chapter 12 p2

Question 1

animal diseases

Answer 1

A
The diseases that affect animals - and in particular human beings - have a profound effect on human health and wellbeing - and on national economies.
Communicable diseases range from mild to fatal.

Examples include:
. Tuberculosis (TB)
Bacterial meningitis
. HIV/AIDS (acquired immunodeficiency syndrome)
Influenza (flu)
Malaria
. Ring worm
Athlete’s foot

Question 2

Tuberculosis (TB

Answer 2

• A bacterial disease of humans, cows, pigs, badgers, and deer commonly caused by Mycobacterium tuberculosis and M. bovis.
• TB damages and destroys lung tissue and suppresses the immune system, so the body is less able to fight off other diseases.
• The global rise of HIV/AIDS has had a big impact on the numbers of people also suffering from diseases such as TB, because people affected by HIV/AIDS are much more likely to develop TB infections.
• In people TB is both curable (by antibiotics) and preventable (by improving living standards and vaccination).

Question 3

TB, cows, and badgers:

Answer 3

• TB affects animal populations.
• In 2013, almost 33 000 UK cattle were destroyed because they were infected with bovine TB.
• There is clear evidence that TB is passed from wild animals, such as badgers or possums, to cattle, and vice versa.
• This presents a problem as cattle can be tested and culled, but it is very difficult to prevent them becoming re-infected from wildlife, particularly when they are out at pasture.
• Scientists are still unsure how this wildlife infection can best be controlled.
• One method is to cull the wildlife source - in countries where this has been done, TB rates in cattle have fallen substantially, however it must be carried out carefully and thoroughly or it can lead to greater disease spread as animals are dispersed.
• Some people, however, feel culling is not an acceptable approach and vaccination of either cattle or the wild animals is a better route.
• The test for TB cannot currently distinguish between an infected animal and a vaccinated animal, so current EU law bans cattle vaccines.
• Research is continuing on an improved version of both the vaccine and test.
• Vaccinating a population of wild animals is not an easy task, and it is as yet an unproven method to control the spread of disease.
• The problem of TB in animals will not be solved easily, but the research and the debate continues.

Question 4

Bacterial meningitis

Answer 4

• a bacterial infection (commonly Streptococcus pneumoniae or Neisseria meningitidis) of the meninges of the brain (protective membranes on the surface of the brain), which can spread into the rest of the body causing septicaemia (blood poisoning) and rapid death.
• It mainly affects very young children and teenagers aged 15-19.
• They have different symptoms but in both, a blotchy red/purple rash that does not disappear when a glass is pressed against it is a symptom of septicaemia and immediate medical treatment is needed.
• About 10% of people infected will die.
• Up to 25% of those who recover have some permanent damage.
• Antibiotics will cure the disease if delivered early.
• Vaccines can protect against some forms of bacterial meningitis.

Question 5

HIV/AIDS (acquired immunodeficiency syndrome)
p1

Answer 5

• caused by HIV(human immunodeficiency virus), which targets T helper cells in the immune system of the body
• It gradually destroys the immune system so affected people are open to other infections, such as TB and pneumonia, as well as some types of cancer.
• HIV/AIDS can affect humans and some non-human primates.
• HIV is a retrovirus with RNA as its genetic material.
• It contains the enzyme reverse transcriptase, which transcribes the RNA to a single strand of DNA to produce a single strand of DNA in the host cell.
• This DNA interacts with the genetic material of the host cell.
• The virus is passed from one person to another in bodily fluids, most commonly through unprotected sex, shared needles, contaminated blood products and from mothers to their babies during pregnancy. birth or breast feeding.

Question 6

HIV/AIDS (acquired immunodeficiency syndrome)
p2

Answer 6

• There is as yet no vaccine and no cure, but anti-retroviral drugs slow the progress of the disease to give many years of healthy life.
• Girls and women are at particularly high risk of HIV/AIDS in many countries.
• Traditional practices such as female genital mutilation (FGM) increase the infection rate - if the same equipment is used multiple times then this can spread the infection, in addition, women who have undergone FGM are also more vulnerable to infection during intercourse.
• Sub-Saharan Africa is the region worst affected by HIV/AIDS
• This disease has massive social and economic consequences as well as the personal impact to each person infected.

