe

• Causes food poisoning
• Enterotoxins act as superantigens binding to MHC, causing T-cell stimulation
• Heating can kill bacteria, however toxins are not destroyed

G+ bacillus

Anaerobe

• Causes food poisoning
• Common pathogen in birds, mammals; soil is natural habitat
• 3 types: foodborne (botulinum toxin), infant, and wound
• Site of action for toxin is the nerve synapses --> prevents release of ACh

G- spiral

Microaerophilic

• Involved in majority of gastric and duodenal ulcers
• Adhesins, urease, cytotoxins disrupt stomach and SI mucosa

G- bacillus

Facultative anaerobe

• Causes typhoid (enteric) fever
• pathogen not found in animals; only spread by human fecal/oral route
• pathogens multiply in phagocytic cells, spread to liver, spleen, and lyse becoming blood-borne

Picornaviridae

Hepatovirus

• Spread by fecally contaminated food, water, hands, or by anal intercourse
• Multiplies in the intestinal epithelium, spreads to liver, kidneys, spleen
• Usually no liver damage

Protozoan

• Causes amoebic dysentery or amoebiasis: milkd to severe diarrhea, with blood, mucus, pus in stools
• Food or water contaminated with cysts; stomach acids don't affect cysts

Protozoan

• Like Entamoeba, mild to severe diarrhea and cysts and trophozoite forms
• Adhere to microvilli of SI

Helminth

Roundworm

• Spread via fecal/oral route
• Adult worms migrate out of intestines and into lungs
• Usually not severe but can cause duct blockage

Helminth

Hookworm

• Attaches to intestinal wall, feeding on blood, tissue, and can cause anemia
• Penetrates through skin to infect the host

Helminth

Pinworm

• Migrates out of anus to lay eggs; if ingested, larvae hatch in SI
• Most common helminth infection in the US

Helminth

Cestodes (tapeworms)

• 3 stages: adult worm in intestines of humans lays eggs and are excreted in the feces, eggs ingested by grazers and hatch into larvae, humans eat undercooked meat and larvae develop into adults that attach to walls of the SI

Fungus

• A common mold
• produces a mycotoxin (aflatoxin)
• Grows on many foods, particularly peanuts and corn
• May contribute to liver cancer and cirrhosis