Introduction - What are zoonoses?
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Introduction - What are zoonoses?
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Healthy animals, healthy people!
A herd or flock will be of benefit to its owners if it is healthy, because
healthy animals grow faster and produce more food and more draught
power. Some animal diseases and parasites may not only make the
animals ill, they can be a threat to humans as well. These diseases are
called zoonotic diseases or zoonoses.
When animals fall ill, the owner has a problem because many owners
depend on their animals for income. If a sick donkey cannot pull the
cart to bring fruits to the market, there will be no income (for the family).
If sick chickens stop laying eggs, there will be no eggs to sell.
And without any money, how can sick animals be treated or replaced
if they die?
Some animal diseases can spread to other animals making the problems
even bigger. Worse still, the disease can also spread to humans.
In recent years, much publicity has been focused on mad cow disease
(BSE) and avian influenza (AI). While these zoonoses are described as
serious threats to human health, many other zoonoses cause more
deaths among people (especially in developing countries) and get far
less attention. Rabies, for example, kills around 55,000 people worldwide
each year, while in comparison BSE killed (only) 139 people
between 1996 and 2002. Human deaths due to avian influenza have
amounted to no more than 200 worldwide (Source: WHO Fact Sheets,
2007). Many of these zoonoses can be entirely prevented (though not
easily!).
Our information in this Agrodok is on Zoonoses, focusing on the prevention
of zoonoses in humans (and not in animals). However, to prevent
these diseases from occurring in humans, you will also - as far as
possible - need to prevent them occurring in animals.
What are zoonoses?
The definition we use here for zoonoses (or zoonotic diseases) is as
follows:
| Infectious diseases that can be transmitted between animals and humans, and may give problems in humans but not necessarily in animals. |
Infectious diseases are caused by pathogenic microbes (viruses, bacteria)
or by parasites (worms, protozoans). The microbe or parasite infects
the animal or human and causes disease.
Microbes and parasites can be found in different places in the body,
depending on the disease. Some live in the intestines and others in
organs. Microbes and parasites can also be present in the urine, blood,
faeces and saliva. For instance, when you cough, small droplets of
saliva can be projected through the air to anyone in the immediate vicinity,
and if you are ill, the microbes in your saliva can infect people.
Diseases that cause diarrhoea are another example.
An animal may be a carrier of a specific microbe or parasite. This
means it carries the microbe or parasite but is not ill. Still, the animal
can spread microbes like salmonella, for instance, via its excreta.
Infectious diseases caused by zoonoses are specific: they are not restricted
to one animal species or solely to humans, and can cross over
from animals to humans and vice versa (action known as transmission).
More information about the different routes by which zoonoses
can be transmitted from animals to humans can be found in the chapter "How people get infected:
transmission and risk factors"
Some zoonoses cause no signs of disease in animals. An example is
porcine cysticercosis (see Section 6.6). Cysticercosis is caused by the
young form (larva) of the pig tapeworm. In humans, cysticercosis may
cause epileptic fits or large nodules under the skin, while the infected
pig will show no signs or symptoms of the disease, except for some
vesicles on the tongue.
Some well-known diseases are commonly thought to be zoonotic,
whereas they are not. For example, classical (CSF) and African swine
fever (ASF) do NOT cause illness in humans. The same goes for Foot
and Mouth Disease (FMD).
| Box 1: Different concepts of health and disease
What is a healthy person? When is someone ill? These questions are answered
differently in different parts of the world. In other words: "health" and
"disease" are strongly culturally and socially influenced. In many societies diseases
are even believed to be punishment from the gods or caused by "black
magic".
Some preventive measures may be difficult to implement in a community simply
because they require a new way of thinking or new habits. And changing
habits is extremely difficult.
In this book we concentrate on diseases that can be spread by infection with
microbes and parasites.
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Why is knowledge of zoonoses important?
Knowledge of zoonoses is of importance to people who live in close
contact with animals and to those who work with animals or animal
products. Most zoonoses can be prevented by simple measures like
vaccination of animals or by proper heating of food, for example. Prevention
of zoonoses will improve the health of animals, the income of
their owners, and the health of people.
Most zoonotic diseases occur in developing countries and in poor rural
communities. Prevention of zoonoses in animals and humans can be a
tool in the fight against poverty!
| Box 2: Zoonoses and the World Health Organization
In 2005, the World Health Organization organized a meeting about zoonotic
diseases because governments, non-governmental organizations and donors
often overlook them. These institutions need to prioritize their efforts and focus
on the control of "the big three" - human tuberculosis, malaria and HIV/AIDS.
Especially in poor agricultural communities, "neglected" zoonoses have a major
impact on the well being of people. The document issued after the meeting
states: "These diseases play a key role in perpetuating poverty" and
"zoonoses control can be a cost-effective opportunity for poverty alleviation".
Source: The Control of Neglected Zoonotic Diseases: a route to poverty alleviation:
report of a joint WHO/DFID-AHP meeting.
ISBN 92 4 159430 6. |