chapter 14-17 analysis + clinical applications

Ten years before Robert Koch published his work on anthrax, Anton De Bary showed that potato blight was caused by the alga Phytophthora infestans. Why do you suppose we use Koch’s postulates instead of something called “De Bary’s postulates”?

Because Robert Koch developed a procedure for being able to determine if a specific microorganism caused a specific disease and de Bary simply found that P. infestans causes potato blight and didn't come up with a method for determining causes of infection.

Florence Nightingale gathered the following data in 1855.

Discuss how Nightingale used the three basic types of epidemiological investigation. The contagious diseases were primarily cholera and typhus; how are these diseases transmitted and prevented?

-Nightingale used descriptive epidemiology when she collected the data and analyzed it.

-She used analytical epidemiology when she compared disease rates of the soldiers in the Crimean War with soldiers in England and Englishmen in the general population who were not exposed to the same diseases.

-used experimental epidemiology when she designed controlled experiments to test her hypothesis that certain diseases in soldiers were caused by a lack of basic sanitation and hygiene. She implemented changes in sanitation and observed how these changes affected the disease rates.

Name the method of transmission of each of the following diseases:

malaria

Vector-borne transmission (bite of infected Anopheles mosquitoes)

Name the method of transmission of each of the following diseases:

Tuberculosis

Airborne transmission (inhalation of respiratory droplets containing Mycobacterium tuberculosis)

Name the method of transmission of each of the following diseases:

Salmonellosis

Fecal-oral transmission (ingestion of contaminated food or water, or contact with infected animals)

Name the method of transmission of each of the following diseases:

Streptococcal pharyngitis (strep throat)

Droplet transmission (respiratory droplets from coughing or sneezing)

Name the method of transmission of each of the following diseases:

Mononucleosis

Direct contact transmission (saliva, e.g., through kissing or sharing drinks; caused by Epstein-Barr virus)

Name the method of transmission of each of the following diseases:

Measles

Airborne transmission (inhalation of virus-containing droplets or particles)

Name the method of transmission of each of the following diseases:

Hepatitis A

Fecal-oral transmission (ingestion of contaminated food or water)

Name the method of transmission of each of the following diseases:

Tetanus

Indirect contact transmission (entry of Clostridium tetani spores through wounds or punctures)

Name the method of transmission of each of the following diseases:

Hepatitis B

Bloodborne and sexual transmission (contact with infected blood, sexual fluids, or from mother to child at birth)

Three days before a nurse developed meningococcemia, she assisted with intubation of a patient with a N. meningitidis infection. Of the 24 medical personnel involved, only this nurse became ill. The nurse recalled that she was exposed to nasopharyngeal secretions and did not receive antibiotic prophylaxis. What two mistakes did the nurse make? How is meningitis transmitted?

Her first mistake was made by probably not wearing a mask. The second mistake was made by exposing herself to the nasopharyngeal secretions and not receiving any by anabiotic prophylaxis. Meningitis is the bacterial disease that can be transmitted through nasal and oral secretions -like coughing and sneezing. It is not highly contagious.

Three patients in a large hospital acquired infections of Burkholderia cepacia during their stay. All three patients received cryoprecipitate, which is prepared from blood that has been frozen in a standard plastic blood transfer pack. The transfer pack is then placed in a water bath to thaw. What is the probable origin of the infections? What characteristics of Burkholderia would allow it to be involved in this type of infection?

Probable origin of infection: contaminated transfer pack that would've activated the bacteria upon thawing or contaminated water bath.

Burkholderia is a bacteria whose natural habitats are river sediments and moist areas of soil around the roots of plants. It is one of the most adaptable of all bacteria and has an uncanny ability to survive and hostile environments, including disinfectants. Soil contains many natural antibiotics to which B. Cepacia has become resistant to the extent that it can even use penicillin as a nutrient. It rarely causes infection in healthy people but infections can occur in immunocompromised patients who do not have cystic fibrosis.

Following is a case history of a 49-year-old man. Identify each period in the pattern of disease that he experienced. On February 7, he handled a parakeet with a respiratory illness. On March 9, he experienced intense pain in his legs, followed by severe chills and headaches. On March 16, he had chest pains, cough, and diarrhea, and his temperature was 40°C. Appropriate antibiotics were administered on March 17, and his fever subsided within 12 hours. He continued taking antibiotics for 14 days. (Note: The disease is psittacosis. Can you find the etiology?)

