Lecture 4 - animal pathogens 1 Flashcards
what are animal pathogens, where are they and why do we care?
Infectious agents that can cause disease in animals and humans.
everywhere
hey impact human welfare and a big economic impact on every country. (one health)
what are the costs of animal pathogens?
Billions of pounds each year is lost due to animal pathogens
health risks-
Fatal to animals/people
Foodborne illness
Poorly developed animals
Endemic disease
Economic risks-
Diagnostics
Vaccines and medicine
Market disruptions
Productivity losses
ECONOMIC IMPACT EXAMPLE - Consequences of UK Foot & Mouth Disease outbreak, 2001
~2,000 cases
~6 million animals culled
Consequences to tourism and transport due to control blocks in place. Leading to ~£8 billion loss in the economy
Changes in food security practices were introduced as a result of the outbreak
what are the 4 diseases of cattle?
Bovine tuberculosis - Bacteria
Trypanosomiasis (Nagana) - Parasite
Ringworm - Fungi
Rinderpest - Virus
what is bovine tuberculosis?
Mycobacterium bovis, part of the M. tuberculosis complex (MTB)
M. bovis infects cattle and other mammals
<1% human infections
M. tuberculosis: primary agent of human TB
M. avium: TB in birds but also opportunistic pathogen in AIDS patients
what is mycobacteria?
Phylum: Actinobacteria
Genus: Mycobacterium
Very slow replication (~20 hours)
Curved rod shaped
Gram positive… but hard to Gram stain (high surface lipid content)
Stains red with Acid-fast Ziehl-Neelsen (mycolic acids)
what are the symptoms of bovine tb?
Chronic disease that can take years to develop
Lymph nodes in the head are infected first, then tubercles (round lesions) appear on the surface of the chest cavity and lungs
Tubercles formed when immune cells engulf bacteria
Cattle show weakness, coughing and weight loss
Symptoms are rarely seen now due to the slaughter of infected animals
Cattle tested every 1-4 years and before farm movement
how does the pathogen evade the immune system?
Mycobacterium is an intracellular pathogen
- organism is phagocytosed into a vacuole called a phagosome
Phagosome fuses with lysosome
- phagolysosome
- low pH, reactive oxygen/nitrogen species
Usually kills bacteria…
but not Mycobacterium
how are mycobacteria killed?
Need activated macrophages to kill mycobacteria
Macrophage can be activated by immune molecules to change the phenotype.
how do mycobacteria evade the immune system? short term
Mycobacteria secrete protein and lipid factors
Block phagosome maturation
Prevent phagolysosome fusion
Resistant to Acidification and RNS/ROS
PtkA plays a direct role in acid inhibition
SigH, one of 12 MTB alternative sigma factors, is induced by heat, oxidative and nitric oxide stresses
Inhibits/Promotes Apoptosis and Autophagy
Depends on the strain virulence
how do mycobacteria evade the immune system in the long term
Lesions begin to form in undetected and chronic disease
Infected macrophages are phagocytosed by other macrophages.
An accumulation of macrophages leads to lesion formation.
Continues until death and is similar to human TB.
what is the historical perspective of the UK
Industrial revolution
Increased milk consumption
More intensive dairy farming
Humans consumed unpasteurised milk
In 1920, 50,000 new cases TB/year: 2,500 due to M. bovis
In 1930’s the government introduced new regulations as large proportion of dairy herds infected with M. bovis
Prevented consumer infection but not animal health issues
How is tb spread?
No country has managed to eradicate bovine TB without tackling wildlife reservoirs.
Many potential reservoirs (deer, fox, rodents…) but badgers are strongly implicated in transmission to cows.
is there a tb vaccination?
Humans can be vaccinated with attenuated M. bovis strain
- Bacillus Calmette-Guerin (BCG) strain
Huge investment in cattle and badger vaccine research
- DEFRA: >£23 million since 1998
£9.3 million additional funding for 2013-16
Injectable badger BCG vaccine licensed March 2010
Vaccine was expected in 2012 however, delayed due to problems.
- only 56 to 65% effective in Mexico/Ethiopia trials
- only useful as part of a range of measures
- results in positive diagnostic test (skin and blood test)
Develop new diagnostic – differentiate infected from vaccinated animals (DIVA) and change EU law relating to tests prior to trade.
Combinatorial approach will be required (vaccination, monitoring, culling, animal husbandry etc) to eradicate TB.
what are the costs of tb?
