What can you use a drop of to increase the contrast of many cysts and eggs?
- iodine
What diagnostic test is very poor at finding infections with common tapeworms in cats and dogs?
- fecal flotation
- only 1.6% of tapeworm infected cats were positive on a fecal flotation
Do not make a decision to not examine a fecal based only on the presence of....
- clinical signs
- parasites are found at equal rates in animals with and without diarrhea
What are the major problems with the direct wet mount?
- examines only a small amount of feces
- takes a very long time to examine the sample properly
Why is it important to remove or dissolve fat found in feces during a diagnostic test?
- it will float to the top of any flotation solutions used to recover parasites from feces
- a large amount of fat will prevent you from recovering parasite eggs when doing a centrifugal flotation
How can you eliminate/dissolve fat in a fecal specimen when performing a centrifugal flotation test?
ethyl acetate
- dissolves fat found in feces
- b/c ethyl acetate-fat solution is lighter than water, can remove it from fecal sample by centrifugation in water
- eggs in sediment in test tube after fat removal are more concentrated than in original feces
Baermann apparatus
- device used to recover nematode larvae from a fecal sample
- requires live larvae
? feces must be fresh, not fixed, frozen, or refrigerated
- good to use because larvae may be distorted by concentrated flotation solutions
Which common ELISA-based tests detect the presence of the antibody to the parasite?
- feline heartworm antibody test
Which common ELISA-based tests detect the presence of antigen produced by the parasite?
- canine heartworm antigen test
- Giardia antigen test
Blood smear
- used to detect parasites that live in the blood
-
important to get a feathered edge
? difficult to see parasites when RBCs are stacked on top of each other
- normally stained with
Giemsa stain
= mixture of methylene blue & eosin
Protozoa
- phylum
- single-cell animals
- fall into several classes
generally organized by structures used for locomotion
? flagellates (flagellum)
? amoeba (pseudopodium)
? ciliates (cilia)
? coccidia (no structures)
- most are microscopic
Eimeria bovis
-
protozoan
parasite of the intestine of cattle
- diagnostic stage =
oocyst
- passes in the feces & will float in a standard saturated salt solution
Babesia canis
-
protozoan
parasite of dogs within erythrocytes
- measures about 4 um in diameter
- multiplies asexually w/in RBC before eventually lysing the cell ? leads to anemia
- uses a tick as a vector
- diagnostic stage =
trophozoite
Trophozoite
- a growing stage in the life cycle of some sporozoan parasites
- actively absorbing nutrients from the host
Nematodes
- Phylum Nemathelminthes, class
NEMATODA
- cylindrical in shape tapering at both ends
- have a complete digestive system
- body is covered by an acellular cuticle
- helminths (worms) are commonly known as roundworms b/c of the shape of their cross-section
Ascaris suum
- "large roundworm of pigs"
- nematode from the small intestine of a pig
- one of the larger nematodes
- diagnostic stage =
egg
passed in feces
? egg will float in saturated salt solution
? standard fecal flotation can be used to identify an infection
-
k
Platyhelminthes
- phylum
- the "flatworms"
- usually flattened dorso-ventrally and are bilaterally symmetrical
- lack true body segmentation, a body cavity, and an anus
- include:
? trematodes (TREMATODA)
? cestodes (CESTODA)
Trematodes
- P: Platyhelminthes C: Trematoda
- as adults are:
? flattened dorso-ventrally
? have a blind gut
? no coelom
? have suckers for attachment to the host
- commonly known as "flukes"
- many eggs have an operculum (cap) at one end and may not float in standa
Fasciola hepatica
- trematode
- lives as an adult in the bile ducts of ruminants, horses, and other mammals, including humans
- diagnostic stage =
egg
passed in feces
- has an operculum (cap) at one end
-
may not float in standard saturated salt solution
? must use sedimen
Cestodes
- P: Platyhelminthes C: Cestoda
- as adults are ribbon-shaped whose "body" is made up of many repeating segments
- have no digestive tract or body cavity
- adults are always found in some part of the host's digestive tract
- commonly referred to as tapewo
Taenia taeniaeformis
- adult tapeworm is found in the small intestine of cats
- can be up to 60 cm long
- diagnostic stage =
gravid proglottid
which passes in feces
- identification of the type of tapeworm may be made by examining the morphology of proglottid & eggs it contai
Arthropods
- P: Arthropoda
- bilaterally symmetrical
- paired, multi-jointed appendages
- exoskeletons of secreted, non-cellular material
- dorsal heart & ventral nerve cord
- bodies are more or less segmented
- cold-blooded
- importance stems from potential to at a
Arachnids
- P: Arthropoda C: Arachnida
- all characteristics of phylum arthropoda
- share chitinous exoskeleton w/ insects
? have 4 pairs of legs in adult stage
- 2 main groups:
? ticks
? mites
Dermacentor variabilis
- "American dog tick"
- suck blood from hosts & are vectors for several parasitic diseases such as Rocky Mountain Spotted Fever
Insects
- P: Arthropoda C: Insecta
- have all of the characteristics of the phylum Arthropoda
- exoskeletons are composed of chitin & cross-linked proteins
- adult stages have 3 pairs of legs
- bodies are divided into 3 segments
? head, thorax, & abdomen
- three
Mosquito
- a fly (insect) that may act as a vector and intermediate host for several different parasites
Ctenocephalides felis
- P: Arthropoda C: Insecta
- most common flea of dogs and cats
- are laterally compressed, allowing them to more easily maneuver the hairs of their host
- feed on blood as adults
True flies
- have complete metamorphosis
- 4 stages in life cycle
? egg
? larva
? pupa
? adult
- depending on parasitic fly, either or both the adult and larval stages can be parasites
Lice
- have incomplete metamorphosis
- stage that comes out of the egg looks very similar to adult louse
- 2 basic types: chewing & sucking
Sucking lice
- narrow head with recessed stylets for sucking blood
Chewing lice
- have chewing mouthparts to feed on skin, hair, feathers, etc.