Feb 7- March 9: incubation period

March 9: prodromal period

March 10-March 17 period of illness

March 17: period of decline by crisis

Next 2 weeks: period of convalescence

Pstittacosis is caused by chlamydophilia pstittaci

Mycobacterium avium complex bacteria are prevalent in immunocompromised and older patients. In an effort to determine the source of this infection, hospital water systems were sampled. The water contained chlorine

What is the usual method of transmission for Mycobacterium? 

What is a probable source of infection in hospitals? How can such healthcare-associated infections be prevented?

Transmission is through inhalation, ingestion, or inoculation via the respiratory or gastrointestinal tract.

Probable sources that the hospital water system has contaminated: Showerheads, tubs, sinks, etc where water can be aerosolized and inhaled.

Can be prevented by cleaning and disinfecting all sources of water

The following graph shows confirmed cases of enteropathogenic E. coli. Why is the incidence seasonal?

- it seems to have subsided as the season changed from fall to winter and to early spring

- we can assume that the results were more accurate than the samples in Jan = error factor

- bacterial level gradually increased from Jan to July = highest level and then gradually decreased to Sept

- through the seasons the overall levels of E.coli decreased

The cyanobacterium Microcystis aeruginosa produces a peptide that is toxic to humans. According to the following graph, during what season is this bacterium most toxic?

high light intensity or warmer months of summer

When Salmonella Typhimurium is injected into rats, the 1D50  is 10^6  cells. If sulfonamides are injected with the salmonellae, the ID50  is 35 cells. Explain the change in ID50  value

ID50: infectious dose (Virulence)

LD50: lethal dose (Potency)

SULFONAMIDES: antimicrobial drug (bact. only)
- The ID50 is much lower when injected with Sulfonamides 35 cells x 1000000 cells. Salmonella is part of the normal flora while Sulfonamides is not, and it end up changing the normal microbiota.

On July 8, a woman was given an antibiotic for presumptive sinusitis. However, over the next  the sinusitis worsened and was accompanied by severe pain and tightness of the jaw. On July 12, the patient was admitted to a hospital with severe facial spasms. She reported that on July 5 she had incurred a puncture wound at the base of her big toe; she cleaned the wound but did not seek medical attention. What caused her symptoms? Was her condition due to an infection or an intoxication? Can she transmit this condition to another person?

tight jaw -> puncture toe -> no treatment = Tetanus

- Tetanus, due to punctured wound that was not medically treated.

- Intoxication, definition: toxin without bacterial growth. The bacteria stay localized while its toxin can travel and spread in the body.

- Tetanus can not be transmitted from person to person, only if bacterium Clostridium tetani get into open wounds.

Explain whether each of the following examples is a food infection or intoxication. What is the probable etiological agent in each case?

Eighty-two people in Louisiana developed diarrhea, nausea, headache, and fever from 4 hours  to  2 days after eating shrimp

a) Food infection (days for symptoms to show), caused by Diatom poison

Explain whether each of the following examples is a food infection or intoxication. What is the probable etiological agent in each case?

Two people in Vermont developed malaise, nausea, blurred vision, breathing difficulty, and numbness 3  to 6 hours after eating barracuda caught in Florida.

Food intoxication (quicker, symptoms in hours), caused by Dinoflagellates which poison cause the Red Tide.

Cancer patients undergoing chemotherapy are normally more susceptible to infections. However, a patient receiving an antitumor drug that affects eukaryotic cytoskeletons was resistant to Salmonella. Provide a possible mechanism for the resistance.

Salmonella affects host cells by disrupting the plasma membrane with invasins; it then uses the host's cytoskeleton to cause further damage in the cell; the drug could disrupt one of these processes, or it could simply inhibit the division of salmonella cells

What role does transferrin play in fighting an infection?

Transferrin plays a key role in fighting infection by sequestering iron, an essential nutrient for many pathogens. By binding to iron, transferrin prevents bacteria and fungi from using this nutrient, thus limiting their growth and survival

A variety of drugs with the ability to reduce inflammation are available. Comment on the danger of misuse of these anti-inflammatory drugs.

