Dr Samuel Kariuki is a Kenyan scientist who has been working for over fifteen years to understand salmonella, a disease that kills around 100,000 people in Africa each year. His research has focused particularly on children and previously little-understood patterns of the disease’s transmission.
On 31 October he was awarded the Royal Society Pfizer Award  and received a £60,000 grant towards a study that aims to better understand disease transmission patterns and develop a vaccine. Sam Kariuki is currently Chief Research Scientist and Head of Department at the Centre for Microbiology Research at the Kenya Medical Research Institute in Nairobi.
What was your early life like, and how did you get into medicine?
I would say my life started back in the villages of Kenya, when I was a youngster. During those early days it was very hard to know what you wanted to do. It was at the age of 17 that I started seriously thinking about a career in science. We had a doctor who was a recent graduate in our village, and he looked like he was enjoying life - but then again, I wasn’t very happy about working at night in hospitals!
I just chose veterinary medicine, because I wanted to understand the disease process in animals that were hurting humans as well. I actually never went out to practise - I went directly back to do a Masters course in Pharmacology to try and understand medicines and how they work.
What specifically attracted you to pharmacology?
I think I was fascinated by how medicines actually treat diseases. And this was mainly due to my inquisitive reading, particularly articles in the newspaper at that time about viruses becoming resistant to anti-viral treatment. I became very interested in knowing the basis of this. Was resistance the same in animals as in humans?
What did you find?
We found some very interesting data from our small project on salmonella. We found that the kind of resistance genes you found in animals were different from those you find in humans - ultimately the bugs we found in humans carry much more resistance. And we could trace this very directly to the fact that there is much more antibiotic use in humans, compared to what the farmers were using back home. There was a clear correlation between the misuse of antibiotics, and the emergence of antibiotic resistance.
Didn’t you later prove the possibility of human-to-human transmission of the salmonella virus, which was not previously thought possible?
Yes, actually that came much later on. That hypothesis actually came from our understanding of disease transmission dynamics during my PHD, where I decided to study Salmonella and E-coli. We used very crude methods, but we were able to show that strain types of salmonella and e-coli in animals were different then those in humans.
The significance of this was to challenge the dogma of what you call “zoonotic” bacteria – bugs that can transmit between humans and animals - having reserved status in people who get in contact with animals, or eat contaminated foods of animal origin. We conducted case control studies with patients in hospitals, isolated from the source of the disease – if it was a true “zoonotic” infection then we would have found same disease strand in these patients as well as in the animals. But that wasn’t the case.
That prompted me to think very critically. This hypothesis - that animals are the only sources of certain diseases like salmonella – might not be true. But when we put this hypothesis forward to journals in the year 2006, my first publication was rejected by six journals.
What were the effect of salmonella in Kenya and the surrounding area when you began your work? Did it feel like an immediate threat?
Some of my colleagues in the area had noticed in the 80s – through clinical audit – that salmonella typhimurium in particular was causing very severe blood borne infections, and was caused a disproportionately high caseload over time. And the mortality rate was quite high. Some of the infected children came down with meningitis, which was quite unusual. In these children almost half of them died - in those with blood born infections, 20-30 percent would die within 48 hours if they were not treated. By the year 2007 we were able to show that the strain type found in children in Kenya, and in 10 surrounding African countries, has evolved in the past 35 years. It has become host adapted.
What was the relationship between the HIV epidemic and salmonella? Were they closely linked?
No doubt. The salmonella epidemic is very closely linked to any immunosuppressive condition, including HIV. As you know, in the early 80s HIV had just gone into Africa and it was fast spreading. But before that my colleagues had observed that Salmonella was causing particularly high rates of infection in the paediatric wards with children who had HIV, or had immunosuppression due to malnutrition. It was particularly prominent as well in adults with HIV – about 60 percent were co-infected.
Do you feel like you are making a difference?
I think so - one of my joys of doing research is being able to understand how we can prevent and control disease. Sometimes it is difficult if you are dealing with a sceptical audience, especially if it is something new. But I think if somebody persists, you are able to see that whatever you are doing, in a small way, is helping to save lives. Even if you are able to save one life, it is very satisfying. That in itself makes me feel that science is contributing towards alleviating suffering.
