ASRB NET and ARS / SMS / STO (Agricultural Scientists Recruitment Board) · India · Agricultural Scientists Recruitment Board
Original practice questions written to the published syllabus · not past papersThe diseases of commercial and backyard poultry: viral, bacterial, parasitic, nutritional and toxic.
In the exams: ICAR AICE-JRF Medicine and Pathology units; China comprehensive paper poultry 20; SAVC poultry 15
How our questions for ASRB NET and ARS / SMS / STO spread across the units of Avian Pathology. Difficulty: 1 easy, 21 medium, 20 hard.
| Newcastle disease | 5 | |
| Avian influenza | 4 | |
| Infectious bursal disease | 4 | |
| Marek's disease | 4 | |
| Coccidiosis | 4 | |
| Infectious bronchitis | 3 | |
| Avian leucosis | 3 | |
| Mycoplasmosis | 3 | |
| Pullorum disease and fowl typhoid | 3 | |
| Mycotoxicosis | 3 | |
| Infectious laryngotracheitis | 2 | |
| Hydropericardium syndrome | 2 | |
| Necrotic enteritis | 2 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
Under the WOAH case definition, an APMV-1 isolate is regarded as causing Newcastle disease if its intracerebral pathogenicity index (ICPI) in day-old chicks is at least:
D. 0.7
WOAH defines Newcastle disease as infection with APMV-1 having an ICPI of 0.7 or more, or the multiple-basic-amino-acid motif at the F cleavage site. 1.2 is the IVPI threshold used for highly pathogenic avian influenza, the usual confusion; 2.0 is the maximum possible ICPI.
Further reading: Swayne (ed.), Diseases of Poultry, 14th ed.; WOAH Terrestrial Manual, Newcastle disease chapter
Mean death time (MDT) of chick embryos for an APMV-1 isolate is 52 hours. How is the isolate classified?
A. Velogenic
MDT under 60 hours indicates velogenic strains, 60-90 hours mesogenic, and over 90 hours lentogenic. Students often reverse the scale, thinking a short time means a mild virus; in fact the faster the embryos die, the more virulent the virus.
Further reading: Swayne (ed.), Diseases of Poultry, 14th ed.; WOAH Terrestrial Manual, Newcastle disease chapter
Which viral protein carries the main virus-neutralising epitopes and determines the serotype of infectious bronchitis virus?
A. S1 subunit of the spike glycoprotein
S1 carries the neutralising and HI epitopes and differs between serotypes, so S1 sequencing is used for genotyping. The nucleocapsid protein is conserved and underlies group-specific ELISA; S2 is the more conserved stalk that anchors the spike.
Further reading: Swayne (ed.), Diseases of Poultry, 14th ed.; Pattison et al., Poultry Diseases, 6th ed.
Broilers aged 25 days show increased water intake, wet litter and rising mortality. The kidneys are swollen and pale with tubules and ureters distended by urates; the trachea shows mild mucus. Feed calcium and water supply are normal. Which approach best confirms the cause and guides control?
D. RT-PCR of kidney and trachea for infectious bronchitis virus, with S1 sequencing compared with vaccine strains
Nephropathogenic IBV strains cause exactly this picture; RT-PCR plus S1 sequencing identifies the genotype and whether current vaccines match it. Ochratoxin is a reasonable differential, but IB certainly can affect kidneys, so testing only for ochratoxin would miss the likely cause; pullorum and nerve histology do not fit.
Further reading: Swayne (ed.), Diseases of Poultry, 14th ed.; Pattison et al., Poultry Diseases, 6th ed.
A previously healthy layer flock develops infectious laryngotracheitis two weeks after the birds were moved to a new laying house at 18 weeks. The farm had an outbreak three years earlier and the birds were vaccinated as chicks. What is the most likely source?
A. Reactivation of latent virus in carrier birds under the stress of moving and onset of lay
Vaccinated and recovered birds can carry latent ILT virus in the trigeminal ganglion and shed it again when stressed, for example at transfer and onset of lay. ILT virus is not transmitted vertically, and feed and wild ducks are not recognised routes.
Further reading: Swayne (ed.), Diseases of Poultry, 14th ed.; Pattison et al., Poultry Diseases, 6th ed.
Day-old broiler chicks have a mean IBD ELISA titre of 4000. The chosen intermediate vaccine can break through a titre of 500, and the maternal antibody half-life is taken as 3 days. Using the Deventer formula, and ignoring any correction for the time the vaccine takes to reach the bursa, at what age should the flock be vaccinated?
B. Day 10
Age = (log2 4000 - log2 500) x half-life + age at sampling = log2(8) x 3 + 1 = 3 x 3 + 1 = day 10. Day 9 omits the age at sampling; day 18 uses the layer half-life (about 5.5 days) instead of the broiler value (3 x 5.5 + 1 = 17.5); day 7 uses a half-life of 2 days.
Further reading: Swayne (ed.), Diseases of Poultry, 14th ed.; Pattison et al., Poultry Diseases, 6th ed.
From which tissue is fully infectious, cell-free Marek's disease virus released into the environment?
B. Feather follicle epithelium
In most tissues MDV is cell-associated, but the feather follicle epithelium produces enveloped infectious virus shed in dander, which remains infectious in dust for months. The trigeminal ganglion is the latency site of ILT virus, and the oviduct is a site of vertical transmission for other agents.
Further reading: Swayne (ed.), Diseases of Poultry, 14th ed.; Pattison et al., Poultry Diseases, 6th ed.
Which statement best explains why Marek's disease virus field strains have increased in virulence over several decades?
A. Vaccines prevent tumours but not infection or shedding, letting more virulent strains transmit from vaccinated birds
MD vaccines are 'leaky': vaccinated birds stay infected and shed virus, so strains that would kill unvaccinated hosts quickly can still transmit, favouring increasing virulence (vMDV to vvMDV to vv+MDV). Loss of Meq would reduce oncogenicity; MDV is not vertically transmitted; herpesviruses have non-segmented DNA genomes and do not reassort.
Further reading: Swayne (ed.), Diseases of Poultry, 14th ed.; Pattison et al., Poultry Diseases, 6th ed.
A broiler farm uses salinomycin in feed. The vet plans to treat a mycoplasma outbreak through the water. Which drug should be avoided because of a toxic interaction with the ionophore?
C. Tiamulin
Tiamulin inhibits the metabolism of monensin, narasin and salinomycin, causing ionophore toxicity with muscle weakness and death. Tylosin, doxycycline and lincomycin do not have this classic interaction. Any drug choice and dose must be confirmed against the product label and national formulary.
Further reading: Swayne (ed.), Diseases of Poultry, 14th ed.; Pattison et al., Poultry Diseases, 6th ed.
Two-week-old chicks from one hatchery gasp and die. Post-mortem shows multiple yellow-white caseous nodules in the lungs and air sacs, and a wet mount shows septate branching hyphae. How does this differ from mycotoxicosis?
C. It is aspergillosis: infection by inhaled Aspergillus fumigatus spores, not poisoning by a fungal metabolite in feed
Aspergillosis (brooder pneumonia) is infection with fungal growth in lesions, usually from contaminated hatchers or litter; mycotoxicosis is poisoning by toxins in feed with no fungus in the tissues. Aflatoxin, ochratoxin and T-2 do not produce fungal nodules in the lungs.
Further reading: Swayne (ed.), Diseases of Poultry, 14th ed., mycotoxicoses chapter; Pattison et al., Poultry Diseases, 6th ed.
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