Laboratory #1

INTRODUCTION TO THE

      PARASITOLOGY LABORATORY

 

Objective:

The purpose of this first laboratory is to introduce you to some of the techniques that a veterinarian uses to detect the eggs, cysts, and larvae of parasites in the feces of animals. The examination of blood for parasites is also described in this handout, although you will not be doing this procedure today. Since most of the diagnostic stages of parasites are microscopic, the proper use of your microscope is very important. Therefore, a section of this handout covers the proper use of the microscope and gives some suggestions as to correcting some common problems.

Before you leave the lab check the CHECKLIST OF OBJECTIVES FOR LABORATORY 1 to be sure you have done and seen everything that is required.

            Laboratory Exercises:

 For the DATA SHEET to record your results and for the results of the Class: click here

A. Use of the microscope for fecal exams:

The following tips will help you adjust to using your microscope for the examination of fecal samples for parasites.

1. The first thing to remember is, unlike a histological section, a wet-mount of parasite eggs is three-dimensional and, therefore, you may find that you must continually adjust the focus to see objects at the bottom or top of the wet-mount.

2. Make sure you have the condenser iris diaphragm open so that there is just enough light to work with (the higher the aperture, the lower the contrast). When using the 4X and 10X objectives, the diaphragm should be almost closed; open it a little for use with the 40X objective and further for use with the oil lens.

3. The condenser should be moved to almost its top position (you should not be able to see the lamp filament). Do not use the condenser to adjust the light level, use the diaphragm.

                    4. Also check out the page on Proper use of the Microscope.

B. Examining a wet-mount:

When examining a wet-mount for cysts and ova, start in one corner of the coverslip using your 10X objective and cover the slide in overlapping fields (see diagram #1). Use your 40X lens to examine any suspicious objects, and after you have completed the examination, repeat about 1/4 of it using the 40X objective to find the smaller cysts. Note that the addition of a drop of iodine to the sample will stain many eggs and cysts increasing their contrast.

DIAGRAM #1.

 lab1-1.jpg (52085 bytes)

C. Fecal examination techniques:

In order to get the best results from your examination of feces for evidence of parasitic infections you should follow the guidelines presented on the page entitled: COLLECTION AND PROCESSING OF FECES FOR PARASITOLOGYalso check out Table 1 for a comparison of the various techniques.

To help you determine if what you see during a fecal exam is parasitic, I've made a page showing the various non-parasitic artifacts and pseudoparasites that will be found in feces.  Check out the Artifacts page to avoid some of the more common non-parasites.

In today’s lab you should do the following techniques, making use of the 2 samples of dog feces under the hood. (This feces contains eggs of nematode parasites.) Record your results (# of eggs per coverslip) on the DATA SHEET  and submit it through this web site by Monday at noon.

1. Saturated salt flotation - There are numerous devices for doing this type of flotation now in use in local veterinary hospitals. Several manufacturers have donated devices for your use and we will be using them throughout the course in order to allow you to become familiar with each type. Today we will use one of these devices (see instructions on the saturated salt flotation page). Use this technique on sample "A".

2. ZnSO4 Centrifuge Flotation Technique.   Use this technique to run both sample "A" and "B".

3. Ethyl Acetate sedimentation - Use this technique to run both sample "A" and "B".

4. Direct Smear - Use this technique on sample "A".

In a future laboratory you will learn how to count the number of parasite eggs per gram of feces using the McMaster slide, which is in your slide box. The use of the Baermann apparatus for recovering larval nematodes from feces is demonstrated in today’s laboratory, you will be using the technique in a future lab.

The methods for examining feces covered in this laboratory are also covered in Foreyt’s "Veterinary Parasitology Reference Manual" pp. 1 - 10, in Sloss and Kemp’s Veterinary Clinical Parasitology" pp. 1 -24.

D. Demonstrations of the taxa to which parasites belong:

Demonstrations are set up in MDL 12 to illustrate the various taxonomic groups to which the common parasites of domestic animals belong. 

Demonstrations are set up in MDL 12 to illustrate the various taxonomic groups to which the common parasites of domestic animals belong. 

E. Review Photos:  These are found in this CAL web site.  Go over them at your leisure.

 

 

            INDEX TO TECHNIQUES

COLLECTION AND PROCESSING OF FECES FOR PARASITOLOGY

SATURATED SALT FLOTATION

ZINC SULFATE (CENTRIFUGE) FLOTATION

ETHYL ACETATE SEDIMENTATION

DIRECT SMEAR

BAERMANNIZATION

STOLL EGG COUNTING TECHNIQUE

McMASTER EGG COUNTING TECHNIQUE

MODIFIED WISCONSIN SUGAR FLOTATION TECHNIQUE

BLOOD PARASITE PROCEDURES

PROPER USE OF THE MICROSCOPE

 

CHECKLIST OF OBJECTIVES FOR LABORATORY 1

1. Use of the microscope for examination of fecal floats.

2. How to do a direct smear (advantages and disadvantages).

3. Use of the commercial device (and in future labs the use of the other commercial devices). (Advantages and disadvantages of the saturated salt flotation).

4. Zinc Sulfate flotation (advantages and disadvantages), we will actually do this in another lab.

5. How to do an Ethyl Acetate sedimentation (advantages and disadvantages).

6. Demonstration of the Baermann technique. (Know how to run it and under what circumstances it is used).

7. An appreciation of the general characteristics of the various phyla to which parasites belong (i.e. know how to determine if an organism is a protozoan, fluke, tapeworm, nematode or an arthropod).

8. Answer the Review Question at the end of the demonstrations for practice. (Note: The review question is in the same form as the questions asked on the lab exams. There will be a review question at the end of each lab’s demonstrations to give you some practice before the actual exam.)

9. Fill out the data sheet with the results of each fecal examination that you ran and put your data onto the web site: http://cal.vet.upenn.edu/paraav/forms/lab1data.htm.   The results will be tabulated for the class and reported to you in the next lab.