ICAR AICE-JRF/SRF (PhD) · India · NTA for ICAR
Original practice questions written to the published syllabus · not past papersHow disease is measured, studied and controlled in populations, from incidence and prevalence to surveillance and outbreak investigation, plus the major zoonoses and One Health.
In the exams: Nepal NLEV Epidemiology & Public Health 6; SAVC epidemiology 15 and zoonoses 25; EGEL Plus epidemiology 15; ICAR AICE-JRF core group 06
How our questions for ICAR AICE-JRF/SRF spread across the units of Veterinary Epidemiology & Zoonoses. Difficulty: 7 easy, 32 medium, 20 hard.
| Epidemiological study designs | 8 | |
| Evaluation of diagnostic tests: sensitivity and specificity | 7 | |
| Zoonoses: leptospirosis, glanders, KFD, avian influenza and Japanese encephalitis | 7 | |
| Measures of disease frequency: incidence, prevalence, morbidity, mortality and case fatality | 6 | |
| Terms of disease occurrence: sporadic, enzootic, epizootic, panzootic and exotic | 5 | |
| Sampling for disease surveys | 5 | |
| Zoonoses: rabies, brucellosis, tuberculosis and anthrax | 5 | |
| Transboundary animal diseases and WOAH | 4 | |
| Surveillance | 3 | |
| Risk analysis | 3 | |
| Outbreak investigation | 3 | |
| One Health | 3 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
A disease that is present in a cattle population at a usual, fairly constant and predictable frequency is described as:
A. Enzootic
Enzootic (the animal equivalent of endemic) means present at the expected, stable level. Epizootic means clearly above the expected level; sporadic means irregular and unpredictable; exotic means not normally present in the country.
Further reading: Thrusfield M et al., Veterinary Epidemiology, 4th ed.
Given R0 = 4 for an infection in a homogeneously mixing, fully susceptible population, what proportion must be immune to prevent sustained spread?
A. 75%
Herd immunity threshold = 1 - 1/R0 = 1 - 1/4 = 0.75, or 75%. Answering 25% gives 1/R0 itself; 80% is the threshold for R0 = 5; 33% wrongly uses 1/(R0 - 1).
Further reading: Thrusfield M et al., Veterinary Epidemiology, 4th ed.
A new treatment for a chronic disease prolongs survival but does not cure it. If incidence does not change, what happens to prevalence?
D. It rises
Prevalence depends on incidence and duration. Prolonging survival without cure lengthens duration, so more animals are living with the disease at any time and prevalence rises, even though no additional animals are becoming diseased.
Further reading: Thrusfield M et al., Veterinary Epidemiology, 4th ed.
A case-control study of salmonellosis in herds gives: cases exposed 40, cases unexposed 60, controls exposed 20, controls unexposed 80. What is the odds ratio?
A. 2.67
OR = ad/bc = (40 x 80)/(20 x 60) = 3200/1200 = 2.67. 2.00 is 40/20, a ratio of exposed counts. 1.56 comes from treating the table as if risks could be computed, which a case-control design does not allow. 0.38 is the inverse.
Further reading: Thrusfield M et al., Veterinary Epidemiology, 4th ed.
In a study of mastitis, cows kept on straw yards had more mastitis, but these cows were also older on average, and age independently increases mastitis risk. Age here is best described as a:
A. Confounder
A confounder is associated with the exposure, is an independent cause of the outcome and is not on the causal pathway. Age meets all three. It can be controlled by stratification, matching or multivariable analysis. An effect modifier changes the size of the effect across strata, which is a different concept.
Further reading: Thrusfield M et al., Veterinary Epidemiology, 4th ed.
A test with sensitivity 95% and specificity 98% is used to screen a population in which true prevalence is 1%. What is the positive predictive value?
C. About 32%
PPV = P x Se/[P x Se + (1 - P)(1 - Sp)] = 0.0095/(0.0095 + 0.0198) = 0.324. At low prevalence false positives outnumber true positives, even with a good test. About 3% is the apparent prevalence (0.0095 + 0.0198 = 0.029), not PPV. 95% is the PPV the same test would reach at about 30% prevalence.
Further reading: Thrusfield M et al., Veterinary Epidemiology, 4th ed.
In a WOAH import risk assessment, the step that describes the biological pathways by which an imported commodity could carry a pathogen into the importing country is:
B. Entry assessment
Entry assessment (formerly release assessment) covers the pathway to the border. Exposure assessment covers how susceptible animals or people in the importing country could then be exposed.
Further reading: WOAH Terrestrial Animal Health Code
In Kyasanur Forest disease areas, what is the classic early warning of increased virus activity?
D. Deaths of langurs and bonnet macaques in the forest
Monkeys are highly susceptible and die of the infection, amplifying virus for ticks. The disease was discovered after monkey deaths, and monkey death reports trigger investigation and tick control.
Further reading: Thrusfield M et al., Veterinary Epidemiology, 4th ed.
Which serovar-maintenance host pairing for Leptospira is correct?
B. Hardjo in cattle
Typical pairings are Icterohaemorrhagiae in rats, Hardjo in cattle, Pomona and Bratislava in pigs and Canicola in dogs. The distractors swap the hosts.
Further reading: Thrusfield M et al., Veterinary Epidemiology, 4th ed.
According to the WOAH Manual criteria, an avian influenza isolate is classified as highly pathogenic if it:
D. Has an intravenous pathogenicity index above 1.2 in six-week-old chickens
HPAI is defined by an IVPI above 1.2 in six-week-old chickens, or at least 75% mortality in four- to eight-week-old chickens inoculated intravenously, or, for H5 and H7 viruses, a haemagglutinin cleavage site with multiple basic amino acids similar to known HPAI viruses. The N subtype does not define pathogenicity.
Further reading: WOAH Manual of Diagnostic Tests and Vaccines for Terrestrial Animals
Ten here, 59 in the app. The Laisha app has every practice question we have written to ICAR AICE-JRF/SRF 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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