Blood Serum Diagnostic Procedures For Intestinal Parasites

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Blood Serum Diagnostic Procedures For Intestinal Parasites

 

Center for Disease Control

 

 

Detection of Antibodies - General Information

 

Diagnosis of parasitic infections is definitively made by

identification of parasites in host tissue or excreta. Such

identification is not generally possible in diseases such as

toxoplasmosis or toxocariasis, in which parasites are located in deep

tissue sites, and is not initially recommended in diseases such as

cysticercosis or echinococcosis, in which invasive techniques with

some risk to the patient are necessary to obtain material. Detection

of antibodies can be very useful as an indicator that an individual

has been infected with a specific parasite. A positive result in a

person with no exposure to the parasite prior to recent travel in a

disease-endemic area may be interpreted as indicating recent

infection. However, detection of specific antibodies in a person

native to an area where the parasite is endemic may reflect only a

past infection unrelated to current clinical status. In general,

detection of antibodies to parasitic diseases indicates only infection

at some indeterminate time and not necessarily acute or current

infection. Levels of antibodies to parasites slowly decline after the

patient is cured of the infection but generally last for at least six

months to many years, depending on the infecting parasite, and thus

are not generally useful, real-time indicators of successful cure.

 

The detection of specific IgM and IgA antibodies may be of value in

determining the approximate time of initial infection with Toxoplasma

gondii, but is not recommended for any other parasitic disease. If

infection with a parasite is suspected and blood film, stool or urine

examinations are either not indicated or are negative, then the

appropriate serology test for specific IgG antibodies should be

requested. Tests for parasite-specific IgM, IgA, or IgE are generally

not useful for diagnosis and should not be requested. If the

parasite-specific IgG is negative, a positive IgM, IgA, or IgE result

is generally a false-positive reaction and should not be considered

when determining patient management.

 

The majority of antibody detection tests for parasitic diseases in the

United States are now performed in several commercial laboratories:

Focus Technologies, Mayo Medical Laboratories, Parasitic Disease

Consultants, Quest Diagnostics, and Specialty Laboratories. Only a

few commercial kits are available in the U.S. for antibody detection

of parasitic diseases. Consequently, the majority of tests performed

at the commercial labs and at CDC use reagents which are not

universally standardized and are produced and evaluated in-house.

This has often resulted in discrepant results obtained by different

laboratories due to different reagents. There is no external

Proficiency Testing program for any parasitic diseases except

Toxoplasma. If an unexpected result occurs, have the sample retested

in another laboratory to confirm the result before accepting it as valid.

 

Immunodiagnostic testing for parasitic diseases is complicated by the

general assumption that serology tests for a disease will detect all

infections caused by any of the species that infect humans. That

assumption is not true; some serologic tests, such as those for

schistosomiasis detect only species-specific antibodies. The same

specimen can have a negative result in one test and a positive result

in another. For example, samples of serum, stool, and urine from a

patient suspected of having schistosomiasis were submitted for testing

to a commercial lab. Although the serum was reported as antibody

negative and the stool exam as no parasites found, the urine exam

revealed eggs of Schistosoma haematobium. The serum specimen was

submitted to CDC for blind retesting and was immunoblot positive for

S. haematobium and immunoblot negative for S. mansoni. In this

situation, tests for schistosomiasis in the two labs were not equal in

detecting the 3 schistosome species that infect humans, with the

potential result of an inaccurate immunodiagnosis.

 

For most parasitic diseases, the antigen is generally the assay

component which has the most influence on test sensitivity and

specificity. Parasites generally have more than one life cycle stage

which may have both mutually shared antigens and stage-specific

antigens. The matrix to which antigens are bound for use in a

specific procedure also physically selects for which antigen subset

will be available for antibody binding. The decision as to which

parasite stage and antigen preparation will be used in a specific

assay should not be made without extensive review of the published

literature. Evaluation of a procedure should be made with specimens

from patients in whom parasites have been observed. Unfortunately,

this is not possible for diseases such as toxoplasmosis, toxocariasis,

or trichinosis because the parasites are sequestered in muscle or

organ tissues and are generally not detectable. Specimens from

well-defined clinical cases are acceptable for assay evaluations of

these diseases, but are usually difficult to obtain. The patient

specimens should be characterized to suit the particular disease.

Sensitivity of a procedure may be affected by the stage and type of

the patient's disease. For example, patients who have undergone

surgery for an echinococcal (hydatid) cyst in the liver almost always

will have detectable antibodies, but may have been negative prior to

surgery. A test evaluated with only post-surgery case specimens will

have close to 100% sensitivity, but a test evaluated with pre-surgery

case specimens will have a lower sensitivity more indicative of how

efficient the assay is as an aid to establishing a diagnosis prior to

surgery. Duplication of a published procedure does not necessarily

mean that the results of several laboratories are identical without

comparable evaluation and, ideally, exchange of reagents and sera. An

organized, impartial proficiency program for parasitic serology assays

other than Toxoplasma does not exist to aid in determining

comparability between tests and laboratories.

 

 

Antibody Detection Tests Offered at the CDC

 

Disease

 

 

Organism

 

 

Test

 

Amebiasis

 

Entamoeba histolytica

 

 

Enzyme immunoassay (EIA)

 

Babesiosis

 

 

Babesia microti

Babesia sp. WA1

 

 

Immunofluorescence Assay (IFA)

 

Chagas disease

 

 

Trypanosoma cruzi

 

 

IFA

 

Cysticercosis

 

 

Larval Taenia solium

 

 

Immunoblot (Blot)

 

Echinococcosis

 

 

Echinococcus granulosus

 

 

EIA, Blot

 

Leishmaniasis

 

 

Leishmania braziliensis

L. donovani

L. tropica

 

 

IFA

 

Malaria

 

 

Plasmodium falciparum

P. malariae

P. ovale

P. vivax

 

 

IFA

 

Paragonimiasis

 

 

Paragonimus westermani

 

 

Blot

 

Schistosomiasis

 

 

Schistosoma sp.

S. mansoni

S. haematobium

S. japonicum

 

 

FAST-ELISA

 

Blot

 

Strongyloidiasis

 

 

Strongyloides stercoralis

 

 

EIA

 

Toxocariasis

 

 

Toxocara canis

 

 

EIA

 

Toxoplasmosis

 

 

Toxoplasma gondii

 

 

IFA-IgG, EIA-IgM

 

Trichinellosis (Trichinosis)

 

 

Trichinella spiralis

 

 

EIA

 

Serology tests for the following diseases or organisms are not

available at CDC, but may be available elsewhere within the United

States or abroad:

 

* African trypanosomiasis

* Ancylostoma

* Angiostrongylus

* Anisakis

* Baylisascaris procyonis

* Clonorchis (Opisthorchis) sinensis

* Echinococcus multilocularis

* Fasciola hepatica

* Filariasis

* Gnathostoma