PARASITIC AND FUNGAL INFECTIONS Flashcards
When a parasite enters a host, there are several possible results.
1. First, there may be no infection at all, because the host’s [?] prevents the parasite from establishing an infection.
2. The parasite may invade the host, become established, and then be killed and eliminated by [?]
3. The parasite may overwhelm and [?] the host
4. Long-lasting infection in which the host begins to [?] the parasite but cannot remove it completely
5. Host mounts a response that [?] not only the parasite but also host tissues.
innate immunity
host defense mechanisms
kill
eliminate
attacks
If a parasite becomes sequestered within host cells, the parasite is protected. Example:
tissue protozoans
Some parasites disguise themselves by acquiring host antigens. Example:
Schistosomes
Antigenic variation. Example:
African trypanosomes
Antigen shed from the parasite. Example:
Entamoeba histolytica
Molecular mimicry. Example:
Chaga’s disease
is responsible for the production of cytokines and chemokines, which enhance the cytotoxic function of effector cells, increase the numbers of immune cells, and attract immune cells to the site of infection
Cellular immunity
The immunoglobulin response to parasites includes formation of [?].
IgM, IgG, IgA, and IgE antibodies
[?] can damage protozoa, neutralize parasites by blocking attachment to the host cell, prevent the spread of the parasite, promote complement lysis, and enhance phagocytosis and destruction through antibody-dependent cellular cytotoxity.
Specific antibody
Eosinophil-specific granules contain several different proteins:
major basic protein, eosinophil cationic protein, eosinophil peroxidase, and eosinophil-derived neurotoxin
These cells are capable of phagocytosis but are much less efficient than neutrophils because of the smaller numbers of
major basic protein, eosinophil cationic protein, eosinophil peroxidase, and eosinophil-derived neurotoxin.
Their most important role is neutralizing basophil and mast cell products and killing certain parasites
major basic protein, eosinophil cationic protein, eosinophil peroxidase, and eosinophil-derived neurotoxin.
[?], a bloodborne parasite, is transmitted exclusively through
Malaria
Malaria Specie:
Anopheles minimus flavirostris (female mosquitos)
Transmission is more intense in areas in which the mosquito lifespan is longer, and where it prefers to bite [?] rather than other animals. This allows the parasite to have time to complete its development inside the mosquito.
humans
Four types of human malaria
Plasmodium falciparum
Plasmodium vivax
Plasmodium malariae
Plasmodium ovale
- Most common
Plasmodium falciparum
Plasmodium vivax
- Most deadly
Plasmodium falciparum
Monkey malaria
Plasmodium knowlesi
remains the “gold standard” for laboratory confirmation of malaria.
Microscopic examination
Malaria antibody detection is performed using the
indirect fluorescent antibody (IFA) test.
The can be used to determine if a patient has been infected with Plasmodium.
IFA
Because of the time required for development of antibody and also the persistence of antibodies, [?] is not practical for routine diagnosis of acute malaria.
serologic testing
Rapid Test Kits
Pan Lactate Dehydrogenase
Histidine Rich Protein 2
Aldolase
: for all Plasmodium specie
Pan Lactate Dehydrogenase
: specific for Plasmodium falciparum
Histidine Rich Protein 2
: specific for Plasmodium falciparum and Plasmodium vivax
Aldolase
Incorporated w/ enzymes
Rapid Test Kits
are common and harmless inhabitants of skin and mucous membranes under normal conditions (e.g., Candida albicans).
Fungi
In immunocompromised hosts, [?] become opportunistic agents that take advantage of the host’s weakened resistance.
Candida spp. and other fungi
Manifestations of fungal disease may range from unnoticed respiratory episodes to rapid, fatal dissemination of a violent [?].
hypersensitivity reaction
Survival mechanisms of fungi that successfully invade the body are similar to bacterial characteristics and include the following:
- presence of an antiphagocytic capsule
- resistance to digestion within macrophages
- destruction of phagocytes (e.g., neutrophils).
CANDIDIASIS Causative agent
Candida albicans
• It is the most common cause of all serious fungal diseases
Candida albicans
CANDIDIASIS Diagnosis
- Immunodiffusion and Counterimmunoelectrophoresis tests
- Latex Agglutination
- Enzyme Immunoassay
- Reverse passive agglutination test
A titer of 1:4 suggests an
early infection, colonization, or a nonspecific reaction.
A titer of 1:8 or greater,
conversion from a negative to a positive test
a fourfold increase in titer is presumptive evidence of
invasive infection.
A fourfold decrease in titer may indicate
successful therapy
COCCIDIOMYCOSIS Causative agent
Coccidiodes immitis
COCCIDIOMYCOSIS Diagnosis
- Complement fixation test
- Tube precipitation Test
- Immunodiffusion
- Latex agglutination
- EIA
- most widely used quantitative serodiagnostic method
Complement fixation test
- presumptive evidence of an early infection and should be repeated in 3 to 4 weeks.
1:2 to 1:4
- indicative of an active infection
1:16
- highly specific with very few cross-reactions
Tube precipitation Test
more preferred; confirmatory test
Tube precipitation Test
- highly specific when reference antisera are used
Immunodiffusion
Long-lasting infection in which the host begins to eliminate the parasite but cannot remove it completely
Ex. Infection to [?] (nematode: roundworm)
Ascaris lumbricoides
invade macrophages and liver cells, and temporarily hidden from the immune system
tissue protozoans
most romantic parasite
Schistosomes
blood flukes
Schistosomes
survives in an unprotected blood vessel
Schistosomes
the invading form (Schistosomula) acquires RBC Ags that determines the blood group
Schistosomes
evade the immune response by periodically changing their
surface Ags
African trypanosomes
a variant surface glycoprotein will produce unlimited
group of variable Ag type
African trypanosomes
Most common cause of amoebiasis
Entamoeba histolytica
shed Ab attaches to Ag, but not to the parasite
Entamoeba histolytica
Chaga’s disease causative agent:
Trypanosoma cruzi
may result from parasitic Ag similar to those that are
normally present in the host tissue
Chaga’s disease
may result from parasitic Ag similar to those that are
normally present in the host tissue
Chaga’s disease
may lead to autoimmune problems (cardiac and intestinal
consequences)
Chaga’s disease
– most effective cell in killing parasites
Eosinophil
– most effective immunoglobulin; it attaches to eosinophils to aid in the release of granules for killing parasites
IgE
– attaches the part of the Ab to the surface of eosinophils
Fc portion
TOXOPLASMOSIS Etiologic agent
Toxoplasma gondii
a ubiquitous protozoan parasite that infects.humans by ingestion of infective cysts (oocysts)
Toxoplasma gondii
Toxoplasma gondii Transmission
- hand-to-mouth contact from contaminated soil or cat litter
- Ingesting gocysts in raw or partially cooked pork, mutton, or beef
- blood transfusions or organ transplantation
trigger phagocytosis, which ultimately destroys the organism.
• Antibody-coated Toxoplasma organisms
- fourfold increase in the titer of IgG, or high levels of IgM and IgG antibodies are considered diagnostic
- Enzyme immunoassays (EIA) for IgM, IgG, or IgA
- Indirect Fluorescent Antibody (IFA) assays for IgG - congenital toxoplasmosis
- PCR - method of choice to detect T. gondii DNA in CSF
Hematologic test
Microscopy
o Dipped in distilled water: to dehemoglobinize
Thick Smear
o Used for malaria survey (presence or absence of malaria)
Thick Smear
o stained w/ Giemsa (Romanowsky stain)
Thin Smear
o Used for Plasmodium specie identification
Thin Smear
