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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5512_Библиотеки_им_академика_М_И_Перельмана.pdf
Laboto Diagnosis of Mycoc Infections
Jsn
imal hito Concentrans
ents
A new method for determining the minimum inhibitory concentration of antifun
against Candida species is now available (Trek Diagnostic Systems). The method can be
applied in testing a panel of dierent drugs by using plastic plates with wells. Colour reaction
in the well indicates the dilution representing the MIC for the drug tested.
g
al a
g
Conclusion
Antifungal susceptibility testing is now increasingly and appropriately used as a routine
adjunct to the treatment of fungal infections. Guidelines for the use of antifungal testing
and other laboratory studies have been developed. Selective application of antifungal
susceptibility testing coupled with broader identication of ngi to the species level should
be proved useful, especially in difcult-to-manage fungal infections. Future eorts will be
dedicated to further validating the interpretive breakpoints for established antifungal agents
and developing them for newly introduced systemically active agents.
REVIEW QUESTIONS
1. What are the basic dierences between the morphological characters of bacteria and
mycotic agents?
2. What is the signicance of direct microscopic examination?
3. Describe the process of laboratory diagnosis for the following clinical conditions:
Moniliasis, Histoplasmosis, Mycotic meningitis, Ringworm infection, Aspergillosis,
Coccidioidomycosis, and Sporotrichosis
4. An old patient with suspected pulmonary mycosis was subjected to laboratory investi
gation. Which mycotic agents should be sought in his/her sputum specimen?
5. Correlate the mycotic agents with the following laboratory observations: positive germ
tube test, positive urease reaction, presence of spherules, tuberculated macroconidia in
laboratory cultures, presence of pseudohyphae, Wood's light positive, terminal chlam
ydoconidia, presence of rhizoids.
6. When would you apply India ink preparation technique?
7. Which of the mycotic agents are characterized by the presence of arthroconidia? What
precautions are required for the handling of the laboratory culture of Coccidioides
immitis?
8. Name the commonly used media for the culture of parasitic fungi.
9. Discuss the current developments in the laboratory diagnosis of mycotic infections.
Chapter
Laboratory Diagnosis of Parasitic Infections
nai L Mukherjee and Piyali Basu
22
Laborato Diagnosis of Parasitic Infections
J679
I
Medical Laborato Technology: Volume 2
Classifican
ectoparasites
Life le
denitive host
intermediate hosts
reservoir host
Laborato Diagnosis of Parasitic Infections
an uninfected host. A biological vector is a host essential to the life cycle; for example the
biologic vector for Plasmodium is the mosquito. Mechanical vectors transmit the parasite
mechanically. For example, ies that land on infected faeces can then land on food and carry
infective parasite stages from one site to another.
Parasites are only found where the appropriate hosts, vectors or animal reservoirs are
available to allow the organism's life cycle to develop and be perpetuated. Environmental
factors, such as humidity and temperature, are important to the survival of most parasites,
especially those that require arthropod vectors. Temperature extremes and dry conditions
are often detrimental to parasitic forms. Therefore, the majority of parasites are found
in temperate to tropical climates. Unsanitary conditions also contribute to the spread of
organism.
In clinical terms, the infective stage of the parasite is its asexual phase where it multiplies
and gets ready to pass on to new hosts. As the adult form of a parasite cannot be located
easily (found in mosquitoes), the disease is diagnosed by examining the blood smear
of humans which is the intermediate host of the parasite. The parasite is harboured by
humans and found in red cells. Thus by examining the blood smear, the parasite can be
identied and the patient can be treated properly. So the identication of asexual form of
a parasite in human becomes the diagnostic stage in its life cycle. Knowledge of the in
fective stage is also required to understand how to prevent transmission. Sometimes the
diagnostic stage and infective stage are the same, particularly for the intestinal parasites.
For example, in the life cycle of Giardia, the cyst is the infective stage and it is also the
diagnostic stage.
The following are some of the common parasitic diseases, their causal agents and transmis
sion routes.
Common diseases
Causal agents
Transmission route
-
Absolute immunity to parasites is rare unless the individual host is unsuitable for
the parasite to thrive. In general, resistance to parasitic infection increases with age
and exposure to the antigen causing the disease. As with other organisms (viruses and
bacteria), a parasitic infection usually stimulates an immune response against the
I
serum antibody Toxoplasma.
Medical Laborato Technology: Volume 2
ention of Parasi fecon
Blocking of transmission
understand the life history of the parasite,
mosquito control
measures
Susceptib and eatment
(immunocompromised)
Toxoplasma Cptosporidium
Treatment
tentative diagnosis
denitive diagnosis
endemic areas
Laborato Diagnosis of Parasitic Infections
Handling of Specimens
endemic areas;
clear patient instructions
Stool Specimen
physical examination of stool trophozoites cysts.
TABLE 22.1
Amoebic dysentery stool
Steatorrhoea stool
Vaginal discharge
Non-pathogenic
Common ptozoan infecons in humans and specimen quired for laboto diagnosis
urogenital swab
(stool)
Entamoeba histolytica
Giardia lamblia
ichomonas vagina/is
ichomonas hominis, Entamoeba coli, damoeba
butschli, Entamoeba hartmanni, Endolimax nana
Direct wet mount saline wet mount
trophozoites
Preserved specimens
Cysts
Cysts
Medical Laborato Technology: Volume 2
Coecn and ocessing of Faecal Specimens
■
Giardia)
■
■
■
■
Laborato Diagnosis of Parasitic Infections
three stool specimens
Preservan and Transport of Faecal Specimens
preserved for future examination
preservatives,
xatives,
preservatives
Reagents
A. Formaldehyde solution (10%)
Caution:
686
Medical Laborato Technology: Volume 2
B.
Caution
Preparation
Preparation
°
Note
Procedure to make working solution of PVA ative
°