Question 7

Influenza (flu)

Answer 7

• a viral infection (Orthomyxoviridae spp.) of the ciliated epithelial cells in the gas exchange system.
• It kills them, leaving the airways open to secondary infection.
• Flu can be fatal, especially to young children, old people and people with chronic illnesses.
• Many of these deaths are from severe secondary bacterial infections such as pneumonia on top of the original viral infection.
• Flu affects mammals, including humans and pigs, and birds, including chickens.
• There are three main strains - A, B and C.
• Strain A viruses are the most virulent and they are classified further by the proteins on their surfaces, for example A(HIN1) and A(H3N3).
• Flu viruses mutate regularly.
• The change is usually quite small, so having flu one year leaves you with some immunity for the next.
• Every so often, however there is a major change in the surface antigens and this heralds a flu epidemic or pandemic as there are no antibodies available.
• Vulnerable groups are given a flu vaccine annually to protect against ever changing strains.
• There is no cure.

Question 8

Zoonotic Influenza:

Answer 8

• A disease which people can catch from animals is known as a zoonosis.
• Influenza, for example attacks a range of animals including birds and pigs.
• Sometimes the virus which causes bird flu or swine (pig) flu mutates and becomes capable of infecting people.
• These new strains can be particularly serious, because few people have any natural immunity to them.
• In March 2009 60% of the population of a small town in Mexico became infected with a new disease and two babies died.
• Some of those infected tested positive for H1N1, a form of flu usually found in pigs, rather than the usual human flu strains.
• The H1N1 virus which caused a flu pandemic in 2009
• The outbreak spread to the US, where using DNA analysis techniques, the virus was identified as a new mutant strain of the H1N1 swine flu virus, which had not been seen before in either pigs or people.
• Three months after it first appeared people were infected with H1N1 flu in 62 countries, and some of them were dying.
• None of the available flu vaccines were any use against this zoonotic virus.
• Within five months almost 3000 people around the world had died.
• Fortunately, only six months after swine flu H1N1 was first identified, scientists produced an effective vaccine.
• In spite of this, recent analyses of the data suggest between 200 000-300 000 people died as a result of H1N1 infection in the 2009 outbreak - and up to 80% of those deaths were in people aged 65 and younger.
• In a normal seasonal flu outbreak, only around 10% of deaths occur in people who are under 65.
• H1N1 is now part of the normal seasonal flu vaccine and scientists remain on the lookout for the next mutation which may enable the flu virus to pass from pigs or birds to people, known as a species jump.

Question 9

Malaria

Answer 9

• caused by the protoctista Plasmodium and spread by the bites of infected Anopheles mosquitoes
• The Plasmodium parasite has a complex life cycle with two hosts - mosquitoes and people.
• They reproduce inside the female mosquito.
• The female needs to take two blood meals to provide her with protein before she lays her eggs - and this is when Plasmodium is passed on to people.
• It invades the red blood cells, liver, and even the brain.
• The disease recurs, making people weak and vulnerable to other infections.
• There is no vaccine against malaria and limited cures, but preventative measures can very effective - The key is to control the vector.
• Anopheles mosquitoes can be destroyed by insecticides and by removing the standing water where they breed.
• Simple measures such as mosquito nets, window and door screens and long sleeved clothing can prevent them biting people and spreading the disease.

Question 10

Ring worm

Answer 10

a fungal disease affecting mammals including cattle, dogs, cats and humans.
Different fungi infect different species - in cattle, ring worm is usually caused by Trichophyton verrucosum.
It causes grey-white, crusty, infectious, circular areas of skin.
It is not damaging but looks unsightly and may be itchy. Antifungal creams are an effective cure.

Question 11

Athlete’s foot

Answer 11

a human fungal disease caused by Tinia pedia, a form of human ring worm that grows on and digests the warm, moist skin between the toes.
It causes cracking and scaling. which is itchy and may become sore.
Antifungal creams are an effective cure.

Question 12

Identifying pathogens:

Answer 12

When an outbreak of a disease occurs in plants or animals, the key to successful control or cure is to identify the pathogens involved.
Our ability to do this has increased along with our understanding of the causes of disease and developments in technology:

Question 13

Our ability to do this has increased along with our understanding of the causes of disease and developments in technology:

Answer 13

• Traditionally pathogens were cultured in the laboratory and identified using a microscope.
• Monoclonal antibodies (antibodies made by cells of the immune system that recognise one specific antigen) can be used now to identify pathogenic organisms in both plants and animals
• DNA sequencing technology means pathogens can be identified precisely, down to a single mutation (see Zoonotic influenza).

