Term
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Definition
| – it will cause small globular arthrospores attached to the hair shafts to be visible if positive, |
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Term
| List the 4 most common dermatophytes (genus and species) that affect dogs and cats. |
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Definition
The most common fungus isolated from dog and cat fur is Microsporum canis, followed by M. gypseum and Trichophyton
mentagrophytes |
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Term
| List the 3 common genera of dermatophytes that affect animals. |
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Definition
The three genera involved are Microsporum, Trichophyton and
Epidermophyton; the first two are most frequently found in animals while the third causes problems mainly in humans |
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Term
| . What yeast organism is commonly seen in cases of otitis externa and often as a secondary organism on atopic patients skin? |
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Definition
| Malassezia pachydermatis – has a characteristic oval peanut-shaped form |
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Term
| List the steps for an ear swab sample |
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Definition
Slide prep:
Position 2 or more microscope slides on a clean surface
Place a drop of mineral oil on one of the microscope slides
Roll the cotton end of one of the applicators in the mineral oil on the slide and leave it in place, so it is ready to be used when collecting a sample.
Collection:
With the free hand, introduce one of the cotton-tipped applicators into the vertical ear canal and collect a sample
1. hold the applicator vertically
2. insert the applicator to the depth of the vertical ear clanal – never further into the ear canal than you can see.
3. rotate the cotton-tipped applicator
4. remove the applicator
collect a sample with the dry applicator first and the mineral-soaked applicator last.
If the vet requests a sterile swab for culture and sensitivity, this should be performed prior to inserting a cotton-tipped applicator into the ear canal
Slides:
Using a graphite pencil, label the microscope slides with patient identifiers. Include the animal and client name, and either “right ear” or “left ear”.
Transfer the specimens to the slides:
1. roll the dry applicator on the surface of one or more dry slides
2. roll the mineral oil soaked applicator on the slide with mineral oil
3. break up or remove large chunks of exudates from the slide with the applicator
4. place a coverslip over the sample from the mineral oil-soaked applicator
for suspected bacteria or yeast infxns, stain the dry slides as needed for cytologic exam |
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Term
| . Describe the appearance of a Malassezia organism. |
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Definition
| Malassezia pachydermatis – has a characteristic oval peanut-shaped form |
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Term
| What should a normal ear swab sample contain? |
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Definition
| Simple cornified squamous epithelial cells with no evidence of inflammation and few microorganisms |
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Term
| Which fungal organisms fluoresce under a Wood’s lamp? Do all cases infected with Microsporum canis fluoresce? |
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Definition
A Woods light can sometimes help identify good candidate sample areas according to their fluorescence, but dermatophyte infxns do not always fluoresce. Likewise, any fluorescence may also be unrelated.
Wood’s lamp emits UV light at a wavelength of 330 - 365 nm and is used in a dark room to examine hairs for certain
dermatophytes by shining the light directly on the sample. Microsporum canis and M. equinum show a yellowish-green
fluorescence due to the pteridine secreted by these fungi. Some bacteria
The use of a Wood’s lamp is a useful tool in the small animal clinic, but it has limitations since not all M. canis strains show
fluorescence; some topical preparations mask the fluorescence. Also, if the skin is swabbed with alcohol the fluorescence
may be less intense and there may be a non-specific fluorescence. When using Wood’s lamp, a bright green fluorescence
can be taken as an indication of dermatophytosis, but its absence is not sufficient evidence to rule out this condition since
the dermatophytosis present may be due to fungal species that produces little or no fluorescence |
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Term
| Describe dermatophyte lesions |
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Definition
Dermatophyte lesions, commonly called ringworm since the lesions grow circularly at the periphery, but may be localized or diffuse in their actual pattern. Amount of hair loss is variable.
Typically circular, but can be diffuse as well, according to the following patterns:
Localized lesions:
- distinct, identifiable border
- circular in shape
- thickened skin
- hair loss
- scaly skin
Diffuse lesions:
- vague border
- irregular shape
- hair loss
- scaly skin |
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Term
| List the techniques for collecting samples to examine for dermatophytes |
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Definition
Since ringworm grows outward from the center, it usually makes sense to collect specimens from the outer edges which have actively growing organisms; the center is mostly just dead skin and cellular debris. For more diffuse lesions, specimens need to be sampled from more areas.
Wear gloves at all times, avoid touching anything else
Clean the site with alcohol (70% isopropyl alcohol) or with non-medicated, non-fungicidal soap. This helps remove any contamination from saprophytic fingu and bacteria that would overgrow the culture of the suspected pathogen. Allow the lesion to dry prior to collecting the sample.
Pluck a sample of hair from the margin of the lesion using hemostats. Obtain samples from various parts of the lesion; the scale, crust and hair.
