Following invasion, successful multiplication of the pathogen leads to infection. Infections can be described as local, focal, or systemic, depending on the extent of the infection. A local infection is confined to a small area of the body, typically near the portal of entry. For example, a hair follicle infected by Staphylococcus aureus infection may result in a boil around the site of infection, but the bacterium is largely contained to this small location.
Other examples of local infections that involve more extensive tissue involvement include urinary tract infections confined to the bladder or pneumonia confined to the lungs.
In a focal infection , a localized pathogen, or the toxins it produces, can spread to a secondary location. For example, a dental hygienist nicking the gum with a sharp tool can lead to a local infection in the gum by Streptococcus bacteria of the normal oral microbiota. These Streptococcus spp. When an infection becomes disseminated throughout the body, we call it a systemic infection.
For example, infection by the varicella-zoster virus typically gains entry through a mucous membrane of the upper respiratory system. It then spreads throughout the body, resulting in the classic red skin lesions associated with chickenpox. Since these lesions are not sites of initial infection, they are signs of a systemic infection. Sometimes a primary infection , the initial infection caused by one pathogen, can lead to a secondary infection by another pathogen.
For example, the immune system of a patient with a primary infection by HIV becomes compromised, making the patient more susceptible to secondary diseases like oral thrush and others caused by opportunistic pathogens.
Similarly, a primary infection by Influenzavirus damages and decreases the defense mechanisms of the lungs, making patients more susceptible to a secondary pneumonia by a bacterial pathogen like Haemophilus influenzae or Streptococcus pneumoniae.
Some secondary infections can even develop as a result of treatment for a primary infection. Antibiotic therapy targeting the primary pathogen can cause collateral damage to the normal microbiota, creating an opening for opportunistic pathogens.
Anita, a year-old mother of three, goes to an urgent care center complaining of pelvic pressure, frequent and painful urination, abdominal cramps, and occasional blood-tinged urine. Suspecting a urinary tract infection UTI , the physician requests a urine sample and sends it to the lab for a urinalysis. Since it will take approximately 24 hours to get the results of the culturing, the physician immediately starts Anita on the antibiotic ciprofloxacin.
The next day, the microbiology lab confirms the presence of E. After taking her antibiotics for 1 week, Anita returns to the clinic complaining that the prescription is not working. Although the painful urination has subsided, she is now experiencing vaginal itching, burning, and discharge. After a brief examination, the physician explains to Anita that the antibiotics were likely successful in killing the E.
The new symptoms that Anita has reported are consistent with a secondary yeast infection by Candida albicans , an opportunistic fungus that normally resides in the vagina but is inhibited by the bacteria that normally reside in the same environment. To confirm this diagnosis, a microscope slide of a direct vaginal smear is prepared from the discharge to check for the presence of yeast. A sample of the discharge accompanies this slide to the microbiology lab to determine if there has been an increase in the population of yeast causing vaginitis.
After the microbiology lab confirms the diagnosis, the physician prescribes an antifungal drug for Anita to use to eliminate her secondary yeast infection. For a pathogen to persist, it must put itself in a position to be transmitted to a new host, leaving the infected host through a portal of exit Figure 6. As with portals of entry, many pathogens are adapted to use a particular portal of exit.
Similar to portals of entry, the most common portals of exit include the skin and the respiratory, urogenital, and gastrointestinal tracts. Coughing and sneezing can expel pathogens from the respiratory tract. A single sneeze can send thousands of virus particles into the air.
Secretions and excretions can transport pathogens out of other portals of exit. Feces, urine, semen, vaginal secretions, tears, sweat, and shed skin cells can all serve as vehicles for a pathogen to leave the body. Pathogens that rely on insect vectors for transmission exit the body in the blood extracted by a biting insect.
Similarly, some pathogens exit the body in blood extracted by needles. Figure 6. Pathogens leave the body of an infected host through various portals of exit to infect new hosts. Which pathogen is most virulent? Skip to main content. Microbial Mechanisms of Pathogenicity. Search for:. The suspected pathogen can be isolated and grown in pure culture.
A healthy test subject infected with the suspected pathogen must develop the same signs and symptoms of disease as seen in postulate 1. The pathogen must be re-isolated from the new host and must be identical to the pathogen from postulate 2. Which is more closely related to the severity of a disease? Think about It Explain the difference between a primary pathogen and an opportunistic pathogen. Describe some conditions under which an opportunistic infection can occur.
What portal of entry did the bacteria use to cause this infection? A Secondary Yeast Infection Anita, a year-old mother of three, goes to an urgent care center complaining of pelvic pressure, frequent and painful urination, abdominal cramps, and occasional blood-tinged urine.
Why was Candida not killed by the antibiotics prescribed for the UTI? Think about It List three conditions that could lead to a secondary infection.
