National Licensure Examination for Veterinarians (NLEV) · Nepal · Nepal Veterinary Council (NVC Act 2055 BS)
Original practice questions written to the published syllabus · not past papersWater and air hygiene, waste and carcass disposal, disinfection, pollution and climate change as they affect animal and human health.
In the exams: NAVLE environmental health and safety 5%
How our questions for National Licensure Examination for Veterinarians spread across the units of Environment & Environmental Hygiene. Difficulty: 19 easy, 26 medium, 5 hard.
| Water hygiene | 10 | |
| Waste management on livestock farms | 9 | |
| Disinfection | 8 | |
| Air hygiene | 6 | |
| Environmental pollution | 6 | |
| Biomedical waste | 5 | |
| Climate change and livestock | 4 | |
| Carcass disposal | 1 | |
| Experimental animal medicine | 1 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
The result of the multiple-tube fermentation test for coliforms is expressed as:
C. Most probable number per 100 mL
Tube results are converted with statistical tables to a most probable number per 100 mL. Colony counts per 100 mL come from membrane filtration, not from tubes; plaque counts are for phages and viruses.
Further reading: APHA Standard Methods for the Examination of Water and Wastewater
In membrane filtration testing of water, the pore size of the filter normally used to retain coliform bacteria is:
C. 0.45 µm
A 0.45 µm membrane retains coliforms while allowing water through at a practical rate; colonies on the filter are counted directly per 100 mL. 4.5 µm and 45 µm would let bacteria pass; 0.02 µm is an ultrafiltration size that would clog quickly.
Further reading: APHA Standard Methods
Why is chlorination more effective in water at pH 6.5 than at pH 8.5?
D. More of the free chlorine is present as hypochlorous acid
Free chlorine exists as hypochlorous acid (HOCl) and hypochlorite ion (OCl−); HOCl dominates at lower pH and is the far more effective biocide because it is uncharged and penetrates cells. Hypochlorite ion is the weaker form that dominates at high pH. Chloramines are slower, weaker disinfectants.
Further reading: WHO Guidelines for Drinking-water Quality; McDonnell, Antisepsis, Disinfection and Sterilization
In a BOD test, 6 mL of dairy effluent is diluted to 300 mL. Dissolved oxygen is 8.6 mg/L at the start and 3.4 mg/L after 5 days at 20 °C. What is the BOD5 of the effluent?
C. 260 mg/L
BOD = (DO initial − DO final) / P, where P = 6/300 = 0.02. BOD = (8.6 − 3.4) / 0.02 = 5.2 / 0.02 = 260 mg/L. 5.2 forgets the dilution; 255 uses 6/294 (sample to diluent) instead of sample to total volume; 52 uses a factor of 10.
Further reading: APHA Standard Methods
For efficient aerobic composting of manure, the starting carbon to nitrogen ratio should be about:
B. 25–30 : 1
A C:N of about 25–30:1 balances microbial energy (carbon) and protein (nitrogen) needs. Ratios as low as 5:1 lose nitrogen as ammonia; at 100:1 composting is slow because nitrogen limits microbial growth.
Further reading: On-farm composting handbooks (NRAES-54)
Biogas from anaerobic digestion of cattle dung consists mainly of:
B. Methane, about 50–70%, with most of the rest carbon dioxide
Biogas is typically 50–70% methane and 30–50% carbon dioxide, with traces of hydrogen sulphide and water vapour. Carbon monoxide is not a normal digestion product.
Further reading: FAO and national biogas manuals
Why should carcasses be moved as little as possible during an outbreak of a contagious disease?
C. Transport spreads the pathogen along the route and to other premises
Leaking fluids, flies and contaminated vehicles can spread infection along the route and at the destination; when carcasses must be moved, leak-proof covered vehicles and cleaned routes are used. Transport is restricted, not universally banned.
Further reading: WOAH Terrestrial Code, disposal of dead animals
Under India's Bio-Medical Waste Management Rules, 2016, used hypodermic needles from a veterinary hospital go into:
B. White translucent puncture-proof container
Sharps, including needles and blades, go into white translucent puncture-proof containers. Red bags take contaminated recyclable plastics such as tubing and syringes without needles; yellow takes anatomical and soiled waste; blue takes glassware and metal implants.
Further reading: Bio-Medical Waste Management Rules, 2016 (India)
Under India's Bio-Medical Waste Management Rules, 2016, placental tissue from a caesarean section in a cow goes into:
A. A yellow bag, for incineration or approved alternative
Anatomical waste, including tissues, organs and placentas, is yellow-category waste sent for incineration, plasma pyrolysis or permitted deep burial. Red is for recyclable contaminated plastics and blue for glass; anatomical waste is never general waste.
Further reading: Bio-Medical Waste Management Rules, 2016 (India)
Why is 70% ethanol a better disinfectant than absolute (100%) ethanol?
C. Water is needed for effective protein denaturation and penetration
Water assists protein denaturation and allows alcohol to penetrate cells; absolute alcohol dehydrates and coagulates surface proteins, which protects the organism. Neither strength kills bacterial spores.
Further reading: McDonnell, Antisepsis, Disinfection and Sterilization
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