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Zoonotic transmission of tuberculosis – the importance of a One Health approach
1. Animal-to-human transmission
of Mycobacterium tuberculosis
Erin Passmore1, Mark Ferson1,2, Siranda Torvaldsen1
1 School of Public Health and Community Medicine, University of
New South Wales, Australia
2 Public Health Unit, South East Sydney Local Health District, New
South Wales, Australia
2.
3.
4. 1. How often does animal-to-human
transmission of M. tuberculosis
occur?
2. Who is most at risk?
5. Transmission in animal facilities
• Six articles described M. tuberculosis
transmission in zoos/refuges
• Two articles described M. tuberculosis
transmission during necropsies
• Index case: wild animals (e.g.
elephant, rhino, chimpanzee) and domestic
pets
6. How often does animal-tohuman transmission of M.
tuberculosis occur?
7. • 8 outbreak investigations
• Of 567 people screened (range 10-307):
– Total 103 people with latent TB infection (range
12%-50%)
– 2 people with active TB disease
• Limitations
– No proof that the people with latent TB infection
were infected by the animal with TB
8. Question: How often does animal-tohuman transmission of M.
tuberculosis occur?
Answer: Rarely. But the research has
many limitations.
10. 1. Close contact with animals with TB
• Two studies found increased
risk of latent TB infection in
staff who have direct
physical contact with an
animal with TB (e.g.
trainers, handlers)
• Consistent with human
model of TB transmission
• Long recognised that
primate caretakers in zoo
and laboratory settings at
increased risk of M.
tuberculosis infection
11. 2. Necropsy
• Four studies identified an
increased risk of latent TB
infection in people who
performed or attended
necropsies of animals with TB
• Consistent with increased risk of
M. tuberculosis infection in
human autopsy personnel
• Linked to use of equipment that
aerosolises infectious particles
(e.g. saws)
12. 3. Aerosol-generating work activities
• Two studies identified
increased risk of latent TB
infection in staff who cleaned
areas used by infected animals
• Hypothesis: animal waste
containing M. tuberculosis
aerosolised during cleaning
(e.g. pressure
hosing, sweeping) and inhaled
• Aerosolisation implicated in
outbreaks in human healthcare
settings (e.g. medical waste)
13. Who is most at risk?
• Three key activities associated with
transmission: direct close contact, necropsies,
aerosol-generating work activities
• Indirect aerosolisation and environmental
contamination may have a greater role in
animal-to-human transmission than it does in
human-to-human transmission
• Need for higher quality studies
In my first presentation, I described how TB is mainly a human disease, but can also be transmitted from humans to animals, between animals, and from animals to humans. In this presentation, I will look more closely about transmission of TB from animals to humans.
Several times each year, there are reports in the media of zoo animals – usually elephants – having tuberculosis. For example, this year an elephant at Oregon Zoo was diagnosed with TB, and in the last few years there has been substantial media coverage around an elephant and a chimpanzee diagnosed with TB at Taronga Zoo in Sydney, 2 elephants at Lyon Zoo in France, and many others.Every time a new case is reported, it raises important questions about whether an animal with TB poses a risk to human health.
Work in this area has focussed on two questions:How often do animals transmit TB to humans?What activities put people at risk?To answer these questions, I did a comprehensive literature review searching for any reports of animal to human transmission of TB – including searching academic databases, google and asking experts.As mentioned in my first presentation, there are five mycobacteria that cause TB, but my work has focussed on Mycobacterium tuberculosis, which causes TB in humans.
I’ve found eight reports of animal to human transmission of TB – 6 articles describing transmission at zoos and refuges, and two describing transmission at necropsy.The animal “index” cases that prompted the investigations were wild animals (such as elephants, rhinos, chimpanzees) and domestic pets.The articles reported outcomes of screening humans who had contact with the animal with TB, such as zoo keepers and pet owners.
The second question I sought to answer was “who is most at risk” of getting TB from an animal.Keeping in mind the limitations of the evidence, I identified three groups of people that seem to be most at risk.