Virulence , the degree to which a pathogen can cause disease, can be quantified by calculating either the ID 50 or LD 50 of a pathogen on a given population. Primary pathogens are capable of causing pathological changes associated with disease in a healthy individual, whereas opportunistic pathogens can only cause disease when the individual is compromised by a break in protective barriers or immunosuppression. Infections can be classified as local , focal , or systemic depending on the extent to which the pathogen spreads in the body.
Pathogens enter the body through portals of entry and leave through portals of exit. The stages of pathogenesis include exposure , adhesion , invasion , infection , and transmission. Staphylococcus aureus Pseudomonas aeruginosa Human immunodeficiency virus Salmonella enterica serovar Typhimurium Show Answer Answer c.
Show Answer Answer a. Pathogen A is most virulent. Show Answer Answer c. The correct order is exposure, adhesion, invasion, then infection. Show Answer An opportunistic pathogen causes disease only when conditions are favorable for the microorganism because of transfer to an inappropriate body site or weakened immunity in an individual.
Show Answer A focal infection is a small region of infection from which a pathogen may move to another part of the body to establish a second infection. Show Answer Cilia, fimbriae, and pili are all examples of structures used by microbes for adhesion.
Think about It Diseases that involve biofilm-producing bacteria are of serious concern. They are not as easily treated compared with those involving free-floating or planktonic bacteria. Explain three reasons why biofilm formers are more pathogenic. A microbiologist has identified a new gram-negative pathogen that causes liver disease in rats. Acupuncture is a form of alternative medicine that is used for pain relief. Explain how acupuncture could facilitate exposure to pathogens.
Scientists in CDER conduct many programs to advance regulatory science and research on pathogens -- agents that cause infection or disease. CDER is charged with advancing public health through the review, regulation, and research of potential treatments.
How does the study of bacteria and viruses help drug development and review? Pathogens include viruses, bacteria, fungi, and parasites that invade the body and can cause health issues. Anthrax, HIV, Epstein-Barr virus, and the Zika virus, among many others are examples of pathogens that cause serious diseases. A key component of our mission is to ensure that decisions involving drug approvals are based on the best available science. In order to do this, we benefit from having expert knowledge and first-hand experience with emerging diseases and the latest technologies for diagnosis and treatment.
CDER regulates many products used to treat patients with infectious diseases caused by pathogens, so it is important that we understand how infections become diseases and how pathogens interact within the human body. The research helps us understand some of the issues that may be encountered when potential drug products are developed for specific infectious diseases. We have to make sure that we ask the right questions when reviewing potential treatments.
The better we understand pathogens and the products used to treat the infectious diseases they cause, the better we will be at regulating the products to treat them. We can use our knowledge to understand what questions need to be asked to address potential safety issues.
For example, we can use animal models to understand the changes that correlate with protection and use those as biomarkers. In short, the knowledge we gain from our research often translates into more targeted reviews and faster approvals of treatments for infections. This enabled us to investigate interactions between the host and the pathogen, and to study the effectiveness of potential treatments.
Another success occurred during the Ebola outbreak last year. The laboratory directed by Dr. Kathleen Clouse Director, DBRR I developed better investigative procedures to study the Ebola virus by using non-infectious components of the virus to study how it enters and infects human cells. We are now able to test potential treatments that block Ebola entry or replication without exposure to use infectious virus.
Her lab is developing a similar system for the Zika virus. My lab developed a new model of infection with Zika virus in immunologically competent mice. It is a mouse model that will allow us to study the immune response to the virus.
By understanding what immune cells are important in the response to Zika infection and which contribute to the disease, we can perform better risk assessments for proposed therapeutics. After the replication cycle is complete, these new viruses are released from the host cell. This usually damages or destroys the infected cells. Some viruses can remain dormant for a time before multiplying again. When this happens, a person appears to have recovered from the viral infection , but gets sick again.
Antibiotics do not kill viruses and therefore are ineffective as a treatment for viral infections. Antiviral medications can sometimes be used, depending on the virus. Bacteria are microorganisms made of a single cell. They are very diverse, have a variety of shapes and features, and have the ability to live in just about any environment, including in and on your body. Not all bacteria cause infections. Those that can are called pathogenic bacteria. Your body can be more prone to bacterial infections when your immune system is compromised by a virus.
The disease state caused by a virus enables normally harmless bacteria to become pathogenic. Antibiotics are used to treat bacterial infections. Some strains of bacteria have become resistant to antibiotics, making them difficult to treat. This can happen naturally, but also happens because of the overuse of antibiotics, according to the World Health Organization WHO. There are millions of different fungal species on Earth. Just or so are known to cause sickness.
Fungi can be found just about everywhere in the environment, including indoors, outdoors, and on human skin. They cause infection when they overgrow. Fungi cells contain a nucleus and other components protected by a membrane and a thick cell wall. Their structure can make them harder to kill. Some new strains of fungal infections are proving to be especially dangerous , such as Candida aurus , and have prompted more research into fungal infections.
Parasites are organisms that behave like tiny animals, living in or on a host and feeding from or at the expense of the host.
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