MODULE 1 Unit 4: Laboratory Diagnosis of Parasitic Infections Flashcards
There are two (2) approaches in the diagnosis of parasitic infections: clinical and laboratory.
- Clinical Diagnosis
- Laboratory Diagnosis
The clinical manifestations of parasitic diseases are so (?) that in most instances diagnosis based on symptomatology alone is inadequate. .
non-specific
Although, an experienced physician may recognized characteristic signs and symptoms of certain parasitic diseases, the symptoms in (?) may be so confusing that no clear clinical picture is presented. This provides provisional diagnosis only
atypical cases
Physician also suspects that the person has an infection rather than another type of illness based on patient
clinical history.
It is designed to discover epidemiologic risk factors such as, but not limited to
past medical history, place of residence, travel, occupation, outdoor activities, family, food, and drinking water
Specific examples of the importance of each of these follow.
• (?) should be suspected in a patient with unexplained fever and with the history of travel to rural area in Palawan.
• A history of hiking and drinking stream water is classically associated with (?).
• A gastrointestinal disease characterized by abdominal pain and diarrhea that follows after eating uncooked freshwater or brackish water fish may be associated with (?)
Malaria
giardiasis
Capillaria philippinensis infection
A parasitology laboratory uses appropriate test method to be able to:
• Confirm or rule out a (?) that the disease is parasitic in nature.
• Identify (?( infection
clinical suspicion
unsuspected
To confirm means to state that the disease is due to (?), and what species of parasite is present.
To rule out means to (?) as the cause of the disease.
parasitic infection
exclude or to eliminate parasite
Unrecognizedorsubclinicalinfectionsposeathreatbecause manyparasitescanbetransmittedwhensymptomsare either
mildortotallyabsent.
Accurate diagnosis of a parasitic disease provide (?) thus preventing possible complications that may arise. It can also provide accurate (?) that are important in the surveillance and monitoring of diseases.
prompt treatment
prevalence and incidence
Laboratory diagnosis of parasitic infections is done either by
direct or indirect methods
involves the demonstration of the parasite (e.g., adults, eggs, larvae, cysts, or trophozoites), or parasite components (e.g., antigens and DNA) in the specimen. This provides definitive diagnosis of parasitic infection.
Direct method
tests for the evidence of parasitic infection other than actually finding the organism itself. This provides only presumptive evidence of infection.
Indirect method
Parasitic infections are usually diagnosed by examination of a specimen/ material under the microscope.
Microscopic method
Microscopic method is basically a two-step process:
(1) detection of the (?), and
(2) identification based on
parasite
distinctive morphologic characteristics
Among others factors, this requires the availability of (?) and a well-trained and experienced (?).
good microscope
microscopist
The need for highly invasive procedures to collect samples g. tissue, which may induce medical complications, undermines the utility of this method.
Microscopic method
The most common procedure performed in the area of parasitology is the examination of a stool specimen for
ova and parasites (O&P exam)
refers to the egg stage of select parasites and parasites encompass the other morphologic forms that may be present
ova
Appropriate specimen is examined microscopically by (?) for parasite diagnostic stage
direct wet mounts, wet mounts of concentrates, or permanent stains
- Cysts/trophozoites of (?)
-Oocysts of (?)
-Eggs of (?) - Rhabditiform larvae of
Entamoeba histolytica, Giardia lamblia, Balantidium coli
Cystoisospora belli, Cryptosporidium parvum, Cyclospora cayetanensis, Sarcocystis spp.
