NAVLE (North American Veterinary Licensing Examination) · USA / Canada · International Council for Veterinary Assessment (ICVA); scored by NBME, delivered by Prometric
Original practice questions written to the published syllabus · not past papersThe bacteria and fungi that cause disease in animals, genus by genus: what they are, where they live, what they cause and how they are identified.
In the exams: ICAR AICE-JRF core group 06; ICAR AIEEA-PG 13 (Microbiology); China preventive paper
NAVLE, BCSE, RCVS SME, AVE, SAVC and Asian licensing exams (China, Korea, Philippines, Nepal)
Clinical vignettes by species: sudden death with unclotted blood, crepitant swelling in a young steer, circling ewe fed silage, strangles outbreak, milk drop in a dairy herd, ringworm in a cat household, aspergillosis in birds, swollen vulvae in gilts; choice of sample, first-line test, public-health action and control.
How our questions for NAVLE spread across the units of Systematic Veterinary Bacteriology & Mycology. Difficulty: 1 easy, 20 medium, 15 hard.
| Aspergillus and Candida | 4 | |
| Clostridium | 3 | |
| Mycobacterium: tuberculosis and Johne's disease | 3 | |
| Pasteurella and Mannheimia | 3 | |
| Dermatophytes | 3 | |
| Staphylococcus | 2 | |
| Streptococcus | 2 | |
| Brucella | 2 | |
| Salmonella | 2 | |
| Escherichia coli | 2 | |
| Leptospira | 2 | |
| Listeria | 2 | |
| Mycoplasma | 2 | |
| Rickettsia and Chlamydia | 2 | |
| Bacillus anthracis | 1 | |
| Burkholderia mallei (glanders) | 1 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
A dog with recurrent pyoderma yields a coagulase-positive staphylococcus resistant to oxacillin and to several other drug classes. What does this most likely represent?
B. Methicillin-resistant Staphylococcus pseudintermedius carrying mecA
S. pseudintermedius is the main pyoderma pathogen of dogs, and oxacillin resistance marks methicillin resistance (mecA), often with multidrug resistance. S. epidermidis is coagulase negative, so it cannot fit a coagulase-positive result, and oxacillin resistance rules out a methicillin-sensitive strain.
Further reading: Quinn et al., Veterinary Microbiology and Microbial Disease; WOAH Terrestrial Manual
Several horses on a yard develop fever, nasal discharge and swollen, abscessing submandibular lymph nodes. After the outbreak, which animals are most important in keeping the infection on the yard?
C. Recovered horses carrying the organism in the guttural pouches
This is strangles, caused by Streptococcus equi subsp. equi. A proportion of recovered horses carry the organism in the guttural pouches, often with chondroids, and shed intermittently. Control uses endoscopy and PCR of guttural pouch lavage to find them. Drainage of lymph nodes does not clear guttural pouch carriage, and dogs and cats are not recognised reservoirs.
Further reading: Quinn et al., Veterinary Microbiology and Microbial Disease; WOAH Terrestrial Manual
A ram breeding soundness examination finds a firm, enlarged tail of the epididymis on one side. Which Brucella species should be investigated?
C. Brucella ovis
B. ovis causes epididymitis, usually in the tail of the epididymis, and reduced fertility in rams. It needs rough-antigen serology such as a specific ELISA or CFT. B. suis infects pigs and B. canis dogs.
Further reading: Quinn et al., Veterinary Microbiology and Microbial Disease; WOAH Terrestrial Manual
Cattle on a farm that is open to the public carry Shiga toxin-producing E. coli O157:H7. What is the significance for the cattle and for visitors?
B. Cattle are usually healthy carriers; visitors risk haemorrhagic colitis and HUS
Cattle carry E. coli O157:H7 in the gut without illness, while in people it can cause haemorrhagic colitis and haemolytic uraemic syndrome, especially in children. Hand washing after contact, separating eating areas and avoiding raw milk are the key controls. Oedema disease is a pig disease caused by a different Shiga toxin.
