Natural Sciences
Emergence of a Viral Disease Epidemic of Sweet potato in Eastern Africa is Imminent – Plant virologists warn
When COVID-19 emerged in 2019, it first remained temporarily localized as an epidemic in Huan China until it broke Chinese national and Asian continental borders attaining a global pandemic status. With COVID-19 and other epidemics and/or pandemics of humans and livestock, it is easier to explain the obvious impact on humans and/or livestock.
What about virus epidemics and pandemics that affect plants?
Virus epidemics and pandemics that affect plants cause significant disruptions in food production. In fact, the emergence and re-emergence of extremely dangerous plant viruses is the major pain to the 21st century agriculture and sustainable food production.
Viral diseases of plants lead to complex outcomes of food shortages, economic meltdown and loss of lives especially when the affected crop plants are central to the economics and livelihoods of the people. Think of what would happen if an epidemic caused significant effect or eliminated crops like maize, banana, cassava or sweetpotato from sub-Saharan Africa.
Most viruses affecting livestock and humans are spread and transmitted by means of physical contact between hosts. Furthermore, human and livestock hosts are mobile. On the other hand, plants do not move and must thus depend on other agents (vectors) for the spread of viruses between hosts. Consequently, over 98% of plant viruses are transmitted by vectors. These vectors may include arthropods (especially insects), nematodes, fungi, and parasitic plants. In plants, a virus disease epidemic becomes optimized by the ability of vectors facilitating fast spread of the virus in an agro-ecosystem.
New study predicts emergence of disease epidemic in sweetpotato
A new study led by Prof. Arthur Tugume at the Department of Plant Sciences, Microbiology and Biotechnology in the College of Natural Sciences at Makerere University predicts potential of emergence of a new disease epidemic in sweetpotato.
The study recognizes that by default, viruses are not constrained to perpetually occupy a single ecological niche. This is because viruses have inherent genetic and evolutionary abilities that enable their acquisition of better fitness to always expand their host and geographical ranges.
While viruses enjoy such fitness advantages in nature, the current study points out unique examples where some viruses in eastern Africa behave awkwardly. These viruses first hid under the guise of being less important and seemingly of no impact in cropping systems, and all of a sudden hell broke loose and the entire farming system was caught unaware.
The study titled; “Endemism and reemergence potential of the ipomovirus Sweetpotato mild mottle virus (family Potyviridae) in Eastern Africa: half a century of mystery” shows that a virus, named Sweetpotato mild mottle virus (SPMMV) was first detected in eastern Africa in the 1970’s. SPMMV is currently the third most prevalent virus of sweepotato in the region and is most destructive in mixed infections with other viruses. Very strangely, SPMMV is geographically restricted to eastern Africa (confirmed only in Uganda, Kenya and Tanzania). This sharply contradicts other known sweetpotato viruses that occur globally wherever sweetpotato is grown.
According to Dr. Deusdedith Mbanzibwa a co-author and Head of Disease Control Unit at Tanzanian Agricultural Research Institute, “it is a half-century-old mystery how SPMMV remains localized in East Africa while other viruses on sweetpotato show a global incidence.” Dr. Mbanzibwa adds, “it is important we generate basic information on this virus as soon as possible such that immediately an epidemic explodes we can counter-it based on the information we have as opposed to being caught unaware of the destructive effects of an epidemic.”
Why should we be concerned about outbreak of an epidemic on sweetpotato?
Plant disease epidemics cause a breakdown in food production and availability in communities that depend on the affected plants as food staples. If sweetpotato production breaks down, it directly translates into limited food supplies in local communities that depend on it for food.
According to Dr. Titus Alicai, a senior virologist and co-author based at the National Crops Resources Research Institute (NaCRRI), Namulonge Uganda, “between the 1980’s-1990’s, a devastating viral pandemic (cassava mosaic disease, CMD) destroyed cassava cropping systems in eastern Africa. As a result, dozens of lives were lost because many communities solely depended on cassava for food and income”. Although these viruses had been detected in the region as early as 1800’s, it was not until the 1980s that destructive effects of the disease became apparent.
Dr. Alicai adds that, “when cassava got destroyed by CMD, sweetpotato became an immediate alternative to millions of hungry people, but now sweetpotato is also burdened with diseases arising from viruses.” Despite heavy investments in disease control in cassava, the CMD pandemic is not completely controlled.
Why is eastern Africa important with respect to emergence of plant viruses?
