Infectious Disease Lecture Notes

Flashcards covering the etiology, epidemiology, pathogenesis, and clinical features of various infectious diseases including viral hepatitis, shigellosis, salmonellosis, cholera, typhoid fever, and botulism.

Hepatitis A virus (HAV)

A picornavirus of the enterovirus group, characterized as an ssRNA virus of approximately $27\,nm$, which is sensitive to boiling, chloramine, formalin, and UV light.

Fecal–oral transmission

The mechanism of transmission for Hepatitis A and E, involving the ingestion of contaminated food, water, or direct contact.

Icteric period of Hepatitis A

A clinical stage lasting about $2$ weeks characterized by the development of jaundice, hepatomegaly, increased $ALT$ and $AST$ ($3-7\times$), and a de Ritis index of $<1$.

HBsAg

The earliest serological marker for Hepatitis B infection that persists in chronic cases.

HBeAg

A marker indicating active replication of the Hepatitis B virus and high infectivity.

Direct-acting antivirals (DAAs)

Current treatment agents for Hepatitis C, including medications such as sofosbuvir, ledipasvir, and daclatasvir.

Hepatitis D virus (HDV)

A defective RNA virus that requires the presence of Hepatitis B ($HBsAg$) for replication.

Hepatitis E virus (HEV)

An RNA virus structurally similar to caliciviruses that causes more severe illness in pregnant women, especially with high mortality in the $3^{rd}$ trimester.

Shigellosis

An infection caused by Shigella spp. (Gram-negative, non-motile rods) that invades the colonic mucosa, leading to epithelial damage and ulcers.

Rectal spit

A term describing frequent loose stools containing only mucus and blood, characteristic of the height of shigellosis.

Tenesmus

Frequent, painful, and ineffective urges to defecate, commonly seen in the acute stage of shigellosis.

Salmonellosis stool characteristics

Watery, fetid, and greenish stools, often described as having a "swampy" appearance.

Typhoid-like salmonellosis

A generalized form of salmonellosis characterized by prolonged fever, intoxication, relative bradycardia, and potentially a roseolar rash.

Vibrio cholerae

A Gram-negative, curved, motile rod that produces cholera enterotoxin, which increases $cAMP$ to cause massive secretion of water and electrolytes.

Rice-water stools

The characteristic profuse, watery, non-feculent diarrhea associated with the dehydration stage of cholera.

Pokrovsky IV degree dehydration

A severe state in cholera featuring body weight loss of $\ge 10\%$, leading to algid state, coma, anuria, and collapse.

Salmonella typhi

A Gram-negative, motile rod that produces endotoxin and causes hyperplasia and necrosis in the Peyer’s patches and solitary follicles of the small intestine.

Step-ladder fever

The characteristic gradual rise in temperature seen during the initial week of typhoid fever.

Roseolar rash

A skin manifestation consisting of small rose-colored spots appearing on the abdomen or chest during the $7-10^{th}$ day of typhoid fever.

Widal reaction

A serological test used to detect $O$ and $H$ agglutinins against Salmonella typhi and paratyphi.

Clostridium botulinum

An anaerobic, spore-forming, Gram-positive bacillus that produces a neurotoxin blocking acetylcholine release at the neuromuscular junction.

Bezredko’s method

A technique for administering antibotulinic serum by giving a small test dose ($0.1\,ml$ diluted) followed by a slightly larger dose after $30$ minutes before giving the full therapeutic dose.

Oral Rehydration Solution (ORS)

A WHO standard solution containing glucose, $NaCl$, $KCl$, and sodium citrate used to treat dehydration in intestinal infections.

Relative bradycardia

A clinical sign in typhoid fever where the heart rate is slower than expected relative to the patient's elevated body temperature.