Ascaris lumbricoides, Trichuris trichiura, hookworm spp. Capillaria philippinensis, Diphyllobothrium latum, Taenia spp., Hymenolepis nana, Hymenolepis diminuta, Dipylidium caninum, Fasciola spp, Clonorchis sinensis, Opisthorchis spp, Fasciolopsis buski, Echinostoma ilocanum, heterophyids, Schistosoma japonicum, Schistosoma mansoni
Strongyloides stercoralis
Being generally a (?), this remains as the gold standard in most laboratories especially in the diagnosis of common protozoan and helminth infections. However, it is characterized by low sensitivity when parasites are low in numbers such as in light infections ,or during pre-patent and chronic periods of infection, hence, direct microscopic examination may yield false negative results. Concentration technique circumvents this problem
simple and low cost technique
Giardia lamblia trophozoites, Cryptosporidium spp., Cystoisospora belli, Strongyloides stercoralis and eggs of Fasciola hepatica or Clonorchis sinensis
Duodenal material
Entamoeba histolytica
Sigmoidoscopy specimen
Enterobius vermicularis
Perianal swab
Plasmodium spp., Babesia spp., Leishmania spp., Trypanosoma spp. Wuchereria bancrofti, Brugia malayi, Loa loa, Mansonella spp.
Blood
Trichomonas vaginalis, Wuchereria bancrofti, Schistosoma haematobium.
Urine
- Paragonimus westermani
- Occasionally, larvae of Strongyloides stercoralis, Ascaris lumbricoides, and hookworm spp.
Sputum
Trypanosoma brucei, Naegleria, Acanthamoeba
Cerebrospinal fluid
Trichomonas vaginalis
Genital tract specimen
Muscle biopsy specimen: Trichinella spiralis
Tissue and aspirates
Histopathological examination of brain: Naegleria and Acanthamoeba
Tissue and aspirates
Spleen and bone marrow aspirate: Leishmania donovani
Tissue and aspirates
Duodenal aspirates: Trophozoites of Giardia lamblia
Tissue and aspirates
Liver pus: Trophozoites of Entamoeba histolytica in cases of amebic liver abscess
Tissue and aspirates
Culture methods using xenic or axenic media have been described for some protozoan parasites:
Trichomonas vaginalis, Leishmania spp., Trypanosoma cruzi, Entamoeba histolytica, Acanthamoeba spp., or Naegleria fowleri.
is examined microscopically. This approach may be helpful when routine procedures have failed to provide a diagnosis.
Material from culture
But few clinical laboratories undertake the task because of :
infrequent requests, lack of familiarity with methods, the need for special equipment, supplies, and reagents, and the waiting period for several days or weeks for the result.
Culture protozoa grown in association with an unknown microbiota are called a (?).
xenic culture
If they are grown in association with a single known bacterium, the culture is (?)
monoxenic
if the culture contains several identified bacteria, then it is (?).
polyxenic
If protozoa are grown as pure culture without any bacterial associate, the culture is (?).
axenic
(?) is used for maintaining QC strains and for research purposes.
Axenic culture
(?) may be used as a supplemental diagnostic procedure.
Xenic cultures
This is a method for diagnosing a disease in humans by inoculating the specimen suspected of harboring causative parasite into a laboratory-bred, parasite-free animal of a different species. where the parasite is allowed to multiply. The laboratory animal is later microscopically examined for the presence of the parasite.
Xenodiagnosis
In the diagnosis of (?), an uninfected reduviid bug is allowed to feed on patient’s blood and the bug’s feces is then examined to observe for the presence of Trypanosoma cruzi.
Chagas’ disease
In the diagnosis of Chagas’ disease, an uninfected reduviid bug is allowed to feed on patient’s blood and the bug’s feces is then examined to observe for the presence of (?).
Trypanosoma cruzi
Muscle tissue form a patient suspected of having (?) is fed to uninfected rat.
trichinosis
The rat is then checked, after the appropriate time, for the presence of (?), particularly in the diaphragm.
Trichinella spiralis larvae
This enables a diagnosis if very low numbers of parasites occur in the specimen. However, because a period of incubation between infection of the laboratory animal and examination is necessary, there is a long period of time until the final result. This procedure is rarely requested and not available in most clinical laboratories
Xenodiagnosis
[Greek xenos, stranger, alien; + diagnosis)
Xenodiagnosis
Specimen may also be examined grossly for parasite stage that are large enough to be seen by the naked eye, such as some adult worms, and proglottids of tapeworms.
Macroscopic examination
for diagnosis of parasitic infections
Immunodiagnostic methods
Immunodiagnostic methods for diagnosis of parasitic infections are basically of two types: (a) [?], and (2) [?].
