Question 1

A parasite accesses a target cell in a host,thus hiding its antigens from the host's immune system.This survival strategy is known as:

Accepted Answer

Antigenic concealment refers to the strategy used by some parasites to hide their antigens within host cells, thereby avoiding detection by the host's immune system. This allows the parasite to survive and replicate without being targeted and destroyed by the immune response.

Question 2

Suppose a parasite invades a patient and causes disease.The patient develops an immune response and has some resistance to the parasite but is not cured.This outcome is considered what type of host-parasite interaction?

Accepted Answer

Concomitant immunity is a type of host-parasite interaction where the host's immune response is able to control the parasite but not eliminate it completely. The parasite is unable to cause severe disease, but it also does not completely clear from the host's body. This differs from sterilizing immunity, which completely eliminates the parasite, and from symbiosis and commensalism, which describe interactions where the host and parasite have a mutually beneficial or neutral relationship.

Question 3

A 27-year-old female patient who is pregnant is undergoing serological testing as a precaution because of a recent food poisoning episode in which she ate undercooked pork at a picnic.The laboratory tests revealed positive IgG antibodies and negative IgM antibodies to toxoplasmosis.What do these test results indicate?

Accepted Answer

The presence of IgG antibodies and absence of IgM antibodies to toxoplasmosis indicate a past infection with the parasite, but not a recent or active infection. Therefore, there is no risk of transmission to the fetus. It is still important for the patient to practice good hygiene and avoid potential sources of infection.

Question 4

A patient has been diagnosed with tapeworm.Identify the type of parasitic organism involved.

Accepted Answer

Tapeworms are a type of helminth, which are parasitic worms that can live in the gastrointestinal tract of their host. Protozoa are single-celled organisms and ectoparasites are parasites that live on the outside of their host's body. Host refers to the organism that is being parasitized.

Question 5

A patient with candidiasis is considered to have which type of mycotic infection?

Accepted Answer

Candidiasis is considered an opportunistic infection because it often occurs in individuals with weakened immune systems, taking advantage of the compromised condition to cause disease.

Question 6

A complement fixation test for Histoplasma antibodies shows a 1:32 titer.This means the patient is negative for Histoplasma infection.

Accepted Answer

A titer of 1:32 indicates that the patient's blood sample reacted with the Histoplasma antigen in the test. This suggests the presence of Histoplasma antibodies in the patient's blood, which could be due to past or current infection. Therefore, the patient is not negative for Histoplasma infection.

Question 7

Which statement best describes antigenic variation of a parasite?

Accepted Answer

Antigenic variation refers to a parasite's ability to change their surface antigens or create new ones to evade the host's immune system.

Question 8

Serology assays are useful in the diagnosis of Aspergillus infections from bronchial lavage samples in immunocompromised patients.

Accepted Answer

Serology assays are generally not useful for diagnosing Aspergillus infections from bronchial lavage samples, as they are designed to detect antibodies in blood, not direct pathogens in bronchial samples. For diagnosing Aspergillus in such samples, culture or molecular methods are typically used.

Question 9

A patient presents with a fungal infection.Which components of the immune system are activated early in the course of the patient's infection?

Accepted Answer

Macrophages and dendritic cells are key players in the early response to fungal infections. They recognize and phagocytose fungal cells, and then present fungal antigens to T cells to initiate an adaptive immune response. Natural killer cells and antibodies play a role in immunity to viral infections, while polysaccharides and chitins are components of fungal cell walls that can stimulate an immune response but are not themselves immune system components. T cells and B cells are involved in the adaptive immune response to fungal infections but are not among the earliest responders.

Question 10

An example of a fungal organism that commonly causes systemic infections is:

Accepted Answer

Cryptococcus neoformans is a fungal organism that commonly causes systemic infections, particularly in individuals with weakened immune systems, such as those with HIV/AIDS or undergoing chemotherapy. It primarily affects the lungs and central nervous system, and can lead to severe illness or death if left untreated. Malassezia furfur and Trichophyton species are fungal organisms that primarily cause skin infections. Candida albicans can cause systemic infections in certain situations, but it is not as common as Cryptococcus neoformans.

Question 11

A parasite that causes the immune system to increase protein production to distract the immune system is using which survival strategy?

Accepted Answer

Immunologic diversion is a strategy where the parasite manipulates the host's immune response to focus on irrelevant targets, thereby distracting it from attacking the parasite itself.

Question 12

What approach can be used to decrease the chance of a false-positive result when performing latex agglutination to identify Cryptococcus infections?

Accepted Answer

Pretreating the specimen with heat and pronase can reduce the chance of a false-positive result by removing nonspecific inhibitors or agglutinators that may be present in the specimen. Mixing the specimen with India ink is used to visualize Cryptococcus under a microscope, but it does not affect the specificity of the latex agglutination test. Freezing the specimen may affect the viability of the organism, but it does not improve the specificity of the test. Waiting for the patient to be symptomatic before testing may delay proper diagnosis and treatment.

Question 13

A patient who has recently traveled to Africa presents to the physician with a possible parasitic infection.The physician orders serological testing.Which of the following conditions is best detected via serological testing?

Accepted Answer

Toxoplasmosis is best detected via serological testing because it involves measuring antibodies against the Toxoplasma gondii parasite.

Question 14

To correctly determine an infection with toxoplasmosis within the last 12 months,both IgG and IgM should be negative.

Accepted Answer

To correctly determine an infection with toxoplasmosis within the last 12 months, IgM should be positive and IgG can be either positive or negative. A negative result for both IgG and IgM would indicate a lack of current or past infection.

Question 15

A patient is diagnosed with coccidioidomycosis.This infection can be classified as:

Accepted Answer

Coccidioidomycosis is a systemic fungal infection caused by Coccidioides species. It typically affects the respiratory system but can spread to other organs, making it a systemic infection.

Question 16

Suppose a parasite invades a patient and causes disease.The patient develops immunity and is ultimately cured.This outcome is considered what type of host-parasite interaction?

Accepted Answer

Sterilizing immunity refers to immunity that completely eliminates the parasite from the host's body. In this scenario, the patient developed immunity and was ultimately cured, indicating that the immune response completely eliminated the parasite. This type of interaction is not symbiotic or commensalistic, as the parasite caused disease in the host. Concomitant immunity refers to immunity that develops in response to a second infection while the host is still infected with the first infection, which is not the case in this scenario.

Question 17

Eosinophilia and an increase in which immunoglobulin play a role in the defense against parasites?

Accepted Answer

Eosinophilia and an increase in IgE play a role in the defense against parasites. IgE binds to the surface of parasitic organisms and triggers the release of eosinophils, which then attack and eliminate the parasite.

Quiz 22: Serological and Molecular Diagnosis of Parasitic and Fungal Infections