Chapter 8 Flashcards
What is the typical cause of most human infectious diseases?
Microscopic organisms are widely distributed in the environment and carry out many beneficial functions. Unfortunately, human infectious diseases are typically caused by bacteria and viruses, collectively called pathogens.
What are the three lines of defense against invasion concerning infectious diseases?
The body has three lines of defense against invasion: barriers to entry, first responders, and acquired defenses.
What type of cells are bacteria? What is a capsule? What is a plasmid?
Bacteria are single-celled prokaryotes. Bacteria have a cell wall that contains a unique amino disaccharide, and in some bacteria, a capsule that has a thick, gummy consistency is present outside of the cell wall. Many bacteria have accessory rings of DNA called plasmids that may carry antibiotic resistance. Bacteria reproduce by binary fission. Bacteria may release toxins that damage the human body.
What is a virus? What are the two parts of a virus? How do they replicate?
Viruses are acellular and obligate parasites, meaning that they must replicate inside a living cell. A virus always has two parts: an outer capsid composed of protein units and an inner core of nucleic acid, which can be either DNA or RNA. In large measure, viruses rely on the host’s enzymes and ribosomes for its own reproduction.
What is a prion? What type of diseases do they cause?
Prions, which are proteinaceous infectious particles, cause a group of degenerative diseases of the nervous system. Prions are proteins of unknown function in the brains of healthy individuals. Disease occurs when certain prion proteins change their shape into a rogue form that converts other normal prion proteins to the rogue configuration.
Define: epidemic, outbreak, pandemic.
A disease is an epidemic if there are more cases than expected in a certain area for a certain period of time. If the epidemic is confined to a local area, it is an outbreak. Global epidemics are pandemics. The CDC and the WHO monitor and respond to threats of infectious diseases.
What virus causes AIDS (acquired immunodeficiency syndrome)?
AIDS (acquired immunodeficiency syndrome) is caused by a virus known as the human immunodeficiency virus (HIV). There are two types of HIV: HIV-1 and HIV-2. HIV-1 is the more widespread and virulent form; HIV-2 corresponds to a type of immunodeficiency virus found in the green monkey of western Africa.
What is an opportunistic infection?
AIDS is the advanced stage of HIV infection, in which a person develops one or more of a number of opportunistic infections. An opportunistic infection is one that has the opportunity to occur only because the immune system is severely weakened.
Where did the HIV virus originate? Why is AIDS considered a pandemic?
Origin of and Prevalence of HIV
It is generally accepted that HIV originated in Africa. AIDS is a pandemic because the disease is prevalent in the entire human population around the globe. As of 2014, an estimated 36.9 million people were living with HIV infection. In 2014, the disease claimed 1.2 million lives. A few of the hardest-hit regions include sub-Saharan Africa, India, South Africa, Latin America, and the Caribbean.
What cells of the immune system are infected by HIV? What is one of the most common causes of death in the United States of people who have AIDS?
HIV-1B causes most HIV infections in the United States. HIV infects helper T cells and macrophages that are called CD4 cells because they display a molecule called CD4 on their surface. In 1993, the CDC issued clinical guidelines for the classification of HIV to help clinicians track the status, progression, and phases of HIV infection. In the United States, one of the most common causes of AIDS deaths is from Pneumocystis jiroveci pneumonia (PJP).
For each of the following phases of HIV infection, note the symptoms and the CD4 T-cell count.
a) Category A: Acute Phase
b) Category B: Chronic Phase
c) Category C: AIDS
Category A: Acute Phase
A person in category A typically has no apparent symptoms, is highly infectious, and has a CD4 T-cell count that has never fallen below 500 cells per mm3 of blood, compared to the normal T-cell count of 800 cells/mm3. Initially, an HIV antibody test is usually negative, but after a period of time, the body responds to the infection by making antibodies against HIV, and the HIV test becomes positive.
Category B: Chronic Phase
A person in category B would have a CD4 T-cell count between 499 and 200 cells/mm3 and one or more of a variety of symptoms related to an impaired immune system, such as a yeast infection or prolonged diarrhea.
Category C: AIDS
When a person has AIDS, the CD4 T-cell count has fallen below 200 cells/mm3 or the person has developed one or more of the 25 AIDS-defining illnesses (opportunistic infections) such as Kaposi sarcoma, Pneumocystis jiroveci pneumonia, toxoplasmic encephalitis, Mycobacterium tuberculosis, or invasive cervical cancer. There is still no cure for AIDS, but many people with HIV infection are living longer, healthier lives due to antiretroviral therapy.
What type of virus is HIV?
HIV consists of two single strands of RNA, various proteins, and an envelope. Within the matrix, there are three very important enzymes: reverse transcriptase, which catalyzes reverse transcription; integrase, which catalyzes the integration of viral DNA into host cell DNA; and protease, which catalyzes the breakdown of new viral polypeptides into viral proteins. A retrovirus must use reverse transcription to convert its RNA into viral DNA.
What are the methods of transmission of HIV?
HIV is transmitted by sexual contact with an infected person, including vaginal or rectal intercourse and oral/genital contact. Also, needle sharing among intravenous drug users is high-risk behavior. A less common mode of transmission is through transfusions of infected blood or blood-clotting factors. Babies born to HIV-infected women may become infected before or during birth or through breastfeeding. HIV is not transmitted through casual contact.
What does an HIV test detect?
Generally, an HIV test does not test for the virus itself. Instead, initial HIV tests are designed to detect the presence of HIV antibodies in the body.
What is the cause of tuberculosis? What are tubercles? What are the symptoms of TB? How long does it take to treat tuberculosis?
Causative Agent and Transmission
Tuberculosis is caused by the bacterium Mycobacterium tuberculosis and spread in airborne droplets, which can remain infectious for several hours.
Disease
The bacteria travel to the lungs, where they are consumed by macrophages and walled off into small, hard nodules called tubercles. Symptoms of active TB may include cough and chest pain.
Treatment and Prevention
Health experts advise control of TB by identifying and treating all known cases. The most common drugs are isoniazid, rifampin, ethambutol, and pyrazinamide. The duration of treatment is long because it takes at least six months to kill all of the bacteria in the body. Multidrug-resistant strains have also been identified. Public health officials try to identify and treat all cases of active TB.
