Foundations: Infectious Disease 2 Flashcards
What is an infectious dose?
The amount of pathogen required to cause an infection in the host
What is “shedding”?
The successful reproduction, expulsion, and host-cell infection caused by virus progeny
What does PCR do?
Amplifies a single or a few copies of a piece of DNA to generate thousands to millions of copies
What does immunofluorescent assays and ELISA do?
Use an enzyme immunoassay to detect the presence of a substance (antigen)
What 3 diseases account for half of deaths due to infectious diseases?
Tuberculosis
Malaria
AIDS
How is African Trypanosomiasis spread?
By the tsetse fly spreading protozoa Trypanosoma brucei
What do parasites produce in African Trypanosomiasis?
Tryptophol
Describe symptoms that would present during the early (hemolytic) phase of African Trypanosomiasis.
Fever, headaches, arthralgia, pruritis
Parasites invade circulatory and lymphatic systems
Describe the symptoms that would present during the second (neurologic) stage of African Trypanosomiasis.
Confusion, poor coordination, disrupted sleep
Parasites invade CNS, pass thru blood brain barrier
How is Cholera spread?
Through contaminated drinking water, unsanitary conditions
What bacterium is responsible for Cholera?
Vibrio cholerae
gram-
facultative anaerobe
unipolar flagellum
What does Vibrio cholerae secrete and what does it cause?
Secretes cholera toxin which produces watery diarrhea
What symptoms would a person with Cholera present with?
Abdominal cramps watery diarrhea excessive thirst dry mucus membranes sunken eyes lack of tears
What is one of the most common causes of waterborne illness in the US?
Cryptosporidiosis enteritis
How is Cryptosporidiosis spread?
Fecal oral
parasites transmitted by microbial cysts (oocysts)
What is the incubation period of Cryptosporidiosis?
1-30 days, median of 7 days
When does Cryptosporidiosis shedding stop?
After 2 weeks
What cells are primarily affected by Cryptosporidiosis?
Intestinal epithelial cells of small intestines and proximal colon
Describe sporadic Cryptosporidiosis.
Water-related outbreaks of self-limited diarrhea in immunocompetent host
Describe chronic Cryptosporidiosis.
Life-threatening in immunocompromised patients, especially those with HIV
Describe the third main form of Cryptosporidiosis.
Diarrhea and malnutrition in young children in developing countries
Where is Cryptosporidiosis most commonly isolated?
In HIV+ patients presenting with diarrhea
What populations are at high risk of catching Cryptosporidiosis?
Animal handlers
MSM
Ppl having close contact with infected ppl
Young children
How can you diagnose Cryptosporidiosis?
Find the antibody in stool
Parasite exam with microscope
Immunofluorescent assays and ELISA to detect antigen and oocysts
How is Dengue Fever spread?
Through bites of Aedes aegypti mosquito in Asia and Africa
What symptoms would someone with Dengue Fever present with?
Abrupt fever > 40*C of 2-7 days duration
How does mild Dengue Fever present?
Usually in infants and young children
Nonspecific febrile illness
How does moderate Dengue Fever present?
In older children and adults High fever Severe HA Myalgia/arthralgia Rash
How does severe Dengue Fever present?
As Dengue hemorrhagic fever
High fever
Hemorrhaging
Circulatory failure
How would you test for Dengue Fever?
Look for the antibody (IgM or IgG)
A CBC for leukopenia and thrombocytopenia
PCR for dengue virus types
How would you treat Dengue Fever?
Get rid of standing water.
No specific treatments.
How many leukocytes would you find in a CBC for Dengue Fever?
<3500 WBCs/mL (leukopenia)
How many platelets would you find in a CBC for Dengue Fever?
<50,000 platelets/mL (thrombocytopenia)
What type of infection usually causes hepatitis?
Viral infections
Which types lead to chronic disease?
B & C
What can hepatitis commonly cause?
Liver cirrhosis
cancer
transplant
What types are typically caused by ingesting contaminated food or water?
A & E
What types are usually caused by parenteral contact with infected body fluids?
B, C & D
How is HAV spread?
Fecal-oral
Ingestion of contaminated water/food (shellfish)
Direct contact with infected person
When is the greatest infectivity of HAV?
2 weeks before onset of symptoms
How long is the incubation period for HAV?
About 28 days
Does HAV infection severity increase or decrease with age?
Increases with age
What symptoms would a person with HAV present with?
Fever dark urine malaise/fatigue jaundice distaste for smoking
What would you find during a physical exam of someone with HAV?
Hepatomegaly fever jaundice icterus hives RUQ tenderness
What population accounts for over 50% of cases in north American and Europe?
Foreign travel to developing countries
What is a normal level of Aspartate Aminotransferase (AST)?
2-4 IU/L
What is a normal level of Alanine Aminotransferase (ALT)?
2-40 IU/L
What is the normal AST:ALT?
<1
What is an AST:ALT >2:1 associated with?
Viral/alcoholic hepatitis, hepatocellular carcinoma
What is an AST:ALT 1-2 associated with?
Cirrhosis
How high could the AST:ALT get with HAV?
Could exceed 10,000
What immunoglobulins are present?