Question 14

Case study:

Answer 14

In a transplant ward, four patients developed infections caused by methicillin resistant Staphylococcus aureus (MRSA).
If the bacterium was being transmitted to patients by a member of staff, this was a serious outbreak.
But DNA sequencing at the Sanger Institute gave rapid results - new technology means a bacterial genome can be sequenced in less than 24 hours.
Researchers showed that each of the patients had a different strain of MRSA.
The cases were not linked, so it was not a hospital-based outbreak requiring staff to be screened or treated.

Question 15

The transmission of communicable diseases

Answer 15

For the pathogens that cause communicable diseases to be successful, they have to be transmissible.
So how are pathogenic bacteria, viruses, protoctista, and fungi transmitted from one host to another?

Question 16

Transmission of pathogens between animals:
Understanding how diseases are transmitted from one individual to another allows us to work out ways to reduce or prevent it happening.

two main types of transmission

Answer 16

direct transmission and indirect transmission.

Question 17

Direct contact

Answer 17

• (contagious diseases):
• kissing or any contact with the body fluids of another person, for example, bacterial meningitis and many sexually transmitted diseases
• direct skin-to-skin contact, for example, ring worm, athlete’s foot
• microorganisms from faces transmitted on the hands, for example, diarrhoeal diseases.

Inoculation:
Ingestion:

Question 18

Inoculation:

Answer 18

through a break in the skin, for example, during sex (HIV/AIDS)
from an animal bite, for example, rabies
through a puncture wound or through sharing needles, e.g. septicaemia.

Question 19

Ingestion:

Answer 19

taking in contaminated food or drink, or transferring pathogens to the mouth from the hands, for example, amoebic dysentery, diarrhoeal diseases.

Question 20

Indirect transmission

Answer 20

inanimate objects such as bedding. socks, or cosmetics can transfer pathogens, for example, athlete’s foot, gas gangrene and Staphylococcus infections.

Fomites:
Droplet infection (inhalation):
Vectors:

Question 21

Fomites

Answer 21

inanimate objects such as bedding. socks, or cosmetics can transfer pathogens, for example, athlete’s foot, gas gangrene and Staphylococcus infections.

Question 22

Droplet infection (inhalation):

Answer 22

Minute droplets of saliva and mucus are expelled from your mouth as you talk, cough or sneeze.
If these droplets contain pathogens, when healthy individuals breathe the droplets in they may become infected, for example, influenza, tuberculosis.

Question 23

Vectors:

Answer 23

A vector transmits communicable pathogens from one host to another.
Vectors are often but not always animals, for example, mosquitoes transmit malaria, rat fleas transmit bubonic plague, dogs, foxes and bats transmit rabies.

Water can also act as a vector of disease, for example, diarrhoeal diseases.

Question 24

Transmission between animals and humans

Answer 24

Some communicable diseases can be passed from animals to people, for example the bird flu strain HIN1 and brucellosis, which is passed from sheep to people.
Minimising close contact with animals and washing hands thoroughly following any such contact can reduce infection rates.
People can also act as vectors of some animal diseases, sometimes with fatal results, for example foot-and-mouth disease.

Question 25

Factors affecting the transmission of communicable diseases in animals:

Answer 25

1. overcrowded living and working conditions 2. poor nutrition 3. a compromised immune system, including (in humans) having HIV/ AIDS or needing immunosuppressant drugs after transplant surgery 4. (in humans) poor disposal of waste, providing breeding sites for vectors 5. climate change - this can introduce new vectors and new diseases. for example increased temperatures promote the spread of malaria as the vector mosquito species is able to survive over a wider area 6. Culture and infrastructure - in many countries traditional medical practises can increase transmission 7. Socioeconomic factors - for example, a lack of trained health workers and insufficient public warning when there is an outbreak of disease can also affect transmission rates.

Question 26

Transmission of pathogens between plants:

Answer 26

Plants do not move around, cough or sneeze, yet diseases spread rapidly through plant communities, plant pollen and seed, for example move widely. Plants also have a less well developed immune system than humans.

Question 27

Direct transmission in plants

Answer 27

This involves direct contact of a healthy plant with any part of a diseased plant. Examples are ring rot, tobacco mosaic virus (TV), tomato and potato blight, and black sigatoka.

Question 28

Indirect transmission in plants

Answer 28

Soil contamination vectors

Question 29

Soil contamination

Answer 29

Infected plants often leave pathogens (bacteria or viruses) or reproductive spores from protoctista or fungi in the soil. These can infect the next crop. Examples are black sigatoka spores, ring rot bacteria, spores of P. infestans and MV. Some pathogens (often as spores) can survive the composting process so the infection cycle can be completed when contaminated compost is used.