Potato Blight: Fairness and Famine

Aliases: potato blight, late blight

The Irish Potato Famine infamously upended a nation. In the wake of a series of blight-plagued potato crop failures from 1845 to 1850, Ireland lost over a quarter of its population. During the Famine, 1.5 million Irish died of starvation or related disease, and nearly the same number emigrated to other countries.4 The Famine arguably changed the course of history, and it stands as a stark reminder of the consequences of social oppression, and fragility of the agricultural systems we depend on.

The British colonization of Ireland left the Irish peasantry disenfranchised and landless. In order to eke out a living, they were forced to live in close quarters and farm whatever land they could reclaim. The potato became critical to survival, as it produced high calories and fairly good nutrition in a small plot of land (only a ¼ of what wheat or other grains require). By the mid-1840s up to ½ of the Irish population depended on potatoes; they were an essential food source for peasant families.2 Prior to the Famine, the average Irish man ate 12 pounds of potatoes a day.4

The concentration and poverty of the peasant population resulted not only in human suffering, it also created the ideal conditions for a potato pathogen to spread. Because potatoes were so important, they were everywhere, providing ample biomass for disease to attack. Their ubiquity also forced potato fields close together, allowing for easy spread across the landscape. Finally, there was little genetic diversity in the potatoes grown by the peasantry, who did not have access to global markets, making their crops particularly vulnerable to disease.3

The blight swept through, devastating Ireland2, and it may not be done yet. Potato blight has recently reemerged, reaching epidemic levels in North America and Europe, despite greater awareness and precautions. And again, humans are not blameless. This renewed vigor is in part the result of growing fungicide resistance in the pathogen, following over a century of heavy use.4 It turns out, even knowing history’s mistakes, there are still plenty of new ones we can make.

potato blight
I have nothing witty to say. Erin go Bragh!

Cause: Potato blight is caused by the nefariously named Phytophthora infestans, an oomycete. (Oomyocetes appear similar to fungi, but unlike true fungi, they contain cellulose rather than chitin in their cell walls and produce motile zoospores. They are actually more closely related to brown algae. And now you know). The exact geographic source of the pathogen is still unknown4; regardless, it travels fast. Its spores are easily transmitted by wind and water, and germinate almost as soon as they land on a host plant.2 The pathogen can also be transferred large distances in infected plant tissue.4

Consequence: Blight causes an array of symptoms in infected potato and tomato plants (Surprise! The pathogen is also devastating in tomatoes), including wilting, chlorosis (the insufficient production of chlorophyll), and the rotting of roots and other organs.1 The results of this can be catastrophic, leading to partial or total crop failure.

Cure: The preventative use of fungicides (anti-fungal chemicals) has been the only consistently successful containment measure for potato blight. In many major production regions, potatoes cannot be grown without fungicide. But this security comes at a high price: in 1995, blight control was estimated to cost more than US$30 million in the Columbia potato-growing region of Washington and Oregon alone. Heavy fungicide use has also spurred the evolution of fungicide-resistant strains of blight, which can wreak havoc on crops.4 Sometimes you really can’t win for losing.


  1. Akino, S, D Takemoto, & K Hosaka. 2014. Phytophthora infestans: a review of past and current studies on potato late blight. Journal of General Plant Pathology, 80:24-37.
  1. Braa, DM. 1997. The great potato famine and the transformation of Irish peasant society. Science & Society, 61:193-215.
  1. Fraser, EDG. 2003. Social vulnerability and ecological fragility: building bridges between social and natural sciences using the Irish Potato Famine as a case study. Conservation Ecology, 7:9.
  1. Ristaino, JB. 2002. Tracking historic migrations of the Irish potato famine pathogen, Phytophthora infestans. Microbes and Infection, 4:1369-1377.

Image source: Creative Commons, https://en.wikipedia.org/wiki/Great_Famine_(Ireland)

Livestock and Disease: Intense

Domesticated animals and livestock have been essential to the slow but unceasing progression of human civilization; they’ve been our companions, our work force, and our fuel. While our relationship has been overwhelming positive (at least for us– we’re not the ones being eaten, after all), it’s comforts come at a cost. Animals sustain us, but they can also carry the seeds of our destruction.

Nearly 66% of human pathogens and almost 75% of emerging or re-emerging human diseases (new diseases or diseases affecting naïve populations) are zoonotic (transmitted to humans from animals). This list includes some extremely nasty pathogens, like SARS, avian flu, and rabies. The rapid rise of zoonoses is the result of a number of anthropogenic (human-caused) factors, ranging from deforestation and urbanization to the increasing complexity and intensity of our food systems1.

