Johannesburg, (IRIN*) - Only 13 diseases or infections transmitted from animals to humans like tuberculosis (TB) and Rift Valley fever, are responsible for around 2.4 billion cases of human illness and 2.2 million deaths per year, mostly in low- and middle-income countries.
In the least developed countries, 20 percent of human sickness and death was due to zoonoses – diseases that had recently jumped species from animals to people – according to a new study by the International Livestock Research Institute (ILRI), based in Nairobi, Kenya, the Institute of Zoology in Britain, and the Hanoi School of Public Health in Vietnam.
The World Health Organization (WHO) has noted that at least 61 percent of all human diseases, and 75 percent of emerging infectious diseases, are zoonotic or caused by a bacterium, virus, fungus or other communicable disease agent picked up from an animal source.
While zoonoses can be transmitted to people by either wild or domesticated animals, and at times domestic animals also crossbreed with those in the wild, most human infections are acquired from the world’s 24 billion livestock, including pigs, poultry, cattle, goats, sheep and camels.
The new study mapped poverty, livestock-keeping, hunger and zoonoses, and found a strong link between them.
The Highest Number of Poor Livestock-keepers…and of Malnourished People
The good news is that most of the burden of zoonoses, and the opportunities for tackling them, are found in just a few countries – Ethiopia, Nigeria and India. These three countries not only have the highest number of poor livestock-keepers, but also the highest number of malnourished people.
Over 600 million people living on less than two dollars a day, who depend on animals to some extent, are found in South Asia, mostly in India. Sub-Saharan Africa has over 300 million poor livestock-keepers, concentrated in East and West Africa, and fewer in southern and central Africa.
In a survey of 28 countries identified as geographical hotpots for zoonoses by the study, Ethiopia tops the list of countries where Leptospirosis – haemorrhagic jaundice – is prevalent. Nigeria is saddled with the highest burden of Query fever (Q fever), a bacterial infection that can affect the lungs, liver, heart and other parts of the body.
|Why We Need to Worry about Zoonoses in Poor Countries|
|12 percent of animals have recent or current brucellosis infections, reducing production by 8 percent|
|10 percent of livestock in Africa are infected with trypanosomosis – sleeping sickness – reducing their production by 15 percent|
|7 percent of livestock are infected with tuberculosis (TB), reducing their production by 6 percent, and 3-10 percent of human TB cases may be caused by zoonotic TB|
|17 percent of pigs on smallholder farms show signs of current infection with cysticercosis – tapeworm – reducing their value and creating the enormous burden of human cysticercosis|
|27 percent of livestock show signs of current or past infection with bacterial food-borne diseases, a major source of food contamination and illness in people|
|26 percent of livestock show signs of current or past leptospirosis infection – affecting milk production and calving – reducing production and acting as a reservoir for infection|
|25 percent of livestock show signs of current or past Q fever infection|
Spontaneous Abortion in Animals; Severe Joint Pain and Weakness in Humans
India has a heavy burden of Brucellosis – which causes spontaneous abortion in animals, and in humans leads to severe joint pain and weakness, and can become chronic if untreated – as well as TB, Q fever, and illnesses caused by food-borne bacteria, such as salmonella, which can also be fatal.
The goal of the research was to identify areas where better control of zoonotic diseases would most benefit poor people.
Among the high-priority studies of transmitted diseases were ”endemic zoonoses” like brucellosis, which cause most cases of illness and recorded deaths in poor countries; “epidemic zoonoses”, which typically occur as outbreaks, such as anthrax and Rift Valley fever; and the relatively rare “emerging zoonoses” like bird flu. Of the emerging zoonoses, HIV/AIDS has had by far the most severe global impact.
A rising demand for milk and meat, prompted by a growing population and higher incomes in developing countries, has led to the practice of keeping more animals in smaller and often unhygienic enclosures – a major factor in the spread and growth of zoonoses.
The selection and breeding of livestock in these conditions, without proper care, creates an environment where a new pathogen (an infectious bacterium, virus or other agent) can develop and infect the animals. The study also found that systems for disease control and reporting were relatively weak in these countries.
Animals are often transported for long distances and over extensive routes, and sold live either along the way or at the destination, with poor waste management during transportation – which all contribute to the birth and transmission of infections.
Booming Trade in Poultry and Pigs
One of the biggest threats is posed by the booming trade in poultry and pigs. Ongoing research is being led by the International Food Policy Research Institute (IFPRI), which is part of a global research network funded partly by the Consultative Group on International Agricultural Research (CGIAR).
“Historically, high-density pig and poultry populations have been important in maintaining and mixing influenza populations,” said John McDermott, director of the CGIAR Research Programme on Agriculture for Nutrition and Health.
“A major concern is that as new livestock systems intensify, particularly in small- and medium-sized pig production, more intensive systems will allow the maintenance and transmission of pathogens. A number of new zoonoses, such as Nipah virus infections, have emerged in that way.”
Nipah virus, first identified on pig farms in Malaysia, and the related Hendra virus, which has particularly affected horses, can cause pneumonia and encephalitis in humans. A million pigs were culled in Malaysia to get rid of the virus.
Should We All Become Vegetarians?
More pigs and poultry “will lead to more, cheaper food, which is on the whole good for poor people. At the same time, they may lead to more disease, which is bad. Scientists can provide evidence, but societies need to have a conversation about the benefits, risks and trade-offs for keeping livestock,” Delia Grace, a researcher at the livestock research institute and lead author of the new study, told IRIN via email.
“We already have some ideas on how to do this. However, more livestock food (which could be milk and eggs, not just meat) has great potential in alleviating the ‘hidden hunger’ of micro-nutrient deficiency, which is such a huge problem in India and other countries.”
“For sure, there are both benefits and harms associated with producing any food type. It is important to factor in the cost of disease when assessing the benefits of more livestock, and to support systems which are “disease-proofed” – that is, designed in such a way as to minimize disease risks,” she noted.
Livestock can bring advantages. “At least one in two poor households benefits from livestock-keeping, and the benefits are big – [they can contribute from] 12 to 38 percent of household income. Our best estimates are that at least half the poor families get a quarter of their income from livestock – that’s big! Poor people don’t get much of their calories from livestock, but livestock products are not best used in providing calories – cheap staple foods, like rice, are better for that,” Grace pointed out.
“But livestock can provide high biological value protein, and vitamins and minerals that staple foods are deficient in. Hence, a contribution of 6-36 percent of total protein in the diet is quite important. But we certainly need more research on the appropriate role of livestock products in the diets of the poor, and especially of children. We are currently looking at which type of production is best for poor children’s nutrition: is it milk and dairy, or fish, or monogastric [animals with a single stomach, like pigs and poultry]?”
Public agricultural extension services to support farmers in developing countries need to step up to prevent the growth and transmission of zoonoses. “They [extension services] have been neglected and underfunded in many countries. There is also an important role for the media, and for NGOs and civil society. We find that many people in the food chain are ‘well-intentioned but ill-informed’, and big improvements are possible if people are given more information and simple solutions, like… cheap tests for food safety,” Grace said.
“The ongoing technology revolution offers great opportunity for this. For example, encouraging people to report diseases and get advice using special mobile phone apps [applications], or thermo-sensitive stickers that change colour if food is kept at the wrong temperature,” she wrote in her email.