According to this study, SPMMV is not the first unique virus to emerge or reemerge in eastern Africa. An earlier study by Prof. Tugume and colleagues published in 2010 in Molecular Ecology showed that East Africa is a hotspot for the evolutionary diversification of yet another virus in sweetpotato, named Sweetpotato feathery mottle virus (SPFMV).
Many studies show this region as the home of epidemics in rice caused by Rice yellow mottle virus (RYMV). Highly lethal strains of Cassava mosaic geminiviruses (CMGs) causing CMD initiated this epidemic from eastern Africa. Unique strains of Sweetpotato chlorotic stunt virus (SPCSV) are incident in eastern Africa. SPCSV is unique because it almost indiscriminately enhances the viral concentrations of other co-infecting viruses in sweetpotato. The list of damaging plant viruses or their strains that have emerged from eastern African region is long and cannot not be exhausted here.
Biologists studying diversity of plants and animals have also coded eastern Africa as a home of the “hottest hotspot of biodiversity” of endemic land plants and animals located in Eastern Arc Mountains of Kenya and Tanzania. The features of eastern African ecosystem that incite virus epidemics in plants are not fully known. However, it is suspected that the microclimatic changes as modulated by the Indian Ocean dipole could be one of the drivers of virus emergence and reemergence in the region.
Emergence of SPMMV in sweetpotato closely resemble that of viruses in cassava
The current study specifically compared SPMMV with two viruses infecting cassava: cassava brown streak virus, and Ugandan cassava brown streak virus, collectively called cassava brown streak ipomoviruses (CBSIs).
CBSIs first appeared in the 1930’s in coastal east Africa but went completely silent for about 70 years and then suddenly re-emerged in late 1990’s-mid 2000’s to what is today the single largest threat to cassava production in Africa. CBSIs cause a disease called “cassava brown streak disease” (CBSD). Between 1930’s-1990’s, the CBSIs were able to “amass ability” to cause untold suffering of cassava cropping from 2000’s to-date.
Similarly, since the 1970’s when SPMMV was first reported in the region, the virus has been “amassing an ability” to cause more disease in sweetpotato. This is implied directly by evidence of positive selection found in its genes. Positive selection refers to “survival for the fittest” in Charles Darwin’s terms to mean that, individual virus particles in the SPMMV population are becoming more and more highly efficient in causing disease. Today, half a century later, one can argue that it is about time that the SPMMV will incite a new disease.
Note that both SPMMV and CBSIs belong to the same taxonomic grouping of plant viruses in a genus called “Ipomovirus”, and family called “Potyviridae” which is the largest family of plant viruses with RNA genomes. Hence, similarities in the disease spread between SPMMV and CBSIs are not unexpected.
Expert guide to sweetpotato virology research for preparations against the epidemic
“If we can generate advance basic scientific information concerning how the SPMMV infects sweetpotato plants, how it is transmitted by vectors between plants, and circumstances fostering field spread of the virus, we will be better prepared to handle an epidemic that may arise from the virus,” Prof. Tugume states.
He adds: “we should be able to undertake these studies quickly because SPMMV is naturally incident on sweetpotatoes in Uganda, Kenya and Tanzania in levels causing less damage on its own at the moment, although this damage escalates when the virus occurs in multiple infections.”
The co-authors highlight serious research gaps for critical research investment in sweetpotato virology. Vector transmission is such an important aspect of virus disease epidemics of plants. Therefore, this study has proposed three possible explanations to account for the virus-vector and virus-host relationships of SPMMV. These are called hypothesis #1, #2, and #3, built in a fashion that allows experimentation to prove them right or wrong:
- Hypothesis #1: “SPMMV is opportunistically aphid-transmitted with potyvirus SPFMV as a helper virus.” This hypothesis postulates that SPMMV is transmitted by “chance” by a group of insects called aphids but this happens when SPMMV co-infects sweetpotatoes with another virus, SPFMV that is transmitted efficiently by aphids.
- Hypothesis #2: “Vector-mediated transmission of SPMMV is modulated by synergism with SPCSV.” Under this hypothesis, the concentrations of SPMMV in plant tissues increases when it co-infects with another virus, SPCSV, and this increases chances of SPMMV being picked by insects for transmission to other plants.
- Hypothesis #3: “SPMMV tropism and histo-localization changes upon co-infection with SPCSV.” How much viral concentration is found in different plant tissues can change depending on which tissues that are preferred by the virus. Certain plant viruses prefer to stay and multiply from certain tissues than others.
Dr. Alicai said, “If we can determine vector transmission dynamics including the actual vector(s) transmitting SPMMV, which plant tissues the virus prefers for its multiplication, and generate many complete sequences of SPMMV genomes, we will be better prepared for epidemics arising from the emergence of SPMMV”.