Would you say disease prevention is fundamental to a healthy society? Can a country develop if its people are not well?
I think in any country, the health of its citizens is the number one investment in terms of economic development. If there is a sick nation, it will never develop in an economic sense. In terms of the national outlook, I think governments must invest much more in ensuring that disease is controlled and treated, to invest in proper diagnosis in hospitals, and to put more resources in disease hotspots.
You work with something that is continually changing its shape –shifting and evolving as soon as you come to understand it. Do you ever feel like you are fighting a losing battle?
It’s a very good question. The bugs are very clever. They are probably much cleverer than man, and we tend to underestimate their capability. We have been fighting this battle for all time. If you remember in the early days when penicillin was discovered, we seemed to think we were going to cure everything. But of course not! Because the bugs are much cleverer than us. We can have our hypothesis, but the bugs might be thinking differently, and that calls for vigilance, for understanding of a disease over time and over space, so we don’t lose track of what is going on.
What piece of technology in recent times would you say has had the greatest impact on disease research?
In my opinion, the greatest technology that has come to our rescue – both in understand disease and understanding ourselves – is whole genome sequencing. It has helped us understand our own selves in terms of genomics, to understand the human chromosome, disease susceptibility - something we didn’t even know five years ago. Whole genome sequencing has made us understand the human host.
What single thing would help most with disease research in the future?
I’ll speak from the developing world’s points of view – I think one of the greatest challenges we face is that we do not have adequately trained manpower. I feel the biggest need is increasing capacity. In this I mean being able to train more young people to adapt these technologies to better use, to disease prevention and control in an African context. It is a great challenge.
Do you believe it is possible to live in a disease free world? Is that even the goal of science, or are we more realistic than that?
I think nature, in itself, abhors vacuums. I think it is very unlikely that we will be unable to control all diseases at some stage in the future. But what I do know is that we can control situations to control diseases.
The challenge is the fact that sometimes we concentrate so much on diseases that have been popular, that have been well known for a long time – like malaria, or TB, or HIV – and forget that these are the same populations that are being effected by other diseases like salmonella and typhoid.
I was wondering about that. Is it more frustrating to work with a less “popular” illness?
Indeed. The really high profile diseases are very politically supported. So it is easier to mobilize resources, nationally and internationally. To a degree that has helped maintain control of those diseases. Malaria, for example, has had cases reduced by 60 percent. And that in itself is good! But what we need to keep in mind is that these are the same populations affected by other, neglected diseases.
So you would say salmonella is a “neglected” disease?
Well it hasn’t been classified as a neglected disease, but personally I would like to put it in the bracket. We don’t put enough resources into management, diagnosis and control of this disease, because, politically, it is not well known.
Is there anything you would like to forget?
I think I would like to forget instances when we were turned down by reviewers, because we challenged the dogma. Those were depressing times. There were times when you wake up and think, do I go on with this science? Or do I just go into business and make some money?
Was there a plan?
I think, scientifically, you move forward with a plan. Plans are driven by what you find today - to a large extent they dictate what you do tomorrow. Fascination is driven by being inquisitive. And you become inquisitive because you want to look for solutions. That in itself is what keeps one going.
Are we all doomed?
I wouldn’t say so. As I say, the bugs are very clever! But I think we have developed the technology, and are sharpening the technology to understand these bugs much better. And once we understand them, we will probably be able to come up with tools to know their tricks, and avoid being tricked by them again.
1963 – Born Londiani, in the Rift Valley of Kenya
1989 – M.Sc. in Pharmacology and Toxicology at Oslo University
1991 – Works with Kenya Medical Research Institute and a team from Oxford University studying HIV/AIDS epidemic at its peak in Africa
1994 - PhD in Antimicrobial resistance and epidemiology of Salmonella in Kenya
1997-2006 – Wins two fellowships from the Wellcome Trust to study salmonella infection in children and the transmission dynamics of the illness
2012 – Wins Royal Soceity Pfizer Award for salmonella research