Target Health Blog


April 19, 2021


Washing one's hands, is an effective way to prevent the spread of infectious disease.

Photo credit: by Lars Klintwall Malmqvist (Larsklintwallmalmqvist) - Own work, Public Domain; Wikipedia Commons

Primary pathogens cause disease as a result of their presence or activity within the normal, healthy host, and their intrinsic virulence is, in part, a necessary consequence of their need to reproduce and spread. Many of the most common primary pathogens of humans only infect humans. However, many serious diseases are caused by organisms acquired from the environment or that infect non-human hosts.

An 1) _____ is the invasion of an organism's body tissues by disease-causing agents. Infections can be caused by a wide range of pathogens, most prominently bacteria and viruses but also more unusual types. Hosts can fight infections using their immune system. Mammalian hosts react to infections with an innate response, involving inflammation, followed by an adaptive response.

Specific medications used to treat infections include antibiotics, antivirals, antifungals, antiprotozoals, and antihelminthics AKA (2) _____). Infections are caused by infectious agents including:

1.     Bacteria (Mycobacterium tuberculosis, Staphylococcus aureus, Escherichia coli, Clostridium botulinum, and Salmonella spp.)

2.     Viruses and related agents such as viroids (HIV, Rhinovirus, Lyssaviruses such as Rabies virus, Ebolavirus and SARS-CoV-2)

3.     Fungi, further subclassified into: Ascomycota, including 3) _____ such as Candida, filamentous fungi such as Aspergillus, Pneumocystis species, and dermatophytes.

4.     Basidiomycota, including the human-pathogenic genus Cryptococcus.

5.     Prions

6.     Parasites, which are usually divided into:

a.     Unicellular organisms (e.g. malaria, Toxoplasma, Babesia)

b.     Macroparasites (worms or helminths) including nematodes such as parasitic roundworms and pinworms, tapeworms (cestodes), and flukes (trematodes, such as schistosomiasis)

c.     Arthropods such as 4) _____, mites, fleas, and lice.

Symptomatic infections are apparent and clinical, whereas an infection that is active but does not produce noticeable 5) _____ may be called inapparent, silent, subclinical, or occult. An infection that is inactive or dormant is called a latent infection. An example of a latent bacterial infection is latent tuberculosis. Some viral infections can also be latent, examples of latent viral infections are any of those from the Herpesviridae family.

Different terms are used to describe infections. The first is an acute infection in which symptoms develop rapidly and its course can either be rapid or protracted. The next is a chronic infection. A chronic infection is when symptoms develop gradually, over weeks or months, and are slow to resolve. A subacute infection is one in which symptoms take longer to develop than in an acute infection but arise more quickly than a chronic infection. A latent infection is a type of infection that may occur after an acute episode when the organism is present but symptoms are not and after time, the disease can reappear. A focal infection is defined as the initial site of infection from which organisms travel via the 6) _____ to another area of the body.

Opportunistic pathogens can cause an infectious disease in a host with depressed resistance (7) _____) or if they have unusual access to the inside of the body (for example, via trauma). Opportunistic infections may be caused by microbes ordinarily in contact with the host, such as pathogenic bacteria or fungi in the gastrointestinal or the upper respiratory tract, and they may also result from (otherwise innocuous) microbes acquired from other hosts (as in Clostridium difficile colitis) or from the environment as a result of traumatic introduction (as in surgical wound infections or compound fractures). An opportunistic disease requires impairment of host defenses, which may also occur as a result of genetic defects (such as Chronic granulomatous disease), exposure to antimicrobial drugs or immunosuppressive agents (as might occur following poisoning or cancer chemotherapy), exposure to ionizing radiation, or as a result of an infectious disease with immunosuppressive activity (such as with measles, malaria or HIV disease).

A 8) _____ infection is a sequela or complication of that root cause. For example, an infection due to a burn or penetrating trauma as the root cause. Primary pathogens often cause primary infection and often cause secondary infection. Usually, opportunistic infections are viewed as secondary infections since immunodeficiency or injury was the predisposing factor.

Other types of infection consist of mixed, iatrogenic, nosocomial, and community-acquired infection. A mixed infection is an infection that is caused by two or more pathogens. An example of this is Appendicitis, which is caused by Bacteroides fragilis and Escherichia coli. The second is an iatrogenic infection. This type of infection is one that is transmitted from a health care worker to a patient. Nosocomial infections are those that are acquired during a hospital stay. Lastly, a community-acquired infection is one in which the infection is acquired from a whole community.

Infections can be classified by the anatomic location or organ system infected, including:

?        9) _____ tract infection

?        Skin infection

?        Respiratory tract infection

?        Odontogenic infection (an infection that originates within a tooth or in the closely surrounding tissues)

?        Reproductive organ infections

?        Intra-amniotic infection

Diagnosis of infectious disease is nearly always initiated by medical history and physical examination. More detailed identification techniques involve the culture of infectious agents isolated from a patient. 10) _____ allows identification of infectious organisms by examining their microscopic features, by detecting the presence of substances produced by pathogens, and by directly identifying an organism by its genotype. Other techniques (such as X-rays, CAT scans, PET scans or NMR) are used to produce images of internal abnormalities resulting from the growth of an infectious agent. The images are useful in detection of, for example, a bone abscess or a spongiform encephalopathy produced by a prion.

ANSWERS: 1) infection; 2) worms; 3) yeasts; 4) ticks; 5) symptoms; 6) bloodstream; 7) immunodeficiency; 8) secondary; 9) Urinary; 10) Culture

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