The document discusses the diagnosis of parasitic zoonoses through clinical and laboratory methods. Clinical diagnosis can establish the condition in endemic areas based on characteristic signs, but is often hindered by vague or late symptoms. Laboratory diagnosis relies on parasitic diagnosis using direct examination of samples to detect parasites, and concentration/culture if needed. Immunodiagnosis detects antibodies or antigens in serum, and is useful for chronic, asymptomatic or low parasite load cases. Many serological tests exist but have limitations, while antigen detection offers advantages. Skin tests are also used but lack standardization. Overall laboratory diagnosis plays an important role in establishing the specific cause and supplementing clinical findings.

1. DIAGNOSIS OF PARASITIC
ZOONOSES

2.  The diagnosis of parasitic zoonoses
rests on both the Clinical and
Laboratory diagnosis of the condition.

3. CLINICAL DIAGNOSIS
 In areas where the disease is endemic ,diagnosis of
the condition may be achieved by the characteristic
clinical presentation of the disease.
 However, in most of the cases the clinical diagnosis is
hindered by less manifestations of the characteristic
clinical signs,by their late development, Lack of
specificity ,or occurrence of asymptomatic carries.
 In non-endemic areas where the parasitic diseases are
relatively uncommon ,clinical diagnosis of the condition
is frequently more difficult.
 Therefore,the laboratory diagnostic methods play an
important role in establishing the specific aetiological
diagnosis of the disease and/or supplementing the
clinical diagnosis of the condition.

4. Laboratory Diagnosis:
The laboratory
diagnosis of parasitic infections broadly
rests on the Parasitic diagnosis and
Immunodiagnosis.

5. PARASITIC DIAGNOSIS
 The definitive diagnosis depending on the nature of
the parasitic infection, is based on
 Demonstration of the parasites in the
Faeces,Urine,Sputum,Blood,Cerebrospinal
fluid(CSF) and Other body fluids.
 The parasites are demonstrated in the specimen
conventionally by the direct wet smear methods
(e.g.,wet blood film for microfilariae),stool smear (for
protozoan cysts and trophozoites and the helminthic
ova and larvae).

7. If these methods fail to reveal the parasites,
 The Concentration methods
●Haemo-concentration for
haemoprotozoan,microfilariae,
● Stool concentration for protozoan cysts and
helminthic ova),
 Culture (e.g., blood culture in NNN(Novy-MacNeal-Nicolle
medium) for Leishmania, stool culture in NIH media for
Entamoeba histolytica, coproculture for larvae of intestinal
helminths etc.
 Animal inoculation (e.g., isolation of Toxoplasma by
intraperitoneal inoculation of MICC(Mineral-insulated
copper-clad cable)) and
 Xenodiagnosis (e.g., trypanosomaisis) of the appropriate
specimen are usually considered to be valuable aids in the

9. The parasitological methods in addition to
establishing specific diagnosis of the condition, have the
advantages of being relatively simple,economical and
can be performed with ease.
The methods are widely used for diagnosis
of the cases as well as for epidemiological studies in a
few parasitic infections.

10. However, the parasitological methods are of limited
use in the diagnosis of :
1) hydatid disease or larva migrans, in which the
developmental stages of the parasites are not
excreted in the body fluids,
2) Toxoplasmosis and many other parasitic infections,
in which the developmental stages are
demonstrated with difficulty and
3) pre- patent or chronic infections, showing less
number of parasites in the body fluids and also in the
survey of parasitic infections of low incidence.

11. IMMUNODIAGNOSIS
The conventional parasitological
methods often fail to direct the chronic cases or carriers
where the parasite load is very less or the parasites
lodged in tissues of the host.
In these situations the immunological
methods are widely used for the diagnosis of individual
cases as well as for the epidemiological studies.
Therefore, the immunological tests are
particularly useful to diagnose asymptomatic or latent
parasitic infections, as well as in some chronic parasitic
infections.
The seroepidemiological studies help
to assess the prevalence of the disease and to select the
population for future vaccine trial in a parasitic infection.

12. The immunodiagnostic tests
largely detect the circulating specific antibodies and
less frequently circulating antigens in the serum,
CSF and other body fluids. The skin test and less
frequently other parameters of the cell mediated
immunity (CMI) in vitro are also used in the
immunodiagnosis of certain parasitic infection.

13. Serological Method:
A variety of serological methods
have been developed for detection of specific
circulating antibodies in most of the parasitic
infections.
These include indirect
immunofluorescence antibody (IFA), indirect
haemagglutination (IHA), complement fixation(CF),
bentonite flocculation(BF),latex agglutination (LA),
double diffusion-in-gel (DD),precipitation test,counter-
current immunoelectrophoresis (CIEP),dye test,
enzyme linked immunosorbent assay (ELISA), radio
immunoassay(RIA) and many other tests.
The specificity and
sensitivity of these tests determine their usefulness in
a diagnostic laboratory.

14. But these tests, based on the
demonstration of antibodies, are limited by their inability
to differentiate between the recent and past infection
and assess the degree of parasitic infection.
These tests are also unreliable or
inconclusive in the patients undergoing
immunosuppressive therapy, having underlying
diseases and in the diagnosis of congenital parasitic
infections (e.g., congenital toxoplasmosis).