(a) antigen detection, and (2) antibody detection.
They permit batch processing, and do not require experienced microscopists.
Immunodiagnostic method
Immunoassays that test specimens for the presence parasite antigens use known commercially prepared specific antibodies.
Antigen detection
There are limited number of pathogenic parasites that can be diagnosed by antigen detection test.
Antigen detection
Stool: Giardia lamblia, Cryptosporidiumspp., Entamoeba histolytica/Entamoeba dispargroup
Antigen detection
Blood or serum : Plasmodium spp., Wuchereria bancrofti
Antigen detection
Vaginal swabs: Trichomonas vaginalis
Antigen detection
Test formats for antigen detection methods include:
direct fluorescent antibody (DFA), enzyme immunoassay (EIA), and lateral flow (immunochromatography) assays (LFAs).
methods are more reliable and a positive test result is indicative of current infections.
Antigen detection
In general, they have good or superior sensitivities and specificities, are easy to use and have quicker turnaround times when compared to routine microscopic examination.
Antigen detection
is performed to determine the presence of antibodies
blood (serum) test
which is an immune response formed against parasitic antigens, to provide evidence of infection.
antibody
They are recommended in the diagnosis of infections caused by parasites that reside in the host deep tissues and invasive techniques are necessary to obtain specimen which can pose some risk to the patient, or in occult infections where parasites cannot be isolated in the specimen.
Antibody detection (serology test)
An (?)for parasitic infection may provide early detection when significant levels of antibodies are produced before the patent stage.
antibody test
However, in some people, parasitic infections may not stimulate (?) or seroconversion may be delayed with onset of clinical symptoms.
antibody response
The detection of against against a given parasite in a patient with no previous exposure and no recent history of travel to an endemic area can be considered a (?).
positive result
A (?) may be produced when examining individuals from endemic areas.
false positive test
It does not distinguish between active and previous infection because (?) may decline slowly and persist even after cure. Therefore, the results of antibody tests in the diagnosis of parasitic infections must be interpreted cautiously.
antibodies
Historically, (?) for parasitic diseases have been plagued by low sensitivity and specificity, primarily owing to the complex antigenic nature of parasites and the possibilities for crossreactions from related species.
serologic procedures
The introduction of newer test methods combined with the use of more (?)s is providing more accurate results.
highly defined antigenic component
Many of the newer tests use the (?), although IFA, indirect hemagglutination (IHA), complement fixation (CF), and bentonite flocculation (BF) methods remain popular.
EIA or immunoblot (Western blot) format
(?) for parasite identification offers high levelsof sensitivity and specificity, ability to differentiate morphologically similar organisms, lack of reliance on subjective microscopic features, and may also be used to monitor the success of antiparasitic therapy.
Nucleic acid amplification tests (NAATs)
However, several challenges exist for widespread implementation of(?), including the expense of reagents and equipment, need for sophisticated facilities and are prone to cross-contamination if proper processing precautions are not strictly enforced.
molecular diagnostics
Different types of NAATs include:
polymerase chain reaction (PCR) and real-time reverse transcription (RT) PCR
random amplified polymorphic DNA (RAPD)
amplified fragment length polymorphism (AFLP)
restriction fragment length polymorphism (RFLP)
microsatellite marker method
Luminex xMAP-based technology (areas of multianalyte profiling)
loop-mediated isothermal amplification (LAMP)
Other testing modalities
a. Skin test
b. Radiologic examination
c. Hematology
are performed by injecting parasitic antigen intradermally and observing the reaction.
Skin tests
In immediate hypersensitivity reaction, (?) is seen within 30 minutes of infection
wheal and flare response
(?) seen after 48 hours of injection is called as delayed hypersensitivity reaction.
erythema and induration
• Montenegro test:
Kala-azar (Leishmania donovani)
• Bachman intradermal test:
Trichinellosis (Trichinella spiralis)
• Casoni’s test:
Hydatid disease (Echinococcus granulosus)
These tests are used to look for some parasitic diseases that may cause lesions in the organs.