Further reading: Quinn et al., Veterinary Microbiology and Microbial Disease; WOAH Terrestrial Manual
Why is listeriosis in ruminants associated with poorly made silage?
D. Listeria multiplies in silage whose pH stays above about 5.5
Good fermentation drops silage pH to around 4 to 4.5, which suppresses Listeria; poorly fermented, aerobically spoiled or soil-contaminated silage stays above about pH 5.5 and allows multiplication. The signs come from infection, confirmed by microabscesses in the brainstem, not from mould toxins.
Further reading: Quinn et al., Veterinary Microbiology and Microbial Disease; WOAH Terrestrial Manual
A dairy herd that bought in heifers now has clinical mastitis that does not respond to intramammary penicillin, together with calf pneumonia and arthritis. Which screening test would be most useful for the herd?
A. PCR for Mycoplasma bovis on bulk tank milk
Mastitis that fails to respond to beta-lactams, plus calf pneumonia and arthritis after purchasing cattle, points to M. bovis, which lacks a cell wall. Bulk-milk PCR screens the herd. The CAMP test identifies S. agalactiae isolates, the milk ring test screens for Brucella, and bulk milk ZN staining is not a useful Johne's test.
Further reading: Quinn et al., Veterinary Microbiology and Microbial Disease; WOAH Terrestrial Manual
Many ewes in a flock abort in the last two to three weeks of pregnancy. The placentas have necrotic cotyledons and reddish-brown, thickened intercotyledonary areas, and smears stained with modified Ziehl-Neelsen show many small red elementary bodies. The most likely cause is:
A. Chlamydia abortus
Enzootic abortion of ewes, due to C. abortus, causes late abortion and a thickened placenta with reddish-brown exudate, and elementary bodies stain red with modified ZN. Campylobacter and Listeria are not modified-ZN positive. Toxoplasma produces small white foci on cotyledons with relatively normal intercotyledonary areas.
Further reading: Quinn et al., Veterinary Microbiology and Microbial Disease; WOAH Terrestrial Manual
Housed calves in winter develop grey, crusty, circular lesions around the eyes and on the head and neck, and a stockman develops an itchy ring on the forearm. The most likely organism is:
C. Trichophyton verrucosum
T. verrucosum is the main cattle ringworm fungus, with grey crusts around the eyes and head, and it infects people handling cattle. Dermatophilus causes paintbrush lesions in wet weather and is a bacterium; S. hyicus causes greasy pig disease.
Further reading: Quinn et al., Veterinary Microbiology and Microbial Disease; WOAH Terrestrial Manual
Growing pigs fed mouldy maize develop poor growth, jaundice and bleeding, and dairy cows on the same farm have a toxin in their milk. Which mycotoxin is involved?
D. Aflatoxin, appearing in milk as aflatoxin M1
Aflatoxins from Aspergillus flavus and A. parasiticus are hepatotoxic, causing jaundice, poor growth and coagulopathy, and aflatoxin B1 is converted to M1, which is excreted in milk and is regulated by milk limits. Zearalenone is oestrogenic, deoxynivalenol causes feed refusal and vomiting, and ergot causes gangrene of the extremities; none of these is the classic cause of liver damage with a milk residue.
Further reading: Quinn et al., Veterinary Microbiology and Microbial Disease; WOAH Terrestrial Manual
A cat has chronic nasal discharge and a firm swelling over the bridge of the nose. Nasal discharge mixed with India ink shows budding yeasts surrounded by wide clear haloes. The organism is most likely:
B. Cryptococcus
The clear halo in India ink is the thick polysaccharide capsule of Cryptococcus neoformans or C. gattii, the classic cause of nasal and nervous disease in cats; capsular antigen latex agglutination confirms it. Candida and Malassezia lack such a capsule, and Aspergillus forms hyphae, not yeasts.
Further reading: Quinn et al., Veterinary Microbiology and Microbial Disease; WOAH Terrestrial Manual
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