Another Virus to Worry About

If you haven’t heard, there is currently a worldwide panic over the spread of a newly emerged coronavirus. This potentially lethal virus has caused a lot of disruption to global markets and is the reason why I can’t find hand sanitizer anywhere in town. But if you thought that the coronavirus was worrying, believe me, there are loads of other viruses to keep you up at night, and they don’t infect humans . . . they infect plants.

Plant viruses may not get as much attention in the media, but the consequences of plant viral infections can be just as dire, especially when the virus infects a crop. Take for instance the Cassava Mosaic Disease (CMD) pandemic of the 1990s. Cassava is a tropical tree cultivated mainly for its starchy tubers. It has become the third most important source of calories for people in the tropics, particularly Africa where it is a staple crop feeding ~700 million people each year. It is also a vital, reliable source of income for resource-poor farmers.

Cassava has a mortal enemy in the form of cassava mosaic disease (CMD), a viral disease that stunts cassava plants, twists and mottles their leaves and all but eliminates tuber production. CMD is caused by begomoviruses, a broad group of plant viruses that look two icosahedrons stuck together, and it is transferred from plant to plant by sap-sucking white flies. CMD was generally well-controlled in Africa, but in the 1980s, farmers in North-Central Uganda noticed the emergence of a new variety. 

The virus spread to the southern part of the country, devastating cassava plantations. By the 1990s, it had attacked 80% of Uganda’s cassavas, reducing its annual yield from 3.5 million tons to 0.5 million tons and costing the country $60 million dollars a year. The virus then spread to East and Central Africa and has since moved on to a least 12 other countries. The impact on Uganda, a country already ravaged by the AIDS epidemic and several wars, was terrible. In 1994 alone, 3,000 people died of famine-related illnesses that were blamed directly on CMD.

Since the 1990s, however, Uganda has rebounded. New, more resistant cassava varieties were painstakingly produced, but the CMD remains a constant foe and is now considered to be one of the most damaging crop viruses in the world. The 1990s CMD pandemic stands as a chilling reminder that a virus doesn’t need to give you the sniffles to completely destroy your world.

Sleep tight . . . .

Brian Rutter, PhD, is the cofounder of Thing in a Pot Productions and a postdoctoral researcher in plant biology at Indiana University. Subscribe to our newsletter to receive our “Things About Things – Odd Facts About Plants” and video production tips in your inbox every month!

Works Cited:
Alabi, Olufemi J., P. Lava Kumar, and Rayapati A. Naidu. “Cassava mosaic disease: a curse to food security in subSaharan Africa.” (2011).
Crawley, M. “Restoring Cassava Production in Uganda.”, 2010,, accessed 08 March 2020.
Ferreira, F. “Plant Viruses: An oft-forgotten threat to food security.” Harvard University The Graduate School of Arts and Sciences,, accessed on 08 March 2020.
Legg, J. P., and J. M. Thresh. “Cassava mosaic virus disease in East Africa: a dynamic disease in a changing environment.” Virus research 71.1-2 (2000): 135-149.
Legg, J., Somado, E.A., Barker, I. et al. A global alliance declaring war on cassava viruses in Africa. Food Sec.6, 231–248 (2014).
Jones, Roger AC, and Rayapati A. Naidu. “Global dimensions of plant virus diseases: Current status and future perspectives.” Annual review of virology 6 (2019): 387-409.

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