15. The tests modified to detect specific IgM
antibodies have been employed recently in many
parasitic infections to diagnose acute and congenital
infections.
The demonstration of specific circulating
IgM antibodies by IgM-IFA is diagnostic of congenital
toxoplasmosis, because IgM antibodies from the
mother do not cross placenta to reach the foetus.
Recently,countercurrent
immunoelectrophoresis(CIEP),reverse IHA,ELISA,etc.
have been employed to direct the circulating parasitic
antigens in the serum,CSF,urine,faeces and various
other body fluids to diagnose
amoebiasis,toxoplasmosis,filariasis,hydatid disease and
many other parasitic infections.

16. The antigen detection in the
serum or other body fluids offers many advantage
over the traditional methods of antibody detection.
These methods are useful for
early detection of the cases,diagnostic indicator to
assess the degree of parasitic infection in the patients
receiving chemotherapy.
The detection of antigen is
reliable in establishing the diagnosis of parasitic
infection in patients receiving immunosuppressive
therapy or with underlying diseases with suppressed
antibody responses.

17. The combination of
circulating antigens with antibodies to form immune
complexes and the intermittent rupture of the
parasitised cells in certain parasitic infections
(e.g.,toxoplasmosis) are the potential hindering
factors against the successful demonstration of the
antigens in the serum.
Similarly,demonstration of the
antigen in the biopsy specimens or body fluids(e.g.,
urine,faeces,CSF,etc.) is also feared to be relatively
less sensitive and less practicable for routine use in
a laboratory.

18. SKIN TESTS
A wide variety of skin tests are employed
due to their low cost, simplicity of the procedure and
rapid results, in the immunodiagnosis of a wide variety
of parasitic infections
But due to their several inherent
disadvantages (lack of standardised antigen,difficulty in
standardisation and unifornity of the test, lack of
specificity and variation in the reactivity of the host),the
skin tests are of limited value in the diagnosis of many
parasitic infections.

19. The intradermal skin tests are broadly of two
types:
i) immediate hypersensitivity type and
ii) delayed hypersensitivity type.
The former is employed routinely in the
immunodiagnosis of helminthic infections and
the latter in the diagnosis of protozoan
infections including amoebiasis, leishmaniasis,
trypanosomiasis and toxoplasmosis.

21. Problems in Immunodiagnosis of Parasitic Infections
The non-availability or difficulty in the
availability of the parasitic antigens, difficulty in the
standardisation of the antigens and high-cost
technology dependent immunoassays are the problems
associated with the immunodiagnosis of the parasitic
infections.
1) Non-availability or Difficulty in
Availability of parasitic antigens :
The culture of parasites in vitro
(e.g., culture of Entamoeba histolytica in Diamond’s
medium),certain developmental stages of the parasites
obtained from infected cases (e.g., microfilariae in the
blood,eggs of Schistosoma haematobium in the
urine,etc.)

22. Or the parasites maintained
in laboratory animals (e.g., tachyzoites of
Toxoplasma gondii maintained intraperitoneally in
mice) are the routine sources of different parasitic
antigens for their use in a variety of
immunodiagnostic tests.
The different preparations of
parasitic antigens are used in the immunological
testes.
These are either whole,
particulate or crude extracts of the parasites (e,g.,
Leishmania, Trichinella and many others),

23. Semi-purified (e.g.,
Trypanosoma, Echinococcus, Schistosoma and
others) or purified (e.g., Trypanosoma,Schistosoma
and others) preparations of the antigens.
However , in majority of infections the antigens
are difficult to obtain, primarily due to the lack of
suitable experimental animal model and the non-
availability of in vitro culture methods for the
cultivation of various parasitic agents.

24. 2) Standardisation of Antigens:
The non-availability of adequate
quantities of parasitic antigens creates difficulty in the
standardisation of the antigens.
The local variations in the
preparation of antigens and other reagents are the
practical difficulties, which may interfere with the
reproducibility of the test and makes interpretation of
the test results difficult.
At present, standards for
diagnostic antigens are available only in a few
parasitic infections.

25. 3)High Cost Technology:
A wide variety of tests are
available in the serodiagnosis of parasitic infections, in
line with recent developments in immunology.
However, many of these tests
which are highly sensitive and specific,nevertheless
depend upon high cost technology.
The limitation of IFA,ELISA and
RIA are that these tests can be carried out only in the
laboratories equipped with expensive, sophisticated
apparatuses like fluorescent microscope ( for IFA)
gamma counter (for RIA) and spectrophotometer (for
ELISA).

26. Hence, there is a need for
simple, rapid and yet sensitive and reliable diagnostic
tests for small laboratories and in the field engaged in
the diagnostic of zoonotic parasitic diseases.
In addition to the existing
simple assays such as direct agglutination of the
parasite, latex agglutination tests, etc. recently many
other simple tests such as, India ink
immunoassay(toxoplasmosis), direct agglutination test
(leishmaniasis) have been staphylococci adherence
test (amoebiasis)have been developed and evaluated
for use in the diagnosis of many parasitic infections at
the field level and small laboratories.
Currently, direct card
agglutination test (CAT) is being used with success in
the surveillance of African trypanosomiasis.

27. Availability of the technical
expertise, equipments and other facilities to perform
the test, volume of the specimen to be processed
and the requirements of field surveys, all contribute
towards the selection of an immunodiagnostic test,
to be carried out in a particular laboratory.
New avenues for serodiagnosis
of parasitic infections are expected to result from the
use of monoclonal antibodies and DNA probes.

28. The monoclonal antibodies produced against a veriety
of parasitic antigens have been used for the
identification, purification and characterisation of
relevent antigens and reagents in the
immunodiagnostic tests.
The DNA probes have
been used successfully in the diagnosis of several
infectious diseases and are at experimental stage for
use in the diagnosis falciparum malaria and a few
other parasitic infections.