Test 1 - Epidemiology (11)

Question 1

Case Fatality Rate

Answer 1

The % of deaths among the clinically ill animals

Question 2

Mortality Rate

Answer 2

The number [%] of animals in a population that die from a particular disease over a specified period of time.

Question 3

Morbidity rate

Answer 3

The percentage of animals in a population that develop clinical signs attributable to a particular virus over a defined period of time (commonly the duration of an outbreak)

Question 4

Incidence

Answer 4

The number of new cases that occur in a population over a specified period of time

Question 5

Prevalence

Answer 5

The number of occurrences of disease (old and new), infection, or related attributes [antibodies] in a population, at a particular point of time.

It is difficult to measure the incidence of chronic diseases. For such diseases it is customary to determine the prevalence—that is, the ratio, at a particular point in time, of the number of cases currently present in the population divided by the number of animals in the population.

Question 6

Sporadic viral diseases

Answer 6

Viral diseases occurring occasionally, singly, or in scattered instances, and in a irregular and haphazard manner.

Question 7

Enzootic Viral diseases

Answer 7

The constant presence of a Viral disease within a given geographic area or population group.

Question 8

Epizootic viral disease

Answer 8

The occurrence of more cases of Viral diseases than expected in a given area or among a specific group of people/animals over a particular period of time. Refers to peaks in disease incidence that exceed the endemic/ enzootic baseline or expected incidence of disease.

Question 9

Panzootic viral diseases

Answer 9

Occurring over a very wide area (several countries or continents) and usually affecting a large proportion of the population

Question 10

What are the different types of carriers?

Answer 10

• Incubatory [acute] carriers: Animals that shed virus during the incubation period of the disease.
• Convalescent [chronic carriers]: animals that shed virus during recovery from disease.
• Inapparent carriers: Carrier state may exist in an animal with an infection that is inapparent throughout its course.

Question 11

Horizontal (lateral) transmission

Answer 11

Defined as the spread of an infectious agent from one person/animal or group to another person/animal or group.

Question 12

What are the different types of Horizontal transmission?

Answer 12

• Direct/Indirect Contact Transmission
• Vector transmission (mechanical/biological)
• Vehicle-born transmission
• Iatrogenic
• Nosocomial

Question 13

Droplet Transmission

Answer 13

Transmission of virus in droplet nuclei (saliva or mucus) that travel less than 1 meter from the source to the susceptible host.

It is a type of direct transmission.

Question 14

Airborne transmission

Answer 14

Spread of infectious agents by droplet nuclei in dust that travel more than one meter, sometimes for miles, from the infected to the susceptible host.

Droplets are small enough to remain in air for prolonged periods. Less than 5 micrometers in diameter

This is a type of indirect transmission

Question 15

The survival of the virus from one ‘vector season’ to the next (period during which arthropods hibernate) is called _______.

What are the important mechanisms?

Answer 15

“Overwintering”

• Transovarial transmission: The virus is transmitted from the mother tick through infected eggs to next generation of ticks.
• Trans-stadial transmission: The virus is transmitted from larva or nymph to next stage of development (nymph or adult). But not transmitted vertically (from mother tick to eggs and next generation).

Question 16

Arboviruses

Answer 16

A class of viruses transmitted to humans by arthropods such as mosquitoes and ticks. The first two letters of the words arthropod’ andborne, make up the ‘arbo’ that now designates this group of viruses as arthropod-borne.

Arboviruses are maintained in complex life cycles involving nonhuman primate/ vertebrate hosts and primary arthropod vectors.

Question 17

What are the different transmission cycles of Arboviruses?

Answer 17

• Enzootic cycle (Sylvatic or Jungle cycle): The natural transmission of virus between wild animals/birds (vertebrate hosts) and primary insect vectors.
• Epizootic cycle (rural cycle): The virus is transmitted between non-wild or domestic animals and the primary or accessory insect vectors.
• Urban cycle: The virus cycles between humans and insect vectors

Question 18

Amplifying Host

Answer 18

is in which the level of virus can become high enough that an insect vector such as a mosquito that feeds on it will probably become infectious.

Question 19

Dead-end or incidental host

Answer 19

host from which infectious agents are not transmitted to other susceptible hosts. They do not develop sufficient viremia to be picked up by the insect vectors.

Question 20

Bridge vector

Answer 20

is an arthropod that acquires virus from an infected wild animal and subsequently transmits the agent to human or secondary host.

Question 21

Common-vehicle Transmission

Answer 21

includes fecal contamination of food and water supplies (fecal–oral transmission) and virus-contaminated meat or bone products [e.g., for the transmission of vesicular exanthema of swine, classical swine fever (hog cholera) and bovine spongiform encephalopathy].

Question 22

Iatrogenic transmission

Answer 22

Infection that is transferred during medical or surgical practice.

This can happen in two ways:

• Introduction of pathogens by contaminated instruments (non-sterile surgical instruments, syringes), or contaminated body surface (inadequate handwashing). Example: Spread of equine infectious anemia virus via multiple-use syringes and needles.
• Introduction of pathogen through contaminated prophylactic or therapeutic preparations. Example: Presence of porcine circovirus genome in Rotavirus vaccine.

Question 23

Nosocomial transmission

Answer 23

occurs while an animal is in a veterinary hospital or clinic. Also known as Hospital Acquired Infection.

Example: During the peak of the canine parvovirus epidemic in the 1980s, many puppies became infected in veterinary hospitals and clinics.

Question 24

What are some things caused by vertical transmisison?

Answer 24

• Early embryonic death or abortion (e.g., several lentiviruses)
• Or may be associated with congenital disease (e.g., bovine viral diarrhea virus, border disease virus, porcine entero-virus),
• Or the infection may be the cause of congenital defects (e.g., Akabane virus, bluetongue virus, feline parvovirus).

Question 25

What are some of the mechanisms of survival of a virus?

Answer 25

• The physical stability of a virus affects its survival in the environment:
  Example: Viruses that are transmitted by the respiratory route have low environmental stability, whereas those transmitted by the fecal–oral route have a higher stability.
• Population Size is crucial: A virus may disappear from a population if supply of susceptible hosts is exhausted. This depends on size of population, immunity and pattern of virus shedding.
• Host Range: Many viruses can infect more than one host. Example, Foot and Mouth Disease Virus and Rotavirus.
• Persistent Infections: Virus remains in host for long periods
• Avoid exposure to external environment: Vertical Transmission, Venereal Transmission, Vector Transmission

Question 26

Herd Immunity

Answer 26

is a form of immunity that occurs when the vaccination of a significant portion of a population (or herd) provides a measure of protection for individuals who have not developed immunity.

Question 27

Describe the course of a typical infectious disease.

Answer 27

• Incubation period: refers to the interval between infection and the onset of clinical signs. In many diseases there is a period during which animals are infectious before they become sick.
• Prodromal period: The first signs and feelings of illness after incubation period. The period of early symptoms of a disease occurring after the incubation period and just before the appearance of the characteristic symptoms of the disease.
• Acute period: When the disease is at its height. Severe clinical signs.
• Decline period: Period when clinical signs begin to subside.
• Convalescent period: The body gradually returns to its pre-diseased state, and health is restored.