Question

45. Describe the differences between how Shigella and Salmonella cause infection and diarrhea.

46. Distinguish between a vesicular and macular rash and name 2 organisms that cause each of the types of rashes.

47. identify what the H and N markers of influenza are and explain how they help the virus survive. Why was the 1918 flu so dangerous?

48. Outline and describe the steps of Mycobacterium tuberculosis infection.

49. What two diseases are caused by Salmonella? What are the symptoms and the treatment of each type?

50. What are the symptoms of the primary stage, secondary stage, and tertiary stage of syphilis? How is it treated?

Answer 1

45. Both Shigella and Salmonella are gram negative , facultative, spore forming anaerobic organisms.

Difference between Salmonella and Shigella infection are:

Salmonella affects both large and small intestines while Shigella mainly affects the large intestine.

Salmonella produces enterotoxin while Shigella produces heat labile toxin referred to as Shiga toxin.

Salmonella is transmitted through raw food, contaminated food and water while Shigella is transmitted through person to person contact.

46. When a rash appears in the same place as multiple vesicles, it's known as a vesicular rash. Heat rashes are one type of vesicular rash, occurring mainly in folds of the skin or wherever clothing can cause friction .eg: systemic vesicular rash is chickenpox, whereas local vesicular rashes caused by herpes zoster, vesicular rashes can occur in children with impetigo caused by staphylococcal skin infection in the summer

A maculopapular rash is a type of rash characterized by a flat, red area on the skin that is covered with small confluent bumps. eg : hand foot and mouth disease in children caused by Coxsackievirus A16, Measles caused by rubeola virus

47. Influenza A viruses are divided into subtypes based on two proteins on the surface of the virus: hemagglutinin (H) and neuraminidase (N). Hemagglutinin and neuraminidase protein spikes on the flu virus  surface help them invade host cells.

The 1918 influenza pandemic was the most severe pandemic in recent history. It was caused by an H1N1 virus with genes of avian origin. It is estimated that about 500 million people or one-third of the world’s population became infected with this virus. The number of deaths was estimated to be at least 50 million worldwide with about 675,000 occurring in the United States. Mortality was high in people younger than 5 years old, 20-40 years old, and 65 years and older. The high mortality in healthy people, including those in the 20-40 year age group, was a unique feature of this pandemic.At the time, there were no effective drugs or vaccines to treat this killer flu strain. Citizens were ordered to wear masks, schools, theaters and businesses were shuttered and bodies piled up in makeshift morgues before the virus ended its deadly global march.

48. TB infection happens in 4 stages: the initial macrophage response, the growth stage, the immune control stage, and the lung cavitation stage.

The initial macrophage response: In this stage during the first week after the inhalation of the TB bacillus , the bacillus enters into the alveoli of lungs. Here it gets picked up by special cells of the immune system, called macrophages. The macrophages swallow the TB bacillus.  If the amount of TB bacilli is too large, or if the macrophage is not strong enough to resist, the bacilli can reproduce in the macrophage. This ultimately leads to the destruction of the macrophage and the infection of new, nearby macrophages.

The growth stage : If the macrophages fail to tackle the infection TB bacillus then  bacilli start reproducing exponentially. This leads to a rapid expansion of the intial TB bacillus, and the macrophages cannot contain the spread anymore. This stage lasts until the third week after initial infection.

Immune control stage :  the bacilli do not grow exponentially anymore, it seems that at that stage, bacilli growth and destruction by macrophages are balanced. The body brings in more immune cells to stabilize the site, and the infection is under control.TB bacilli and macrophages that swallowed them build a round complex called Ghon complex in the lungs.  TB bacilli are shielded from the lung tissue but the patient will be not contagious because the bacilli cannot enter the airway and will not come out by coughing or sneezing. In some cases if the immune system is strong the complex gets healed

The lung caviation stage: the primary complex does not heal and the TB bacilli become re-activated after a period of 12 to 24 months after the initial infection. TB bacilli reproduce quickly and form a cavity in the tissue, where the body’s immune system cannot reach them. Here TB bacilli quickly spread through the tissue and the person develops signs and symptoms of active TB such as coughing. In this stage, the person is highly contagious because his or her sputum contains active TB bacteria.