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Diagnosis of Parasites
Terms in this set (14)
Skin - itchy, redness, hairloss, flakiness.
Heart/Lungs - coughing, exercise intolerance.
GI - diarrhea, skinny or wt.loss, tarry or bloody stool, poor hair coat.
1. Flashlights can be very useful in searching for these parasites. Large slow moving ectoparasites eg. lice, ticks and possibly fleas, can be collected with forceps or fingers.
2. Winged bloodsucking insects can be collected using a simple suction tube or vacuum cleaner fitted with an in-line filter or a chloroform tube placed over the parasite. Lice and occasionally fleas may be caught by this method.
3. Examination of hairs can reveal nits (louse eggs).
4. Preserving large ectoparasites for shipping (eg. ticks, fleas, lice). Specimens should be submitted in vials or sealed plastic bags with paper towels soaked in preservative. The preservative of choice is 70% alcohol. The fixative, 10% formalin, should not generally be used.
Colour - if hookworm may have tarry stool. If whipworm may have mucus and frank blood. Float - often Sodium Nitrate - cheap. May destroy giardia. Zinc Sulfate better for giardia. Float doesn't work for trematodes, cestodes. Ovassay or Fecasol is test of choice. Use direct smear for giardia or for coccidia - stain.
Collection and Handling of Fecal Samples.
- Preferably, fecal samples should be collected from the rectum. If material is collected from the ground it should be from the top of a freshly passed deposit. Avoid deposit areas in contact with the ground.
- A minimum sample size is 5 g. Preferably submit a "golf-ball" size sample in a plastic bag or a container that is air-tight and water-tight.
- Store the specimens in a refrigerator until examination or shipping. DO NOT FREEZE FECAL SAMPLES.
- Most parasites (excepting some protozoans) will still be detectable and easily identifiable in fecal samples examined 2 to 3 days after collection, if the samples have been refrigerated (4oC) in the meantime.
Feces, Direct Smears
These can be made by transferring a small sample of feces to a glass slide. Mix in a small amount of saline. Drop on a coverslip and examine directly under the microscope. This technique will reveal heavy infections of eggs and cysts and may detect helminth eggs and larvae or protozoan which typically do not float and therefore are not detected with standard fecal flotation techniques.
Feces, Visual Examination
Search macroscopically for large gravid segments of cestodes (eg. Dipylidium caninum in dog and cat feces) or whole adult helminthes.
This technique will separate from feces, various species of helminth eggs, and protozoan cysts (eg. Giardia canis cysts in dogs). Some helminth eggs, nematode larvae and protozoan (Giardia canis) generally are not detected with this technique. If infection with any of these parasites is suspected a direct smear technique should be requested.
Canine Heartworm (Dirofilaria immitis)
Microfilaria I.D. (Knotts Test for Microfilaria Detection) The Knotts Test is used to detect and identify circulating microfilaria of Dirofilaria immitis. It can detect infected dogs as early as 6 months post-infection. Draw off at least one to 3 ml of venous blood into a vial containing an anticoagulant eg. heparin or EDTA. Mix the blood and anticoagulant. Store sample overnight at room temperature. Submit the sample to the diagnostic laboratory the next day. Approximately 25-33% of the heartworm infected dogs will not be detected with this test.
Occult Heartworm Antigen Test. This test is an ELISA serologic test that detects circulating adult worm antigen. Submit at least 1 ml of either plasma or serum. The test detects infected dogs as early as 6.5 months post-infection (most reliably at 8 months p.i.). If only one heartworm test is to be done (Knott's vs. Antigen Test), the antigen test is preferable to the microfilaria test.
- Skin Scraping
Use #10 scalpel blade with mineral oil on the blade and on the skin. Best area is periphery of lesion. Scrape until capillary bleeding. For demodex should squeeze skin first to express the mites.
- Scotch tape to animal, then to slide.
- Or comb out debris or flakes.
Skin Scrapings, Mange Mites
1. For lesions with minimal epidermal hyperplasia and lesions caused by deeply burrowing mites (eg. Sarcoptes) or in hair follicles (eg. Demodex). Dip a scalpel blade in mineral oil or glycerine. Using the blade, scrape the periphery of the lesions at right angles to the skin until pinpoint haemorrhaging occurs. The sample should be pink in colour. Examine under a microscope.
2. For lesions with marked epidermal hyperplasia and lesions caused by lice and superficially dwelling mites. Scrape the dried exudate and debris into a small ointment tin using the lid as a scraper.
3. Ear mites (eg. Otodectes) can be found easily with an otoscope. They can be removed from the external ear with a cotton swab.
4. Some surface feeding mites (eg. Cheyletiella) in dogs and other hosts can be collected by vigorously brushing the host over a plastic sheet. Mites and debris will accumulate on the sheet and can be transferred to a container.
The majority of internal parasites are diagnosed by microscopic examination of the feces for eggs that are released by the adult female in the pet's intestine. The number of eggs released in a given fecal sample can be variable, sometimes there aren't any even though the pet has an adult female parasite in its intestines. This means that a negative fecal report does not guarantee that the pet is free from internal parasites. In many cases it is necessary to run numerous samples to assure that the pet is free of internal parasites.
The two primary methods of fecal analysis are direct observation and fecal flotation.
In direct observation a smear is made of some fecal material on a microscope slide and the slide is analyzed for parasite eggs. It is used to detect eggs that don't show up well during the fecal flotation.
Fecal flotation is the most accurate way to detect most internal parasites. A sample of fresh feces is put into a special solution that causes any eggs that might be present to float to the top and adhere to a cover slip. The cover slip is put on a microscope slide for analysis. This concentration of eggs substantially increases the chance of finding any eggs that might be present. Some eggs, notably Tapeworm eggs, dissolve during this process and might be undetected. This is the reason you can see Tapeworms in the pets stool yet the fecal analysis came back negative.
Once a fecal sample is obtained it should be kept cool until it is analyzed. Analysis should be within 12 hours to increase accuracy.
A. The flotation solution has been added to the fecal container and a cover slip has been placed on the top to collect any eggs that float to the surface after a 5 minute wait.
B. The cover slip is put on a microscope slide and carefully scanned for the eggs of any parasite.
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