Thousands of new herd TB incidents every year
Cattle are slaughtered (reactors & close contacts)
6% (~5,000) of farms unable to move stock
Cost tax-payer £100 million to control TB
Compensation:
£68 for 3 month male calf dairy sector
£ 1,459 for female calved in dairy sector
£ 1,979 breeding bull, 20 months +, beef sector
£ 6,477 pedigree male 12-24 months, beef sector
Scotland was given ‘officially TB-free’ (OTF) status in 2009, but threat remains.
what is African animal trypanosomiasis?
Caused by trypanosomes, spread by tsetse fly (Glossina austeni)
Also known as N’gana (Nagana) – ‘powerless/useless’
Wasting parasitic disease of cattle & other livestock in sub-Saharan Africa
SYMPTOMS
Swelling
Fever
Reduced milk
Fertility issues
Weight loss
what are trypanosomes responsible?
Trypanosoma congolense
- most common organism
- resides in host blood vessels anaemia
Trypanosoma vivax
also found outside of tsetse belt
can spread independent of tsetse fly (needles, biting flies)
Trypanosoma brucei spp
- T. b. brucei only causes disease in animals
T. b. gambiense & T. b. rhodesiense also cause sleeping sickness in humans
what is trypanosomes disease?
Mostly a chronic disease but acute disease can be fatal in a week
Animals can be unapparent carriers
Domesticated animals often are more sensitive than wild
Effect on economy/health of the population
what is trypanosome immune evasion?
Antigenic variation
VSG (variant surface glycoprotein) switching
Trypanosomes first induce an immune response and then they change their antigen coat to prevent clearing.
what is ringworm?
Fungal infection of hair and keratinised layers of the skin, also known as dermatophytosis
Significant economic consequence to farmers
- hide damage
- growth rates reduced
Outbreaks in autumn/winter due to animals confined indoors
Zoonotic infection through direct contact/bites and largely occupational
what is treatment and prevention of trypnosomes?
No vaccine and it is difficult to develop
Drugs
diminazene aceturate (Berenil)
homidium bromide/chloride (Ethidium, Novidium)
isometamidium chloride (Samorin, Trypamidium)
New Trypano-tolerant cattle breeding
Vector control
traps
bush clearing
insecticides
sterile insect technique
what are trichophyton verrucosum?
Dermatophytes are slow growing organisms
- chlamydospores persist in environment
Self-limiting (-ish) disease
- treatment shortens the period of clinical signs
- disinfection of environment
- movement restrictions of livestock
There are vaccines available
- Onset of immunity at 3 weeks post-vaccination
Prevalent in pets
- Dogs and cats, especially kittens or puppies, can have ringworm that can be passed to people.
Notifiable disease in Norway
- vaccination significantly reduced outbreaks
what is rinderpest?
Acute, highly contagious viral disease of cattle, water buffalo & other wildlife
Devastating effects on agriculture throughout history in many parts of world
- In 1889, cattle from India introduced the virus into Africa
- 90% of African cattle were destroyed
- Led to mass starvation, killing a 1/3 of the population in Ethiopia
- Lack of grazing animals led to thickets tsetse flies increase
Most catastrophic natural disaster in Africa?
what is the rinderpest virus?
Paramyxoviridae; morbillivirus
- single stranded -ve sense RNA virus
- multiplies in host cells
- similar to measles virus
Spread through close contact
- highly contagious
- breath, secretions, excretions
- fever, diarrhoea, oral lesions
80-90% mortality rate, in days
Recovery can take weeks in animals that survive
what is immune suppresion?
Infected individuals develop a long-lasting specific immune response to morbilliviruses
Infected hosts suffer from transient generalised suppression of immune responses to other pathogens
- reduced B cells, monocytes, neutrophils and some types of T cells
- morbillivirus-infected individuals more likely to get a secondary infection
More is known about the response to the measles virus, assumed the same for Rinderpest
- acute infection leads to long-lasting specific immune response
- reduction in B cells unknown
how is it eradicated?
Only 2nd virus to be eradicated
Various attempts at control/eradication since 18th century
- slaughter
movement restrictions
vaccinations
Global eradication began in the 1980s
- cattle vaccination + simple diagnostic test
tissue culture Rinderpest vaccine (TCRV)
The last confirmed case in Kenya 2001
Eradication confirmed by WHO in June 2011
Virus still held in labs around the world
