Strong 'one-health' connection exists between humans, livestock

For every 10 cases of animal sickness or death, the incidence of human disease increased by 31% in the same household, according to a recent epidemiological investigation of the health of farmers and their livestock in rural Kenya.

“Our findings help to understand, in quantitative terms, the complex pathways that link livestock health to the health and welfare of the humans who own them,” Thumbi Mwangi, BVM, MSc, PhD, a Kenyan native and infectious disease epidemiologist at Washington State University’s Paul G. Allen School for Global Animal Health, said in a press release. “It’s important because an estimated 300 million people living in sub-Saharan Africa depend on their livestock as a main source of livelihood and nutrition.”

Starting in February 2013, Mwangi and colleagues tracked 1,500 households and their livestock in 10 western Kenyan villages. Through face-to-face and mobile telephone interviews, the researchers collected data on four human syndromes — fever, jaundice, diarrhea and respiratory illness — as well as nine animal syndromes found in the household’s livestock. In addition, socioeconomic surveys were carried out for each household every 3 months. The present analysis included more than 6,400 adults and children, 8,000 cattle, 2,400 goats, 1,300 sheep and 18,000 chickens.

During the first year of the study, 93% of households owned at least one type of livestock, including chicken (88%), cattle (55%), goats (41%) and sheep (19%).

Digestive disorders, primarily diarrhea, were the most common syndromes observed in livestock (56%), followed by respiratory illness (18%), according to the researchers. Respiratory illness (54%) was the most common syndrome in humans, followed by fever (40%) and diarrhea (5%).

After adjusting for the size of the household, Mwangi and colleagues found that human illness increased 1.31-fold (95% CI, 1.16-1.49) for every 10 cases of animal illness or death.

“Additionally, for the common respiratory and gastrointestinal illnesses, households with high numbers of animal cases of each of these respective syndromes have high numbers of the similar syndromes in humans,” the researchers wrote.

Specifically, there was a 6% increase (95% CI, 2-12) in the probability of gastrointestinal illness and a 10% increase (95% CI, 4-17) in the probability of respiratory illness in humans associated with each additional case of these syndromes in animals, according to the research.

Mwangi and colleagues theorize that cases of human illness observed in the study were either the result of zoonotic transmission or “may be related to the environment in which the humans and animals co-reside,” although this will be investigated further, they wrote.

“Although we have not in the current study investigated whether pathogens causing diseases in people have been acquired from their animals, we have data from our other studies showing some zoonotic diseases such as brucellosis are very common in certain rural settings — both in people and in their animals,” Mwangi told Infectious Disease News.

Mwangi added that these diseases can present with similar clinical signs of better known diseases, including malaria.

“The clinician dealing with diseases in a tropical setting may need to consider a wider differential diagnosis for their patients, including neglected zoonotic diseases, which continue to exert burden on people and are easily missed by routine diagnostic tests … ” he said.

The researchers also found evidence that the likelihood of an ill household member seeking health care increased with the number of livestock they owned — 1.15 times (95% CI, 1.03-1.29) for every 10 cattle — suggesting a connection between livestock ownership, income and better access to health care.

According to Mwangi and colleagues, human and animal health primarily intersect in three areas:

• socioeconomically, where improved livestock production leads to improved household incomes, access to education and health care;
• nutritionally, where owning healthy livestock is associated with increased access to food and a reduced risk for malnutrition and disease; and
• zoonotically, where healthy livestock are less likely to transmit pathogens to humans.

“These data allow for the investigation, understanding and quantification of the pathways by which human health and welfare are linked to animal health, and provide a platform for testing hypotheses related to “one-health,” including scientific enquiries focusing on specific diseases, coinfections and their interactions,” the researchers wrote, adding that further study of interventions in animals to control human disease can help shape policy and investment in resource-poor areas. – by John Schoen

Disclosure: The researchers report no relevant financial disclosures.