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 papersVirus structure and replication, the virus families behind the major animal plagues and pet diseases, and how viral infections are diagnosed and vaccinated against.
In the exams: ICAR AICE-JRF core group 06; ICAR AIEEA-PG 13 (Microbiology); China infectious diseases 30
How our questions for ASRB NET and ARS / SMS / STO spread across the units of Systematic Veterinary Virology. Difficulty: 21 easy, 20 medium, 28 hard.
| Viral diagnostics | 10 | |
| Viral vaccine technology | 7 | |
| African and classical swine fever viruses | 6 | |
| Virus structure | 5 | |
| Virus replication | 5 | |
| Bluetongue virus | 5 | |
| Newcastle disease virus | 5 | |
| Infectious bursal disease virus | 5 | |
| Avian influenza virus | 4 | |
| Foot-and-mouth disease virus | 3 | |
| PPR virus and rinderpest (history of eradication) | 3 | |
| Capripoxviruses and lumpy skin disease virus | 3 | |
| Rabies virus | 3 | |
| Marek's disease virus | 3 | |
| Canine parvovirus and canine distemper virus | 1 | |
| Equine influenza and equine infectious anaemia viruses | 1 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
Which pair of viruses uses reverse transcriptase during replication?
D. Feline leukaemia virus and equine infectious anaemia virus
Both named viruses are retroviruses, a gammaretrovirus and a lentivirus, and both copy their RNA into DNA that integrates as a provirus, which is why infection is lifelong. The morbilliviruses in the third option are negative-sense RNA viruses, the first pair are large DNA viruses, and the second are double-stranded RNA viruses; none uses reverse transcription.
Further reading: Standard veterinary virology texts and WOAH Terrestrial Manual disease chapters
Lumpy skin disease virus is spread mainly by:
B. Mechanical transmission by biting flies, mosquitoes and ticks
Transmission is chiefly mechanical on the mouthparts of biting arthropods, which explains the seasonality and the jumps between distant herds; direct contact plays a smaller part and virus is also present in semen. Aerosol spread and feed-borne spread are not the main routes, and there is no established biological cycle in sandflies.
Further reading: Standard veterinary virology texts and WOAH Terrestrial Manual disease chapters
Virulence of Newcastle disease virus is determined chiefly by:
C. The amino acid sequence at the fusion protein precursor cleavage site
Virulent strains carry several basic amino acids at the F0 cleavage site with phenylalanine at position 117, so the precursor is cleaved by proteases present in many tissues; avirulent strains need trypsin-like enzymes restricted to the respiratory and intestinal tracts. Influenza-style HA subtypes do not exist in this virus.
Further reading: Standard veterinary virology texts and WOAH Terrestrial Manual disease chapters
Which serological test is routinely used to monitor flock immunity to Newcastle disease?
B. Haemagglutination inhibition
Haemagglutination inhibition measures antibody that blocks the virus from agglutinating red cells and is the standard flock monitoring test, read as a titre in doubling dilutions. The Coggins test is for equine infectious anaemia and is a common distractor drawn from a different species.
Further reading: Standard veterinary virology texts and WOAH Terrestrial Manual disease chapters
Which vaccine approach removes the problem of timing live infectious bursal disease vaccination around maternal antibody?
A. Turkey herpesvirus-vectored VP2 or immune-complex vaccine, given in ovo or at hatch
A vectored vaccine delivers the protective VP2 antigen inside a carrier virus that maternal antibody to the bursal disease virus does not neutralise, and immune-complex vaccines release antigen as antibody wanes; both can be applied in ovo or at hatch. Inactivated vaccine at hatch does not protect chicks in time, and doubling a live dose does not overcome neutralisation reliably.
Further reading: Standard veterinary virology texts and WOAH Terrestrial Manual disease chapters
A major obstacle to conventional inactivated vaccines against African swine fever is that:
B. Infection does not induce effective virus-neutralising antibody
Because neutralising antibody is not an effective correlate of protection for this virus, killed preparations have not protected pigs; live attenuated candidates with virulence genes deleted have been licensed in Vietnam, but safety and reversion concerns remain. The genotypes defined by sequencing the major capsid protein gene are not serotypes.
Further reading: Standard veterinary virology texts and WOAH Terrestrial Manual disease chapters
A single positive antibody titre in an unvaccinated animal tells you:
B. That the animal has been exposed at some time, not that it is infected now
Antibody persists long after recovery, so one titre marks exposure. Current infection is shown by a four-fold or greater rise between paired acute and convalescent sera taken two to four weeks apart, or by specific IgM, or by detecting the agent itself.
Further reading: Standard veterinary virology texts and WOAH Terrestrial Manual disease chapters
A competitive ELISA can be used on serum from any species because:
D. A labelled monoclonal competes with serum antibody, so no anti-species conjugate is needed
Because the label is on a reagent antibody, not on an anti-species conjugate, the same kit works on cattle, sheep, goats and wildlife, which is why the bluetongue VP7 and PPR competitive ELISAs are so widely used. Indirect ELISAs need a conjugate matched to the species.
Further reading: Standard veterinary virology texts and WOAH Terrestrial Manual disease chapters
DIVA testing depends on:
C. A vaccine lacking (or carrying) a marker antigen, paired with a test for antibody to it
The principle is a difference in antigenic content between vaccine and field virus, detected by a companion serological test: antibody to foot-and-mouth disease non-structural proteins, or to the classical swine fever Erns protein with an E2 subunit vaccine. Sensitivity of a genome test has nothing to do with it.
Further reading: Standard veterinary virology texts and WOAH Terrestrial Manual disease chapters
In a field trial, 240 of 800 unvaccinated animals and 36 of 1,200 vaccinated animals developed disease. What is the vaccine efficacy?
B. 90%
Attack rate unvaccinated = 240/800 = 0.30; attack rate vaccinated = 36/1,200 = 0.03. Efficacy = (0.30 - 0.03)/0.30 = 0.90, that is 90%. Answering 27% subtracts the attack rates without dividing by the unvaccinated rate, and 85% comes from comparing raw case numbers (1 - 36/240) while ignoring the different group sizes; 15% is that raw ratio itself.
Further reading: Standard veterinary virology texts and WOAH Terrestrial Manual disease chapters
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