Lecture 4, Zoonoses

Question 1

The word ‘zoonoses’ is derived from the Greek words…?

Answer 1

zōon meaning ‘animal’ and nosos means ‘disease’.

Question 2

The term ‘zoonoses’ was coined by

Answer 2

Rudolf Virchow during his study on Trichinella in 1855, to indicate the infectious disease link between animal and human health.

Question 3

As described by the World Health Organization (WHO), ‘A zoonosis is

Answer 3

any disease or infection that is naturally transmissible from vertebrate animals to humans’.

Question 4

The classic zoonoses which have been well known for centuries and are still causing major socio-economic effects in many parts of the globe. (9)

Answer 4

rabies, plague, leptospirosis, brucellosis, bovine tuberculosis, cysticercosis, echinococcosis, toxoplasmosis and yellow fever

Question 5

In recent years, new zoonotic entities are posing a serious threat to the globalized world. Name some examples. (min 8)

Answer 5

e.g. Lyme borreliosis, cryptosporidiosis, Ebola, Nipah, severe acute respiratory syndrome coronavirus (SARS-CoV), Middle East respiratory syndrome (MERS), influenza viruses of animal origin (swine flu – H1N1), hantavirus, etc.

Question 6

Name 2 zoonotic pathogens that have been used as biologic weapons.

Answer 6

e.g. anthrax and glanders

Question 7

Zoonoses can be classified in three ways:

Answer 7

Classification of zoonoses based on etiological agents.

Classification of zoonoses based on the reservoir host(s) (and the life cycle of the infecting pathogen).

Classification based on the transmission cycle.

Question 8

Zoonoses can be caused by a range of pathogens such as

Answer 8

viruses, bacteria, fungi and parasites.

In a study, out of the listed 1415 pathogens known to infect humans, 61% were found to be zoonotic.

Question 9

Zoonoses can be classified based on the reservoir host(s) and

Answer 9

the life cycle of the infecting pathogen.

Question 10

The reservoir of an infectious agent is

Answer 10

the habitat in which the agent normally lives, grows and multiplies.

Question 11

The reservoirs for zoonotic pathogens include

Answer 11

humans, animals and the environment.

Question 12

Based on reservoir hosts, zoonoses can be classified as follows: (3)

Answer 12

Anthropozoonoses
Zooanthroponoses
Amphixenoses

Question 13

Anthropozoonoses are

Answer 13

The zoonotic diseases which can be transmitted to humans from lower vertebrates.

Therefore, these infections primarily affect animals but can be naturally transmitted to humans (e.g. rabies, brucellosis, Q fever, leptospirosis, ringworm, etc.).

Question 14

Zooanthroponoses are

Answer 14

(also known as ‘reverse zoonotic disease transmission’):

Those zoonotic diseases which can be transmitted to lower vertebrate animals from infected humans.

Therefore, these infections are primarily of human origin (e.g. methicillin-resistant Staphylococcus aureus, Cryptosporidium parvum, Ascaris lumbricoides, etc.).

Question 15

Amphixenoses are

Answer 15

The zoonoses which are maintained in both humans and lower vertebrate animals, which may be transmitted in either direction (e.g. Staphylococcus infection, E. coli infection, salmonellosis, etc.).

Question 16

Direct zoonoses are

Answer 16

Those zoonotic diseases which are perpetuated in nature by a single vertebrate species (e.g. anthrax, rabies, Q fever, etc.).

Question 17

Cyclozoonoses are

Answer 17

Zoonotic diseases which require two or more vertebrate hosts to complete the transmission cycle.

Question 18

Cyclozoonoses can be further classified as follows:

Answer 18

Obligatory cyclozoonoses and
Non-obligatory cyclozoonoses

Question 19

Obligatory cyclozoonoses are

Answer 19

The zoonotic diseases in which the involvement of humans as a host is compulsory to continue the transmission cycle (e.g. taeniasis).

Question 20

Non-obligatory cyclozoonoses are

Answer 20

The zoonotic diseases in which humans are accidentally involved in the transmission cycle of the pathogen (e.g. hydatidosis).

Question 21

Metazoonoses are

Answer 21

The zoonotic diseases which require both vertebrate and invertebrate hosts to continue their transmission cycle.

Question 22

Saprozoonoses are

Answer 22

The zoonotic diseases which require an inanimate object(s) for the completion of the transmission cycle are known as saprozoonoses.

Saprozoonoses can be classified as:
Saproanthropozoonoses
Saproamphixenoses
Saprometanthropozoonoses

Question 23

Saproanthropozoonoses are

Answer 23

The zoonoses which can transfer from animals to humans through inanimate substances (e.g. erysipeloid).

Question 24

Saproamphixenoses are

Answer 24

The zoonoses which can be shared between humans and animals through inanimate objects (e.g. histoplasmosis).

Question 25

Saprometanthropozoonoses are

Answer 25

These zoonoses require vertebrate hosts and invertebrate hosts as well as inanimate objects for the completion of their life cycle (e.g. fascioliasis).

Question 26

Classification of Zoonoses According to the Ecosystem in which Pathogens Circulate

Answer 26

Synanthropic zoonoses &
Exoanthropic zoonoses

Question 27

Synanthropic zoonoses are

Answer 27

The zoonotic diseases which transmit through the urban (domestic) cycle where the sources of infection(s) are domestic and synanthropic animals (e.g. urban rabies, cat-scratch disease and zoonotic ringworm through pets).

Question 28

Exoanthropic zoonoses are

Answer 28

The zoonotic diseases which transmit through the sylvatic cycle in natural foci through feral or wild animals (e.g. arboviruses, wildlife rabies, Lyme disease and tularemia).