The inflammatory response is usually beneficial in protecting the host when it is functioning appropriately.

Anti-inflammatory drugs could prevent these normal beneficial functions and make the host more susceptible to infectious diseases and cancer.

People with Enterovirus rhinovirus infections of the nose and throat have an 80-fold increase in kinins and no increase in histamine. What symptoms might you anticipate for rhinoviral infections? What disease is caused by rhinoviruses?

The increases in kinins results in vasodilation & increased permeability of blood vessels. Sx should include increased secretions from nose & eyes, sore throat, nasal congestion, sneezing, & coughing. Rhinoviruses cause the common cold

A hematologist often performs a differential white blood cell count on a blood sample. Why are these numbers important? What do you think a hematologist would find in a differential white blood cell count of a patient with mononucleosis? With neutropenia? With eosinophilia?

Differential blood count is a snap shot of ones immune system. With mononucleosis we would expect a drop on the number of B cells in the first phase of the infection. Neutropenia or low number of neutrophils results in susceptibility to infection. Neutrophils are the first line of defense in the immune response. Eosinophilia, increased eosinophils usually indicate allergy or parasitic infection.

Leukocyte adherence deficiency (LAD) is an inherited disease resulting in the inability of neutrophils to recognize C3b-bound microorganisms. What are the most likely consequences of LAD?

LAD leukocytes can't recognize opsonized Microorganisms, which delays the elimination of the microorganism by innate response and increases the susceptibility to infection

The neutrophils of individuals with Chédiak-Higashi syndrome (CHS) have fewer than normal chemotactic receptors and lysosomes that spontaneously rupture. What are the consequences of CHS?

an exhibition of hypopigmentation of the skin, eyes & hair; prolonged bleeding times; easy bruisability; recurrent infections; abnormal NK cell function & peripheral neuropathy

About 4%  of the human population have a mannose-binding lectin deficiency. How might this deficiency affect a person?

Mannose-binding lectin (MBL) helps the immune system fight infections by recognizing harmful microbes. If someone has an MBL deficiency, they may get sick more often—especially with colds, lung infections, or other common illnesses—because their immune system has a harder time spotting and attacking germs.

Injections of CTLs completely removed all hepatitis B viruses from infected mice, but they killed only 5% of the infected liver cells. Explain how CTLs cured the mice.

TC cells become CTLs, which kill infected or foreign cells. CTLs, guided by dendritic cells, cured infected mice.

Why is dietary protein deficiency associated with increased susceptibility to infections?

Not getting enough protein in your diet weakens your immune system because it reduces the production of immune cells and antibodies, making you more likely to get infections.

A positive tuberculin skin test shows cellular immunity to Mycobacterium tuberculosis. How could a person acquire this immunity?

If you have tuberculosis, your body's T cells fight it. CD4 cells activate immune responses, while CD8 cells become killers, destroying infected cells.

On a vacation to Australia, Riley was bitten by a poisonous sea snake. Quickly transported to a nearby emergency department, Riley received an antivenin injection and survived. What is antivenin? How is it obtained? How did it lead to Riley’s survival?

Antivenin is antitoxin made as a response to the venom of the sea snake. The venom is used to form antitoxins, a response by an organism.

A patient had life-threatening salmonellosis that was successfully treated with anti-Salmonella. Why did this treatment work, when antibiotics and the patient’s own immune system failed?

the antigen( pathogen) was able to escape the innate immunity and had resistance to the antibiotics, but when her adaptive immunity recognized the pathogen, it was able to kill it

A patient with AIDS has a low TH cell count. Why does this patient have trouble making antibodies? How does this patient make any antibodies?

AIDS patients with low TH2 cells struggle to make antibodies. They can still produce antibodies using certain antigens that directly stimulate B cells, bypassing the need for TH2 cells.

The secretions of a patient with chronic diarrhea were found to lack IgA, although the patient had a normal level of serum IgA. What was this patient found to be unable to produce?

The patient lacks secretory IgA, the best at fighting infections. It's like a double-sided sticker made in mucous membranes.