Sweetpotato is a vegetatively propagated plant in which the top-most 15-40cm part of the plant is used for initiating the new crop, a practice that is the main route of accelerated of virus spread in the cropping system. Also, insects especially aphids and whiteflies are the major vectors transmitting viruses in sweetpotato. The research gaps highlighted with respect to SPMMV require urgent attention for advance preparation in case an epidemic breaks loose on the sweetpotato cropping system.
This study has been published by the American Phytopathological Society (APS) in an open access journal, “Phytobiomes Journal”, and is freely accessible on https://apsjournals.apsnet.org/doi/10.1094/PBIOMES-05-22-0031-RVW
For more details, please contact;
Prof. Arthur Tugume
Lead Scientist
Department of Plant Sciences, Microbiology and Biotechnology
College of Natural Sciences (CoNAS)
Makerere University
Email: arthur.tugume@mak.ac.ug
Tel: +256772514841
Dr. Deusdedith Mbanzibwa
Tanzania Agricultural Research Institute (TARI),
Biosciences Centre, Dodoma, Tanzania
Email: d.mbanzibwa@yahoo.co.uk
Email: Tel: +255755881758
Dr. Titus Alicai
Root Crops Research Program
National Crops Resources Research Institute (NaCRRI)
National Agricultural Research Organization (NARO)
Email: talicai@hotmail.com
Tel: +256772970585
Hasifa Kabejja
Principal Communication Officer
College of Natural Sciences
Makerere University
Email: pr.cns@mak.ac.ug
Tel: +256774904211
Natural Sciences
Change of Guard: Prof. Michael Owor Hands Over Office of Dean, School of Physical Sciences to Prof. David Ssevviiri
Prof. Michael Owor has officially handed over the office of Dean, School of Physical Sciences to Prof. David Ssevviiri. Prof. Owor has served as Dean since 1st February 2022. Following his appointment by the University Council, Prof. Ssevviiri will serve as Dean for the next four years, effective 6th May 2026.
Handover Ceremony
Held on 28th May 2026 in the office of the Dean, the handover ceremony was overseen by Makerere University Chief of Internal Audit, Mr. Patrick Akonyet. It was attended by the Deputy Principal of the College of Natural Sciences (CoNAS), Prof. Juma Kasozi; the Head of the Department of Chemistry, Dr Emmanuel Tebandeke; the representative of the Head of the Department of Physics, Dr. Nicholas Kwarikunda; the representative of the Head of the Department of Geology and Petroleum Studies, Dr Denis Mutebi; the College Human Resource Officer, Ms. Kevin Nabiryo Mikwano; and the College and School Registrars.
Remarks from the College leadership
On behalf of the College leadership, Prof. Juma Kasozi commended Prof. Owor for his dedicated service and leadership throughout his tenure and congratulated Prof. Ssevviiri upon his appointment, wishing him success in his new role.
Achievements and remarks by the outgoing Dean
During his tenure, Prof. Owor chaired the School Academic Board and several key committees, including the Establishment and Appointments Committee, the Examination Malpractices Committee, and the Irregularities and Appeals Committee. He also presided over MSc viva voce examinations and PhD public defenses. Under his leadership, he ensured the timely submission of results, eliminated academic backlogs, and strengthened the coordination of graduate examinations, while also supporting the development and review of academic programmes. He has also served as the Patron of the CoNAS Students’ Guild.
In his remarks, Prof. Owor expressed gratitude to the University Council and Management for the opportunity accorded to him to serve as Dean. He also thanked the College leadership and staff for their support and reaffirmed his commitment to continue serving the University.
“I want to thank the University Management through the Chief Human Resource Officer for appointing me as dean, School of Physical Sciences for the last four years. I pledge my total support to the incoming Dean of the School. I also pledge to continue offering my services to the University through my mother Department, Geology and Petroleum Studies.”
Remarks from the Directorate of Human Resources
Representing the Directorate of Human Resources (DHR), Ms. Kevin Nabiryo Mikwano commended Prof. Owor for his leadership and contributions during his tenure.
“You have steered the school through curriculum reforms, staff development, student growth, and your commitment to both staff and students has not gone unnoticed. The foundation you have laid will continue to support the school’s progress. Thank you for your partnership with the Directorate of Human Resources in ensuring staff welfare, recruitment, and performance processes were handled with integrity and care.”