X-ray, Ultrasonography (USG)
Magnetic Resonance Imaging (MRI) scan
Computed Tomography (CT) scan.
is frequently seen in hookworm infection and malaria.
Anemia
is frequently present in helminthic infections.
Eosinophilia
occurs in visceral leishmaniasis.
Hypergammaglobulinemia
is seen in amoebic liver abscess.
Leukocytosis
is the sum of all the activities necessary to produce consistently accurate and precise results.
Quality assurance (QA)
In a diagnostic parasitology laboratory, it is a guarantee that the information in the laboratory result can be relied upon by the physician to confirm or rule out parasitic infections.
QA
refers to a system in which there is continuous improvement in reliability, efficiency, and utilization of laboratory services
Quality assurance
It encompasses the entirety of the process beginning when a physician orders a laboratory test and ending with the physician interpreting the results
Quality assurance (QA)
includes activities performed before the actual laboratory manipulation that influence the quality of laboratory results.
pre-analytical phase
- Pre-analytical phase:
a. Test ordering and request forms
b. Proper specimen collection, storage, and transport
c. Specimen receipt and accessioning
d. Training of personnel
The requesting physician must have an understanding of which laboratory tests are appropriate to order in the diagnosis, monitoring, or even screening for parasitic infection.
Test ordering and request forms
Proper request forms must be used and contain information to correctly identify the
source/type of the sample, patient’s name and identification number, the physician’s name, and the date and time of sample collection.
Where applicable, patients are given written and/or verbal instructions to facilitate collection of specimen for adequate detection.
Proper specimen collection, storage, and transport
• Correct type of specimen and/or (?) of specimen collection
• Appropriate (?)
• (?). Certain medications and substances may interfere with the detection of parasites, thus should be avoided starting days before and continuing through the test period.
• Acceptable amount or (?) of the specimen
• Manner of specimen collection, storage, transport
• Proper specimen (?) (source/type of specimen the patient’s name and identification number, the physician’s name, and the date and time of sample collection)
• Use of (?)
• (?) from sample collection to receipt and examination in the laboratory.
time
specimen container
Patient preparation
volume
labelling
preservatives
Time frame
• Correct type of specimen and/or (?) of specimen collection
• Appropriate (?)
• (?). Certain medications and substances may interfere with the detection of parasites, thus should be avoided starting days before and continuing through the test period.
• Acceptable amount or (?) of the specimen
• Manner of specimen collection, storage, transport
• Proper specimen (?) (source/type of specimen the patient’s name and identification number, the physician’s name, and the date and time of sample collection)
• Use of (?)
• Time frame from sample collection to receipt and examination in the laboratory.
time
specimen container
Patient preparation
volume
labelling
preservatives
Ensurethat allspecimensareaccompanied with a complete laboratory request form and theinformation on the request form should correspond with the details of the patientand those on the specimen container.
Specimen receipt and accessioning
Ensure that all specimens arrive in the laboratory assoon as after collection within time limit recommendation.
Specimen receipt and accessioning
is maintained to track the specimen received into the laboratory.
record system
The person advising the patient or medical staff must be adequately trained in all facets of specimen collection.
Training of personnel
The person performing the parasitologic examination must be familiar with appropriate technical procedures to be used for each type of specimen and morphologic recognition and differentiation of parasites.
Training of personnel
DIRECT methods of diagnosis for parasitic infections
Routine stool O & P exam
Perianal scotch tape swab (enterobiasis)
RT-PCR
OptiMal test for malaria
Xenodiagnosis
INDIRECT methods of diagnosis for parasitic infections
Montenegro skin test
WBC differential count
MRI
X-ray
Rapid antibody test
variables affecting Proficiency Test (PT) result
- Sample handling and transport
- Equipment management
- Preparation of reagents
- Carryover from previous sample
- Personnel competency on detection and identification of parasites
- Turnaround times
- Transcription of results
- Clinical management
Exemption to variables affecting Proficiency Test (PT) result
Instruction for patient preparation
Sample collection