Note: Some zoonoses can circulate in both urban and sylvatic cycles (e.g. yellow fever and Chagas disease).

Question 29

Direct contact of a susceptible host with infected animals.

Give 3 examples of diseases that transmit in this way.

Answer 29

e.g. scabies, brucellosis, leptospirosis

Question 30

What is the sylvatic cycle?

Answer 30

also enzootic or sylvatic transmission cycle, is a portion of the natural transmission cycle of a pathogen. Sylvatic refers to the occurrence of a subject in or affecting wild animals.

The sylvatic cycle is the fraction of the pathogen population’s lifespan spent cycling between wild animals and vectors.

Question 31

Direct transmission through animal bites and scratches.

Give 2 examples of diseases that transmit in this way.

Answer 31

bites (e.g. rabies) and scratches (e.g. cat-scratch fever).

Question 32

Transmission through contaminated animal food products, mainly due to improper food handling and inadequate cooking practices.

Give 3 examples of pathogens that transmit in this way.

Answer 32

e.g. Salmonella spp., Clostridium perfringens, E. coli, etc.

Question 33

Feco–oral transmission from animals to humans.

Give 3 examples of pathogens that transmit in this way.

Answer 33

e.g. salmonellosis, E. coli, Toxoplasma gondii, etc.

Question 34

Vector-borne transmission: Vectors such as mosquitoes, ticks, fleas and lice can transmit zoonotic diseases to humans.

Give 3 examples of diseases that transmit in this way.

Answer 34

e.g. yellow fever, Kyasanur forest disease, plague, etc.

Question 35

Air-borne transmission: Air-borne transmission results from the inhalation of small particles (droplet nuclei) which are considered to have diameters 5 μm.

Give an example of a diseases that transmits in this way.

Answer 35

e.g. influenza viruses

Question 36

Indirect transmission through contaminated soil. Allowing the faeces to dry out and disintegrate contaminates the soil which increases the risk of exposure to pathogens.

Give an example of a pathogen that transmits in this way.

Answer 36

e.g. roundworm eggs can survive for years in contaminated soil

Question 37

Indirect transmission through contaminated water sources.

Give 4 examples of diseases that transmit in this way.

Answer 37

e.g. Cryptosporidium spp., cholera, rotavirus infection, leptospirosis, etc.

Question 38

In general, viruses account for a significant proportion of

Answer 38

emerging infectious diseases (EIDs).

and the majority have zoonotic origin

Question 39

what are considered the primary etiological agents of emerging infectious diseases?
and why?

Answer 39

These RNA viruses: ebolaviruses, human immunodeficiency virus (HIV), hantaviruses, Hendra and Nipah viruses, severe acute respiratory syndrome (SARS) coronavirus, influenza A viruses and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).

The RNA viruses are characterized by their rapid evolutionary rates due to the frequent error-prone replication cycles. so due to their higher ability to infect new host species with exceptionally short generation times they account for a significant portion of EIDs.

Question 40

Emerging Infectious Diseases are

Answer 40

the diseases that have not occurred before (e.g. SARS in 2003, COVID-19)

or have occurred previously but affected only small numbers of people in isolated places but now are rapidly increasing in incidence or geographical range (e.g. Zika was discovered in 1947 but the major epidemic was in 2015–2016)

or have occurred throughout the human history but only recently been recognized as a distinct disease due to infectious agent (e.g. the causative agent of Lyme disease was discovered in 1982).

Question 41

Re-emerging Infectious Diseases are

Answer 41

the diseases that were once major health problems globally or in a particular country, and then declined dramatically, but are again becoming health problems for a significant proportion of the population (e.g. malaria, rabies, cholera, tuberculosis).

Question 42

Neglected Zoonotic Diseases are

Answer 42

a subset of neglected tropical diseases. The term ‘neglected’ highlights that ‘these diseases affect mainly poor and marginalized populations in low-resource settings’.

Examples include rabies, echinococcosis, taeniasis/cysticercosis, schistosomiasis, etc.

Question 43

Transboundary Animal Diseases (TADs) are

Answer 43

These may be defined as those epidemic diseases which are highly contagious or transmissible and have the potential for very rapid spread, irrespective of national borders, causing serious socio-economic and possibly public health consequences.

Globalization, land encroachment and climate change contribute to outbreaks of such animal diseases, some of which are transmissible to humans, such as brucellosis, bovine tuberculosis, parasitic illnesses, anthrax, bovine spongiform encephalopathy and influenza viruses.

Question 44

An endemic is defined as

Answer 44

the habitual presence of a disease within a given geographic area.

It may also refer to the usual occurrence of a given disease within an area (e.g. rabies and brucellosis in India).

Question 45

An epidemic is defined as

Answer 45

the occurrence of disease above the normal expectancy in a region/country (e.g. Ebola outbreak in West African countries during 2014).

Question 46

A pandemic refers to

Answer 46

a worldwide epidemic covering larger geographical regions (e.g. H1N1 outbreak in 2009; COVID-19 outbreak of 2019–2021).

Question 47

define synanthrope

Answer 47

an undomesticated organism and especially an animal (such as a mouse, pigeon, or raccoon) that lives in close association with people and benefits from their surroundings and activities.

Question 48

Factors Responsible for the Emergence of Infectious Diseases (9)

Answer 48

1. Breakdown in public health measures (disasters, war etc.)
2. Increasing demand for animal protein
3. Unsustainable agricultural intensification
4. Increased use and exploitation of wildlife
5. Unsustainable utilization of natural resources accelerated by urbanization, land use change and extractive industries
6. Travel and transportation
7. Changes in food supply chains
8. Climate change
9. Microbial adaptation and changes