For circular, localized lesions, use sterile hemostats or thumb forceps to pluck several hairs from the edge of the lesion, esp broken, frayed, and distorted hairs. (Do not cut hairs for sampling, the actively growing areas are around the root. By cutting the hairs, you may not be able to obtain a suitable sample for dx.
For diffuse legions, pluck as many suspected hairs as you can, but also collect a sample with a sterile toothbrush or swab. Gently rub the surface of the lesion to collect hair and skin scales. |
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Term
| What simple in-house test would you perform in addition to a Wood’s lamp? |
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Definition
Direct Microscopic Examination
The parasitic form of dermatophytes in animal tissues appears as slender, greenish filaments in skin scrapings or so-called
arthroconidia inside or around the hair, creating a sheet of spores [28,29].
In order to visualize those structures it is necessary to clear the sample using a strong alkali solution such as KOH, NaOH or
Ca(OH)2; 10% KOH is the most common solution used by mycologists and clinicians |
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Term
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Definition
| Viruses consist of a nucleic acid (either DNA or RNA) associated with proteins encoded by the nucleic acid. The virus may also have a lipid bilayer (or envelope) but this is acquired from the host cell, usually by budding through a host cell membrane. If a membrane is present, it must contain one or more viral proteins to act as ligands for receptors on the host cell |
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Term
| 1. What is the size range of viruses? |
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Definition
| they range in size from about 20 to 400 nanometres in diameter (1 nanometre = 10-9 meters). |
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Term
| 1. List the techniques used to diagnose viral infections. |
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Definition
Many dzs may be dx on clinical and pathologic grounds. Serologic tests available for most viral dzs. These usually require paired serum samples collected 2 – 3 wks apart, early in the dz and on recovery. A rising antibody titer indicates recent infxn by the virus. Collection of serum samples from contact animals is worth considering because these animals are more likely to have low initial titers to the virus.
Virus isolation is expensive and time-consuming and may only provide a dx after the animals have recovered or died. However, in some cases, isolation and ID should be attempted, such as to establish the identity of a viral dz not previously seen in a practice, discover the exact agent when serologic and other tests have given equivolcal results, find the immunologic type of a virus in an epizootic, and verify the etiologic agent if a public health problem is involved. |
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Term
Describe submission to the external
diagnostic laboratory. |
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Definition
Submission of samples:
Should be refrigerated (4 Cel) when possible because virus titers decrease as temps rise. If they are to be delivered to the lab w/in 24 hours, they may be stored at 4 Cel and packed with coolant packs or ice in polystyrene-insulated carton for shipping. If the time delay will be longer than 24 h, snap freezing at -70 C and shipping on dry ice is desirable, except for specimens of suspected parainfluenza and influenza virus, in which case the integrity of these viruses is best preserved at – 20 C.
Must be shipped in airtight containers to prevent entry of carbon dioxide into the container. Carbon dioxide gas from the dry ice can lower the pH of fluid, killing any pH-labile viruses
Sm opcs of tissue, fecal material, or mucus can be preserved in vials filled with 50% glycol and stored at 4 C. a virus transport medium is available commercially.
Fecal materials and fluids often are submitted electron microscope exam. A fixative, such as universal or 10% buffered neutral formalin, should be added to the sample at a max of 1:1 fixative to sample to prevent overdilution of virus particles
Urine samples – approx 5 ml in sterile container. Virus transport medium should not be used. Must be kept chilled if to arrive in lab w/in 24 hrs of collection; otherwise it should be frozen at -27 C and shipped frozen.
If blood samples have been collected for serologic exam, they should be left at room temp and the clot allowed to retract . then they are refrigerated. Should not be frozen because freezing causes hemolysis and may make sample useless for serologic exam. |
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Term
| Describe the collection of specimens for viral testins |
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Definition
Viruses are often present in the nasel or pharyngeal secretions early in the acute stage of resp dzs. Mucosal scrapings rather than swabs of the secretions should be taken. Sterile wooden tongue depressors are useful for mucosal scrapings. Attempted isolation from blood samples may be considered in generalized catarrhal dzs that tend to have a viremic stage. Pox viruses often may be demonstrated by electron microscopy in fluid from early vesicular lesions and sometimes in scabs from early lesions.
Specimens should also be slected for indirect studies, such as serologic, hemotologic, histologic, and bacteriologic examinations. Viral dzs often are complicated by pathogenic bacteria acting as secondary invaders, which often can turn a mild viral infxn into a serious dz.
Specimens for histologic exam should consist of thin sections of tissue placed immediately in 10% formalin. Sections must never be frozen because this causes tissue artifacts that may be difficult to differentiate from a pathologic process.
Tissue samples for attempted virus isolation should be 2” cubes that contain both dzd and normal tissue if possible. Mucosal scrapings shouls be obtained instead of swabs. Sterile screw-capped containers should be used for collection, with a separate container for each sample. |
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Term
| 5. Describe paired serum samples |
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Definition
| collected 2 – 3 wks apart, early in the dz and on recovery |
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