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 bacterial and related infectious diseases of livestock and horses: clinical signs, diagnosis, treatment, prevention and control.
In the exams: ICAR AICE-JRF core group 07 (Medicine); ICAR AIEEA-PG 13; China infectious diseases 30; TNPSC Micro/VPH/Preventive Medicine 30
NAVLE, BCSE, RCVS SME, AVE, SAVC
Clinical vignettes: coliform versus contagious mastitis, strangles outbreak management and purpura, tetanus in a horse, leptospirosis in a dog, SICCT interpretation, Johne's control, ringworm in a cattery, and when to notify the state veterinarian.
How our questions for NAVLE spread across the units of Preventive Veterinary Medicine I: Bacterial, Fungal, Rickettsial and Mycoplasmal Diseases. Difficulty: 5 easy, 20 medium, 11 hard.
| Mastitis | 8 | |
| Strangles | 6 | |
| Clostridial diseases: black quarter, enterotoxaemia and tetanus | 4 | |
| Leptospirosis | 4 | |
| Ringworm | 4 | |
| Listeriosis | 2 | |
| Johne's disease | 2 | |
| Caseous lymphadenitis | 1 | |
| Brucellosis | 1 | |
| Glanders | 1 | |
| Actinomycosis and actinobacillosis | 1 | |
| Anaplasmosis | 1 | |
| Anthrax | 1 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
A 50-cow herd: 40 cows give 20 kg/day at 150,000 cells/mL, 8 cows give 15 kg/day at 900,000 cells/mL, and 2 cows give 10 kg/day at 3,000,000 cells/mL. What is the expected bulk-tank SCC?
D. About 306,000 cells/mL
Bulk SCC is weighted by milk yield: (800 kg x 150,000 + 120 kg x 900,000 + 20 kg x 3,000,000) / 940 kg = 288,000,000 / 940 = 306,383 cells/mL (kg of milk is treated as litres, which is close enough for this estimate). The unweighted cow average (384,000) ignores that high-SCC cows give less milk; 1,350,000 is the mean of the three group values; 248,000 is the result after the two worst cows are removed.
Where do most long-term carriers of Streptococcus equi harbour the organism?
C. Guttural pouches, sometimes as chondroids
Persistent guttural pouch empyema and chondroids (concretions of inspissated pus) harbour S. equi for months or years; endoscopy with lavage for culture and PCR detects them. Renal carriage is a feature of leptospirosis, not strangles.
A yard of 30 horses has a confirmed strangles case. Which step best identifies horses that could restart the outbreak after clinical recovery?
A. Guttural pouch lavage PCR and culture
Carriers shed intermittently from the guttural pouches, so a single nasal swab often misses them; guttural pouch lavage with PCR and culture is the most sensitive method. Blanket penicillin does not clear guttural pouch chondroids, and vaccinating exposed horses can risk purpura. Both recovered and in-contact horses should be sampled.
Which species is most sensitive to tetanus toxin?
B. Horse
Horses (and humans) are highly sensitive; dogs and cats are relatively resistant and often show localised tetanus, and birds are highly resistant.
An unvaccinated horse has a deep puncture wound of the hoof. The recommended tetanus prophylaxis is:
A. Tetanus antitoxin plus a first toxoid dose at a separate site, then completing the course
Toxoid takes weeks to induce immunity, so an unvaccinated horse needs antitoxin for immediate passive protection, with toxoid at a separate site to begin active immunity. Penicillin kills the organism but does not neutralise toxin already formed.
Eight weeks after receiving equine-origin tetanus antitoxin, a horse develops jaundice, hepatic encephalopathy and very high liver enzymes. What is the likely condition?
A. Serum hepatitis (Theiler's disease)
Theiler's disease, now associated with equine parvovirus-hepatitis, is acute hepatic necrosis following administration of equine-origin biologics such as tetanus antitoxin. Pyrrolizidine toxicity comes from plants, not antitoxin.
The most important infectious cause of equine recurrent uveitis is:
D. Leptospira
Leptospiral infection, often serovar Pomona in North America, is the most strongly associated cause of equine recurrent uveitis ('moon blindness'). Onchocerca has been implicated historically but is not the main cause.
A five-year-old cow has had persistent diarrhoea and weight loss for two months, with normal appetite, no fever and submandibular oedema. The most likely diagnosis is:
B. Johne's disease
Chronic diarrhoea without fever and with good appetite, progressive weight loss and bottle jaw in an adult cow are classic for clinical Johne's disease. Salmonellosis is usually febrile and acute; winter dysentery is an acute herd outbreak.
A kitten's scaly facial lesions do not fluoresce under a Wood's lamp. What is the correct conclusion?
B. Dermatophytosis is not ruled out, as not every M. canis infection fluoresces
Not every M. canis infection fluoresces apple-green (older texts say about half of strains; careful studies find most infected cats do), and other dermatophytes do not, so a negative Wood's lamp does not exclude ringworm; trichogram, culture or PCR follow. A negative result is not evidence of Trichophyton.
A horse with suspected tetanus shows which sign when its head is raised or its face tapped?
B. Third-eyelid prolapse
Retraction of the eyeball by spastic muscles pushes the third eyelid across the eye, a classic early sign. Head tilt and nystagmus suggest vestibular disease.
Ten here, 36 in the app. The Laisha app has every practice question we have written to NAVLE in this subject, marked as you go, with timed papers, a jump-to-unanswered list and a certificate when you pass at 70 per cent.
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