Lethal family tree: ILRI research shows livestock bacterium is as old as the livestock it kills

Aurochs were the ancestors of domestic cattle (photo on Flickr by Marcus Sümnick).

Lucas Brouwers, in a blog on Scientific American, has picked up on an interesting genetics study conducted at the International Livestock Research Institute (ILRI), in Nairobi, Kenya, which targets a cattle disease known as contagious bovine pleuropneumonia (or CBPP for short). The study provides evidence of the primeval origins of the arms race between pathogens and their animal hosts.

The study, conducted by ILRI researchers and partners at the International Centre of Insect Physiology and Ecology (also in Nairobi), and in Germany, Sweden, Switzerland and the USA, was published last month in the Public Library of Science (PLoS, 27 Apr 2012).

The study shows that some ten thousand years ago, as humans first began to domesticate species of wild ruminants (in Africa as well as the Near East), they unwittingly also began to domesticate a wild bacterium—Mycoplasma mycoides.

‘. . . This bacterium has left a long and bloody trail through livestock history. Virulent strains of Mycoplasma raged around the world in the 19th century, killing millions of goats and cows. But the roots of Mycoplasma mycoides run deeper. In their paper, Anne Fischer and her colleagues show that the entire Mycoplasma mycoides cluster arose 10,000 years ago.

Mycoplasma mycoides is as old as the livestock it kills.

‘A severe Mycoplasma infection begins with a cough, followed by a groan, a grunt and more coughing. Breathing becomes difficult and painful. Eventually, the cow or goat becomes listless and, in the terminal stage of disease, stops moving altogether. . . . Untreated, the most deadly of Mycoplasma strains can slaughter herds within days. . . .

‘The nineteenth century . . . was a golden age, as far as Mycoplasma mycoides was concerned. The livestock trade became global, while vaccination programmes were still in their infancy. Entire countries could be infected by a single animal. . . . [A] handful of cows in . . . [South Africa] became infected by a Friesian bull, imported from the Netherlands. The disease soon swept through South Africa, killing 100.000 cows and oxen along the way.

‘To be fair, not every strain of Mycoplasma mycoides is a killer, and not every infection ends in death. The Mycoplasma family is large and most strains are not as lethal as Mycoplasma mycoides mycoides (for cows) and Mycoplasma capricolum capripneumoniae (for goats), the two strains that cause the contagious pneumonia described above.

‘Over the past few years, scientists have realized that the Mycoplasma mycoides family extends beyond its two most infamous members, but have so far failed to chart all the relationships between the different strains. To figure out who is related to whom, Anne Fischer and her colleagues collected 118 different strains from all over the world, and sequenced 7 of their genes. Fischer’s collection features bacteria from all times and places, including strains isolated from African cattle in 1931, Rocky Mountain goats and Mouflons from Qatar.

‘Using the genetic differences between strains as a measure for their kinship, Fischer’s team reconstructed the entire Mycoplasma mycoides family tree. From this tree, the team concludes that the founding father of all Mycoplasma mycoides lived 10,000 years ago—around the same time pastoralists domesticated cattle, goats and sheep in the Near East. . . .

The family tree of the Mycoplasma mycoides cluster, published in the 2012 paper by Fischer et al. Horizontal axis represents time, in years before present. The entire cluster is 10,000 years old, but the two most virulent strains (M caprcicolum subsp capripneumoniae and M mycoides subsp mycoides) are much younger.

‘While Mycoplasma mycoides as a family might be as ancient as livestock itself, the two most contagious and deadly strains are much younger. The common ancestors of the strains that cause contagious pneumonia in cows and goats lived between 91 and 414 and between 56 and 490 years ago, respectively. . . . [W]hat could have favoured the origin and survival of these hypervirulent bugs in recent centuries. Herding made Mycoplasma mycoides—but what turned it into a killer?’

Read the whole post by Lucas Brouwers on Scientific American‘s Thoughtomics Blog: Livestock bacteria are as old as the livestock they kill, 14 May  2012.

Read the science paper: The origin of the Mycoplasma mycoides cluster coincides with domestication of ruminants, by Anne Fischer (ICIPE and ILRI), Beth Shapiro (Pennsylvania State University), Cecilia Muriuki (ILRI), Martin Heller (Friedrich-Loeffler-Institute), Christiane Schnee (Friedrich-Loeffler-Institute), Erik Bongcam-Rudloff (Swedish University of Agricultural Sciences), Joachim Frey (University of Berne) and Joerg Jores (ILRI), 2012, PLoS ONE 7(4): e36150.