Anti-HAV IgM (onset of symptoms)
Anti-HAV IgG (soon after IgM, persists for years)
What titer would appear positive for HAV before IgM and IgG?
Fecal HAV
What do you have to do whenever someone tests positive for HAV?
Report to local public health department
What would the follow-up recommendations be for someone with HAV?
Can return to work/school 10-14 days after onset of symptoms
How would you treat HAV?
No antivirals… resolves spontaneously
What type of virus is HAV?
RNA enterovirus
member of Picornavirdae family
What type of virus is HBV?
DNA virus
member of Hepadnaviridae family
What is the most common infectious disease in the world?
HBV
What sex is affected more by HBV?
Male>Female (2:1)
How would an individual with acute HBV present?
Fever/malaise Anorexia Jaundice/icterus Dark urine/pale stools RUQ pain
How would an individual with chronic HBV present?
Asymptomatic
What would you find during a physical exam of someone with noncirrhotic chronic HBV?
Usually normal
Who should you screen and vaccinate if screen is negative?
Ppl from endemic areas IV drug users MSM HIV and HCV+ ppl Inmates of correctional facilities
What is the incubation period for HBV?
6 weeks to 6 months with insidious onset
What will be the first evidence of clinical HBV infection?
Elevated HBsAg
What does HbeAg indicate?
Viral replication and infectivity (secretory form of HBcAg during incubation period)
What is the second evidence of clinical HBV infection?
Anti-HBc (since HbcAg does not appear in the serum)
What results would indicate an acute HBV infection?
+IgM HBcAb
What results would indicate a chronic HBV infection?
-IgM
+IgG or total HBcAb
When does Anti-HBs show up?
After clearance of HBsAg and after successful vaccination against HBV
What type of virus is HCV?
RNA virus
family Flaviviridae
What ages are most prevalently affected by HCV?
Between 40-60
How does acute HCV present?
Symptoms develop about 2 weeks after exposure (rare)
How does chronic HCV present?
Mildly symptomatic (fatigue) or asymptomatic elevated ALT/AST for 2-12 weeks
What symptoms would a person with acute HCV present with?
Fever, malaise, nausea, jaundice/icterus, dark urine, RUQ pain
What percentage of acute HCV become chronic?
70-80%
What percentage of chronic HCV is curable?
~50%
What are some conditions associated with HCV?
Diabetes Metabolic syndrome Iron overload Depression Substance abuse
What would you find on a physical exam of someone with HCV?
Normal unless advanced fibrosis/cirrhosis
What lab tests can be used to test for HCV?
Test for Ab to HCV (4-10 weeks after infection)
Qualitative test for presence/absence of virus (PCR) (2-3 weeks after infection)
Why is it beneficial to catch an HCV infection early?
The earlier you catch the disease, the healthier the patient is, the better the patient can take the harsh treatment
What type of virus is HDV?
RNA virus that requires the presence of HBV
What part of HBV envelopes HDV?
A lipoprotein coat from HBsAg
What populations are at high risk for HDV infection?
HBsAg-positive prostitutes, MSM
IV drug users
How is HDV spread?
Percutaneous or mucosal contact with infectious blood
What signature symptom develops after the disappearance of typical hepatitis symptoms?
Jaundice reflects the initial acute infection
What is more likely to happen with concurrent HBV and HDV infections?
Fulminant hepatitis
progress to chronic liver disease
Who would you screen for HDV?
Patients who are HBsAg+
Patients with acute/chronic hepatitis
Patients with acute HBV
How would you diagnose HEV?
Reverse transcriptase PCR to detect the HEV RNA
Immune electron microscopy
What is Hepatitis F?
dsDNA that is different from HAV and HEV (both RNA)
What is GBV/C?
Usually patients with “hepatitis G” are infected with HBV and/or HCV
What cell is infected with HIV?
CD4+ cell
What does the HIV release into the CD4+ cell?
Viral RNA and reverse transcriptase
How long would it take for an HIV+ patient to develop AIDS without antiretroviral treatment?
About 10 years after transmission
What CD4 count defines AIDS?
<200 CD4 cells
What is the biggest risk factor for HIV infection?
Sexual activity. It accounts for 70% of world transmission.
What is the strongest predictor of heterosexual transmission?
Viral load
What is the strongest predictor of transmission risk from mother to child?
Maternal HIV-1 RNA level
Can HIV be transmitted via breast milk?
Yes
How do you treat HIV+ pregnant women?
Until viral load is undetectable
Name another risk factor for HIV infection besides sexual activity.
Recipients of blood products (1975-1985)
IV drug use
Name some conditions associated with HIV.
More aggressive Syphilis
100x greater risk for developing TB
More rapid cirrhosis in HCV
What symptoms could an HIV+ patient present with?
Similar to mononucleosis: Fever Adenopathy Pharyngitis Rash Myalgia/arthralgia
What defines acute retroviral syndrome?
Decline in CD4 lymphocytes
Increased viremia
1-4 weeks after transmission
high HIV RNA in absence of HIV Ab
What defines seroconversion?
Positive HIV Ab test within 4 weeks of acute infection and invariably by 6 months
How does acute retroviral syndrome acquired by sexual activity cause infection?
Virus enters in infected macrophages
Dendritic cells carry virus to lymph nodes
CD4+ cells become infected