Keep your friends close

There have been two revolutions in livestock management in recent history1. In the 19th century, European populations were booming, society was urbanizing at an unprecedented rate, and the demand for meat skyrocketed. To increase supply, farmers industrialized animal husbandry, packing thousands of animals into high throughput facilities and replacing forage with nutrient dense artificial feeds1,4. This trend continued throughout the 20th century, leading to the second revolution: the explosion of pig and poultry farming in the 1980s1.

Globally, pig and poultry production remain the fastest growing sectors of industrialized agriculture, growing 2.6 and 3.7%, respectively, over the last decade. In 2005 alone, 25 million pigs were traded internationally, which amounts to more than 2 million per month. Poultry production has also intensified. In the US, chickens and turkeys are raised in houses containing 15,000-70,000 animals. Industrialized agriculture depends on this kind of confined housing, as well as rapid turnover of livestock at the same site, and huge populations of closely related animals4. From a public health standpoint, this is a recipe for disaster. Aside from ethical concerns about keeping thinking, feeling beings in these conditions2, industrialized farms are ideal incubators for disease.

Too close for comfort.

And your enemies closer

Most zoonoses of concern are passed to humans from animals raised for consumption. Livestock herds cultivate disease in two ways. First, by providing a bridge between wild animal populations and humans. (This happens with with Nipah virus, which comes from bats, passes through domesticated pigs, and is transmitted to humans.) Second, by being the site of pathogen evolution themselves4, creating “production diseases”3. The close quarters and high turnover in industrialized agriculture can result in rapid pathogen replication, which increases the likelihood of mutation, possibly making the disease capable of infecting humans. While there are measures in place to prevent the spread of disease, the structure and design of industrial agriculture makes containment extremely challenging. Pathogens have been shown to move readily on farms, both between animals and spilling over into their human caretakers4. Workers are often unable to decontaminate themselves, and vets, farmers, livestock handlers, and slaughterhouse employees are all at higher risk for zoonoses3,4.

For zoonotic illnesses, the cure may be even worse than the disease. Zoonotic illnesses are considered huge public health risks, although they usually result in very few human deaths. Consequently, livestock are routinely treated with antibiotics to ward off sickness. This approach is a fearsome double-edged sword; it has successfully controlled diseases like tuberculosis and brucellosis, but it also encourages antibiotic resistance. By confronting bacteria with antibiotics, we are selecting for survivors (the bacteria that can withstand an antibacterial attack), and we may be creating a suite of untreatable superbugs3.

Once an outbreak occurs, herds are rarely treated; zoonotic epidemics are usually dealt with by culling livestock populations3,4, making the potential economic toll of these diseases enormous. The Dutch avian flu epidemic of 2003 led to the demise of 31 million birds, and amounted to hundreds of millions of euros in damages. There may also be cascading effects on farmers, who suffer the psychological impact of these losses, and of carrying out the slaughter of so many animals3.

For better or worse, industrialized agriculture has become a global phenomenon4, and its expansion and intensification seem inevitable in the face of the ever-increasing human population. While intensive agriculture has clear and substantial benefits, its risks are colossal. We may not be able to eradicate these practices, but we owe it to ourselves to better understand them. Our knowledge about intervention strategies against zoonoses is minimal, and it receives very little research funding. In the UK, a mere 1.6% of the funds allocated by the Medical Research Council were dedicated to health services or systems research in 20061. This must change– understanding may be the only thing that can save us from being consumed by our own appetite.


  1. Coker, R, J Rushton, S Mounier-Jack, E Karimuribo, P Lutumba, D Kambarage, DU Pfeiffer, K Stärk, & M Rweyemamu. (2011). Towards a conceptual framework to support one-health research for policy on emerging zoonoses. The Lancet, 11:326-331.
  1. Jochemsen, H. (2013). An ethical foundation for careful animal husbandry. Wageningen Journal of Life Sciences, 66:55-63.
  1. Kimman, T, M Hoek, MCM de Jong. (2013). Assessing and controlling health risks from animal husbandry. Wageningen Journal of Life Sciences, 66:7-14.
  1. Leibler, JH, J Otte, D Roland-Holst, DU Pfeiffer, RS Magalhaes, J Rushton, JP Graham, & EK Silbergeld. (2009). Industrial food animal production and global health risks: exploring the ecosystems and economics of avian influenza. EcoHealth, 6:58-70.

Image source: Creative Commons, http://en.wikipedia.org/wiki/Subtherapeutic_antibiotic_use_in_swine