Following in the Footsteps of COVID-19 for the Cocoa Swollen Shoot Virus: Contact Tracing, Testing, and Treatment

Five months after the first lock downs due to the COVID-19 pandemic, one key lesson learned is that aggressive contact tracing, testing, treatment, and physical distancing has shown good results in reducing transmission of the virus. Africa is no exception with a mostly effective and comprehensive approach. Campaigns on social distancing, personal hygiene and cleaning, and mask wearing are being deployed. So far, these campaigns have contributed to reducing the spread of the virus in many African countries.

As everyone around the world is learning about viruses and how to control their spread, the cocoa sector continues to gain a better understanding of the cocoa swollen shoot virus disease, or CSSVD. CSSVD has been killing cocoa trees in West Africa since 1936, forcing farmers to abandon land that has become unsuitable and to face poverty. As farmers then look for new sources of income, they may resort to deforestation or rural flight. Despite this major impact on farmers’ livelihoods, this problem has received too little attention.

Like COVID-19, CSSVD can be a silent killer: trees get infected by mealybugs and can be asymptomatic at first while spreading the virus to surrounding trees. Côte d’Ivoire and Ghana, the largest cocoa producing countries, have cut down millions of infected trees but they have never been able to contain the rapid spread of the virus. In 2017, CSSVD infected 16% of Ghana’s cocoa farms. Today, Ghana Cocoa Board (COCOBOD) estimates that 23% of the country’s 1.9 million hectares of planted cocoa is infected by the virus. If nothing is done, the spread will continue.

We’re learning from the COVID-19 crisis that we should take a more aggressive ‘3T’ strategy of tracing, testing, and treatment of all infected farms.

Tracing COVID-19 is a labor-intensive activity that consists in alerting all those who have been in close contact with an infected person. For CSSVD, tracing will mean identifying all potentially infected trees/farms based on visual symptoms. These may include:

1. leaf discoloration,
2. red veins on young leaves, and
3. stem and root swelling and tree dieback.

A quick identification of an infected tree/farm is critical to stop the spread of the disease. Once a tree/farm is identified as potentially infected, all nearby cocoa trees or farms should be monitored and assessed for CSSVD as well. So far, such systematic tracing is not available for CSSVD and it could be worth empowering farmers or youth in cocoa farming communities to monitor cocoa trees and farms.

When a tree/farm is declared potentially infected, the farm should be reported for testing, together with all neighboring farms. Rapid testing should be followed by interviews with the farmer and all workers in the farm (if any) to trace other farms they have visited within the last month. Like for COVID-19, testing for CSSVD is based on a DNA test using polymerase chain reaction (PCR) to detect the DNA of the virus in the cocoa tree. The World Cocoa Foundation will soon deploy a laboratory-based early testing DNA tool against CSSVD in West Africa. The tool will be used to test all potentially infected trees/farms before symptoms appear. The lab-based tool will be complemented by a hand-held tool for rapid field diagnosis. WCF hopes that widespread use of these tools will soon become a reality.

Treatment is the last mile of the 3T strategy. However, there is no fool proof treatment against CSSVD. All treatments against the mealybugs responsible for carrying the virus have failed, no vaccine is available, and no tolerant cocoa varieties exist. In 2018, Ghana and Côte d’Ivoire – the two most affected countries – agreed with the Abidjan Declaration to collaborate to eradicate the virus and recommended cutting and destroying all trees in an infected farm. Since 1960, this approach has been implemented with no success.

The best strategy for now is to cut down all cocoa trees of an infected farm and replant after one or two years with improved cocoa varieties in association with shade agroforestry trees. Barrier crops can help isolate the farm and trap mealybugs, creating a kind of “social distance” between farms.

Eradication of CSSVD will require having a system thinking and transdisciplinary approach on tracing, testing, and treatment. This would include putting in place a facility responsible for treatment. At this time, this responsibility is not clearly established. The facility should be staffed with plant virologists, molecular biologists, plant breeders, plant entomologists, system agronomists, and researchers to develop and deploy treatment protocols when a tree or a farm tests positive. And, hopefully, these scientists could collaborate with other third parties to put an end to CSSVD by breeding tolerant and resistant cocoa plant varieties.