She also congratulated Prof. Ssevviiri on his appointment, expressing confidence in his leadership and vision. She reaffirmed the Directorate’s readiness to support him in team building, talent management, and fostering a positive working environment for academic, administrative, and support staff. She further encouraged staff to maintain strong collaboration with the incoming Dean, emphasizing: “The success of the school depends on how well we work together. At the DHR, our commitment is to ensure that policies, processes, and people management practices support the school’s academic mission. May this handover mark the beginning of another strong chapter for the School of Physical Sciences.”
Guidance on the officially recognized Government handover procedure
The Chief of Internal Audit, Mr. Patrick Akonyet, commended both the outgoing and incoming Deans and emphasized adherence to the Government of Uganda handover and taking of office procedures. He noted that strict compliance with established guidelines is essential for accountability, transparency, institutional continuity, and smooth transition of responsibilities.
Remarks by the incoming Dean
In his remarks, Prof. David Ssevviiri thanked Prof. Owor for his service and appreciated the University Management for his appointment. He emphasized the importance of the School of Physical Sciences in advancing science and innovation. “We have a responsibility of nurturing our students into innovative problem solvers. The future of Science depends on how well we prepare our students. Building on the successes of my predecessors, and working collaboratively through our Departments, we can further contribute to solving real world challenges.
Profile of Prof. David Ssevviiri
Prof. David Ssevviiri is a Ugandan mathematician and academic leader serving as an Associate Professor of Mathematics at Makerere University, College of Natural Sciences. He is widely recognized for his work in pure mathematics, particularly in algebra, module theory, ring theory, algebraic geometry, and local cohomology.
He holds a Bachelor of Science with Education in Mathematics and Chemistry from Makerere University, as well as a Master of Science in Mathematics from the same institution. He also obtained an additional MSc and a PhD in Mathematics from Nelson Mandela Metropolitan University (now Nelson Mandela University), South Africa. His doctoral research, A Contribution to the Theory of Prime Modules, focused on advanced module theory and algebra.
Prof. Ssevviiri joined Makerere University in 2011 as an Assistant Lecturer and rose to the rank of Associate Professor in 2022. He previously served as Head of the Department of Mathematics from 2015 to 2020, where he contributed to strengthening teaching, research collaboration, and postgraduate training.
His research interests include primeness and nilpotency in ring and module theory, torsion theory, radical theory, homological algebra, and the interaction between algebra and algebraic geometry. He has authored and co-authored several peer-reviewed publications in international journals, contributing significantly to advancements in abstract algebra.
Beyond teaching and research, he has contributed to mathematics development in East Africa through student supervision, external examining, and coordination of regional academic programs. He has also participated in initiatives aimed at promoting mathematics education and encouraging young people to pursue careers in science and technology.
Pictorial of the ceremony: https://drive.google.com/drive/folders/1pmWX5H46UHbFkTT-I4OIJwFbXIwuO6e1?usp=sharing
A team of researchers from Makerere University has presented findings of a study on the persistent poor performance in Biology in national examinations to senior officials at the Ministry of Education and Sports.
The findings were shared during a dissemination meeting attended by the Ministry’s top management, led by Permanent Secretary Kedrace Turyagenda.
The study, commissioned by the Ministry in 2023, was conducted by researchers from the College of Natural Sciences (CoNAS) and the College of Education and External Studies (CEES). It was spearheaded by Prof. Fredrick Muyodi as Principal Investigator, alongside Assoc. Prof. Josephine Esaete (Co-Principal Investigator) and Prof. Arthur Tugume among others.
Titled “Examining the Factors Accounting for Poor Academic Performance in Biology in Uganda’s National Examinations,” the study covered all regions of the country, engaging more than 5,200 respondents across 100 districts through surveys, interviews, and observations.
Key findings
The research identified limited field-based learning and poor digital access as the most critical and consistent challenges affecting both Ordinary and Advanced Level students across all regions.
At Advanced Level, the lack of project-based learning was also cited as a significant constraint. Learners reported limited engagement with Biology beyond the classroom, a factor that weakens conceptual understanding and application in examinations.
The study further highlighted the role of community attitudes and perceptions in shaping student performance in the subject.
Recommendations
The researchers recommended increased investment in field-based learning, including field trips and project work, as well as expansion of digital infrastructure to improve access to learning resources.
Other proposed measures include strengthening school laboratory facilities, enhancing teacher capacity through continuous professional development, promoting student engagement through academic clubs and mentorship programmes, and fostering stronger family and community support for science education.
Next steps
The research team is seeking funding to pilot targeted interventions, particularly in regions most affected by the challenges identified, and to develop a monitoring and evaluation framework to guide implementation.
The findings are expected to inform policy and interventions aimed at improving Biology performance and strengthening science education in Uganda.
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