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11 December 2019 | Story Leonie Bolleurs
Aids read more

According to Global Statistics, there were approximately 37,9 million people across the globe with HIV/Aids in 2018. They also state that in 2018, an estimated 1,7 million individuals worldwide became newly infected with HIV. 

In the city of Masvingo, Zimbabwe, Claris Shoko is a Statistics lecturer at the Great Zimbabwe University. In her PhD thesis at the University of the Free State (UFS) in the Department of Mathematical Statistics and Actuarial Sciences, she presented the argument that the inclusion of both the CD4 cell count and the viral-load counts in the monitoring and management of HIV+ patients on antiretroviral therapy (ART), is helping in reducing mortality rates, leading to improved life expectancy for HIV/Aids patients. 

She received her doctoral degree at the December UFS Graduation Ceremonies, with her thesis: Continuous-time Markov modelling of the effects of treatment regimens on HIV/Aids immunology and virology. 

CD4 cell count and viral-load count

Dr Shoko explains: “When the human immunodeficiency virus (HIV) enters the human body, the virus attacks the CD4 cells in their blood. This process damages CD4 cells, causing the number of white blood cells in the body to drop, making it difficult to fight infections.”

“Clinical markers such as CD4 cell count and viral-load count (number of HIV particles in a ml of blood) provide information about the progression of HIV/Aids in infected individuals. These markers fully define the immunology and the virology of HIV-infected individuals, thereby giving us a clear picture of how HIV/Aids evolve within an individual.”

Dr Shoko continues: “The development of highly active antiretroviral therapy (HAART) has helped substantially to reduce the death rate from HIV. HAART reduces viral load-count levels, blocking replication of HIV particles in the blood, resulting in an increase of CD4 cell counts and the life expectancy of individuals infected with HIV. This has made CD4 cell counts and viral-load counts the fundamental laboratory markers that are regularly used for patient management, in addition to predicting HIV/Aids disease progression or treatment outcomes.”

In the treatment of HIV/Aids, medical practitioners prescribe combination therapy to attack the virus at different stages of its life cycle, and medication to treat the opportunistic infections that may occur. “The introduction of combined antiretroviral therapy (cART) has led to the dramatic reduction in morbidity and mortality at both individual level and population level,” states Dr Shoko.

Once HIV-positive patients are put on cART, the effectiveness of treatment is monitored after the first three months and a further follow-up is done every six months thereafter. During the monitoring stages, CD4 cell count and viral load is measured. Patients are also screened for any tuberculosis (TB) co-infection and checked for any signs of drug resistance. These variables determine whether or not there is a need for treatment change. 

She continues: “Previous studies on HIV modelling could not include both CD4 cell count and viral load in one model, because of the collinearity between the two variables. In this study, the principal component approach for the treatment of collinearity between variables is used. Both variables were then included in one model, resulting in a better prediction of mortality than when only one of the variables is used.”

“Viral-load monitoring helps in checking for any possibilities of virologic failure or viral rebound, which increases the rate of mortality if not managed properly. CD4 cell count then comes in to monitor the potential development of opportunistic infections such as TB. TB is extremely fatal, but once detected and treated, the survival of HIV/Aids patients is assured,” Dr Shoko explains.

Markov model

She applied the Markov model in her study. The model, named after the Russian mathematician Andrey Markov, represents a general category of stochastic processes, characterised by six basic attributes: states, stages, actions, rewards, transitions, and constraints. 

According to Dr Shoko, Markov models assume that a patient is always in one of a finite number of discrete states, called Markov states. All events are modelled as transitions from one state to another. Each state is assigned a utility, and the contribution of this utility to the overall prognosis depends on the length of time spent in each state. For example, for a patient who is HIV positive, these states could be HIV+ (CD4 cell count above 200 cells/mm3), Aids (CD4 cell count below 200 cells/mm3) and Dead.

“Markov models are ideal for use in HIV/Aids studies, because they estimate the rate of transition between multiple-disease states while allowing for the possible reversibility of some states,” says Dr Shoko, quoting Hubbard and Zhou.

“Relatively fewer HIV modelling studies include a detailed description of the dynamics of HIV viral load count during stages of HIV disease progression. This could be due to the unavailability of data on viral load, particularly from low- and middle-income countries that have historically relied on monitoring CD4 cell counts for patients on ART because of higher costs of viral load-count testing,” Dr Shoko concludes

News Archive

Childhood obesity should be curbed early
2017-03-15

Description: Child obesity Tags: Child obesity

Serious intervention by parents is required to deal
with childhood obesity. Prof Louise van den Berg and
a group of final-year PhD students worked on a study
about the prevalence of obesity in six-year-olds in
South Africa.
Photo: Supplied

If your child is overweight when they start school at the age of six, unless you do something about it at that point, the indications are they are going to be overweight teenagers and obese adults. This is according to University of the Free State’s Prof Louise van den Berg.

Evidence has shown that overweight children and teenagers have a greater risk of developing lifestyle diseases such as type 2 diabetes, hypertension and cardiovascular disease later in life, and dying prematurely.

Obesity is a global pandemic rapidly spreading among adults and children, in developed and developing countries alike.

Dr Van den Berg worked with Keagan Di Ascenzo, Maryke Ferreira, Monja-Marie Kok, Anneke Lauwrens, all PhD students with the Department of Nutrition and Dietetics, to conduct the study. Their research found that children who are overweight by the time they turn six should be screened for weight problems.

Why six-year-olds?
Children who are overweight between the ages of two and five are five times more likely to be overweight when they are 12. There are two periods in a normal life cycle when the body makes new fat cells. The first is in the uterus and the second is around the age of six. The second phase lasts from the age of six to puberty.

The study assessed the prevalence of obesity in six-year-olds as part of a campaign in South Africa to raise awareness of the problem among parents and educators.

A total of 99 children were chosen from seven schools in Mangaung, the capital city of Free State. The schools were chosen from quintile four and five schools, which when measured by their own resources and economic circumstances, are well resourced and serve largely middle-class and wealthy communities.

The children’s weight, height and waist circumference were measured and used to calculate a body mass index score and waist-to-height ratio. Both these figures are good predictors for future lifestyle disease risks such as type 2 diabetes, hypertension and cardiovascular disease. A person with a good waist-to-height ratio can wrap a piece of string equal to their height around their waist at least twice.

When the children had a higher body mass index, they also had an increased waist to height ratio. The study found one in four children from the schools surveyed were overweight when they started primary school.

Nipping the fat in the bud
Although there are many factors that play a role in preventing childhood obesity, parents’ perceptions of their children’s weight play an important role. A recent study found that more than 50% of parents underestimate the weight of their obese children. These parents remain unaware of the risks their children face and are not motivated to take any action.

At least half of the parents whose children are overweight struggle to recognise their children’s weight problems fearing that they will be labelled or stigmatised. By the time they turn six overweight children should be referred to dieticians and nutritionists who are qualified to guide their parents in getting them to eat well and be more physically active at pre-primary and primary school.

The high prevalence of weight problems among six-year-olds found in this study is an urgent call to healthcare professionals to step up and empower parents, educators and children with the necessary skills for healthy dietary practices and adequate physical activity.

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