- 2 groups based on antennae
Ischnocera
? have antennae that stick out from the side of the head
Ambylcera
? have antennae recessed into grooves at the side of their head
? many chewing lice
Fleas
- have complete metamorphosis
- only the adult flea is parasitic
- Ctenocephalides felis = most common flea of dogs and cats
? laterally compressed
How do you run a passive fecal flotation using a commercially available test?
- lift cap & remove green insert
- insert bottom of green insert into feces to collect sample & return into fecalyzer
- lift cap & fill w/ fecasol or saturated salt or whatever fluid of choice up to the bottom of the arrow on the side of the vial
- turn c
How do you run a centrifugational fecal float?
- fill a 15 ml centrifuge tube w/ ZnSO4 solution & pour into specimen cup
- use a tongue depressor to squish 2-5 g of feces through a strainer into the ZnSO4 solution in the cup
? make sure the sieve is actually in the liquid
? the more feces you use, the
Pro-tip to increase sensitivity of centrifugational fecal float?
- use more feces OR
- after centrifugation, fill tube w/ ZnSO4 to form meniscus, place coverslip on top, and wait 10 min
? add a drop of iodine to microscope slide and then place coverslip on top
? removes need for using the loop
How do you make a wet mount slide?
- place a small amount of feces on a microscope slide
- add a drop of liquid & mix thoroughly
? for liquid feces looking for protozoans, use saline
? for helminth eggs & protozoan cysts, use saline, water, or iodine solution
- cover w/ cover slip & move a
When should you use a wet mount?
- liquid feces where protozoan parasites may be present
- fecal samples where amount obtained is too small to handle any other way
- as an adjunct to flotation for eggs that don't float
? best way to do this is to run ethyl acetate sedimentation and then
How should feces be collected for examination?
- should be processed as soon as possible after passage from animal
- ruminant & horse feces can be collected in airtight containers to prevent desiccation during transport
? ziploc with air removed works fine
Why do you want to store feces in an airtight container?
- keeps it anaerobic & prevents eggs from developing and potentially hatching
How can you store feces if you can't examine it immediately?
- refrigerated (NOT FROZEN) for a few days
? not recommended for Baermann
- fixed
? 10% formalin, or 5% formalin-saline for protozoan cysts
? add to feces at a ratio of 3:1 (volume) & mix well
- horse & ruminant samples collected in a ziploc can be stored
How should you approach feces of an animal that has been treated with antidiarrheal preparation?
- preps containing bismuth, kaolin, mineral oil, or oral contrast material can make parasites difficult or impossible to find
- repeat fecal 5-10 days after withdrawal of treatment
How should you process feces?
- first examine for consistency, frank or digested blood, and other clinical signs including motile tapeworm segments
- run test of choice
When should you repeat fecal exams?
- clinical signs suggest parasitism, but initial fecal is negative
? may be prepatent, or patent w/ low numbers
? repeat in 2-3 days, repeat again w/in 7-10 days
? 3 tests detect >95% of infections
- following specific therapy for a parasitic infection, h
What is the best use of a ZnSO4 centrifugational float?
- only way to find Giardia cysts
- very good technique for Trichuris
- will most of the time recover nematode larvae
- generally a good choice
Which types of eggs might not float in a ZnSO4 centrifugational float?
- Trematode
- Pseydophyllidean
-
Physaloptera
Problems with a ZnSO4 centrifugational float?
- nematode larvae can be crenated
- protozoan cysts can be crenated
What is the best use of a saturated sugar centrifugational float?
- = gold standard for fecal examinations
? higher specific gravity floats more eggs
What is the reason you would use a ZnSO4 centrifugational float over a saturated sugar centrifugational float?
- if you're looking for Giardia
- sugar one causes them to crenate beyond recognition
What is the major problem with a passive float?
- misses Giardia most of the time
What is the major benefit of a passive float?
- easy, quick
- doesn't require a lot of feces
- efficient
When should you use an ethyl acetate sedimentation?
- best for examining samples with lots of fat in them
- also good to look for trematode or cestode eggs
What is the problem with ethyl acetate sedimentation?
- takes a long time
- can be expensive
When should you use Baermann technique?
- to look for live nematode larvae for identification
What is the problem with the Baermann technique?
- takes a long time to examine
- only recovers live larvae
? have to use fresh feces
When should you use a direct wet mount?
- liquid feces when protozoal trophozoites are suspected
- used in adjunct w/ a flotational technique to find eggs that do not float
When should you use an ELISA test?
- when looking for a specific parasite whose diagnostic stages may be below the level of detection otherwise
- can have false negatives & positives, so take whole case into account and possible confounding factors
When should you use a PCR-based test?
- pretty much when you know what you're looking for
- only useful if parasite's DNA is in the sample you're using