Previous TB work

“In 1993, my first year at the KMP farm, I had spent countless mornings at the Kakoo group’s burrows, working to habituate them to human presence, when the group suddenly started to dwindle. One by one the animals disappeared, some of them showing signs of a disease, until the entire group was lost. A year’s worth of habituation efforts was all in vain. Luckily, my colleagues were luckier with their groups. But looking back now, Kakoo probably was the first group in the KMP history that was lost to tuberculosis; TB has always been there.” says Marta Manser.

The disease remained present in the KMP meerkat population, but it wasn’t until 2000 that it was first diagnosed as tuberculosis (TB): A young wild immigrant male, VXM005, seemed to have brought it into the X-Iles group in late 1998. He was last seen in March 1999, but by July the dominant female VLF005 and three more X-Iles males had developed symptoms of this mysterious disease. Their disease was eventually identified as tuberculosis. Since then, the count of meerkat groups fully or partly extinguished by TB has exceeded 20; over 200 animals succumbed to the disease. The following chapters look back on the research about meerkat TB done at the KMP in the past.

 

Early findings (1993 to 2007)

Based on own observations and research on TB in other species, the KMP researchers learned to consider the following as symptoms of a TB infection in meerkats:

• Lumps (lymph node swellings) usually in the neck/head region, but also in other parts of the body; in many cases the lumps burst open in the last stages of the disease.
• Dramatic weight loss in short time
• Lethargy over a longer period

Preliminary analyses of life history data showed that:

• TB infections are not correlated with gender or age.
• There is no recovery once a meerkat expresses clear (open) lumps.

There were several options on how to deal with the disease:

• Treatment with antibiotics: This was no option once it became clear that the disease was TB. TB is extremely difficult to treat and heal; it requires the (human) patient to be treated over the course of several months with a very tight schedule of medications. This would only be feasible in a cage, for meerkats, and it was never an option to cage a potentially large number of meerkats for a long time, with unclear outcome.
• Vaccination: It has been a theoretical option for a long time to vaccinate the meerkats against TB, but lack of proven methods and of knowledge about how the disease spreads led the researchers to postpone vaccinations.
• Euthanisation: The last option to possibly prevent an uncontrolled spread of TB in the meerkat population was to euthanise meerkats with TB symptoms, to keep  them from passing on the bacilli. With the other options not feasible, euthanisation became the method of choice. Until now, roughly 3/4 of the meerkats with TB symptoms were euthanised, whereas 1/4 disappeared before this could happen.

 

Work by Julian Drewe and Coworkers (2005 to 2009)

With TB becoming an important problem in the population, the KMP decided to study it in more detail. The focus of the ensuing PhD study by veterinary surgeon Julian Drewe was to better characterise TB symptoms, to trial a variety of tests to try to diagnose TB in meerkats before the typical symptoms appear, and to understand how the disease is transmitted between individuals and groups of meerkats (its epidemiology). These studies are summarised below. In addition, Julian also published work on social interactions of meerkats. This work serves as the basis for studies on how TB is transferred within the population.

J. Comp. Path. (2009), Vol. 140, 12-24
Pathology of Mycobacterium bovis Infection in Wild Meerkats (Suricata suricatta)
J. A. Drewe, A. K. Foote, R. L. Sutcliffe and G. P. Pearce

Based on the post-mortem analysis of 52 individuals, the study suggests that the larger part of infections occur via the respiratory tract (inhalation of droplets containing tuberculosis bacilli), but infection via the digestive path (food/milk/grooming) or skin (biting) may also occur. Once an organ is infected, the infection can spread rapidly, via the blood, or via the lymph in late stages. The bacilli leave the body again via the respiration tract (sneezing) or from infected skin wounds. Transmission via faeces and urine seems less common, judging from the fact that the respective organs are less infected. So the transmission – which in other species usually needs repeat exposure to the bacilli – could be during grooming and other social activities or during fighting/biting.

J Vet Diagn Invest (2009), 21: 31–39
Accuracy of three diagnostic tests for determining Mycobacterium bovis infection status in live-sampled wild meerkats (Suricata suricatta)
Julian A. Drewe, Gillian S. Dean, Anita L. Michel, Gareth P. Pearce

With the TB symptoms not always clear and unambiguous, the KMP needed means to find out which individual was a TB carrier – the sooner after infection the better. This study tried to establish a reliable test for TB that could be used in the field. Three tests were compared: MAPIA and RT (two recently developed tests based on blood samples) with bacterial cultures of tracheal washes (a traditional, but complicated, lengthy test), in samples of 240 meerkats. The study showed that a combination of the two new tests gave the most accurate result.

Proceedings of the Royal Society B (2010), 277: 633–642
Who infects whom? Social networks and tuberculosis transmission in wild meerkats
Julian A. Drewe
Transmission of TB is strongly influenced by who contacts whom. This paper brings together the results of diagnostic tests performed from 2005 to 2008 with the Kalahari Meerkat Project’s records of social interactions between individuals and groups of meerkats. The relative importance of a range of social interactions (such as grooming, IGIs and aggressive evictions) in spreading disease between meerkats was examined. Contrary to predictions, the most socially interactive animals (the dominant females) were found not to be at highest risk of acquiring infection, indicating that in addition to contact frequency, the type and direction of interactions must be considered when quantifying disease risk.

The three publications can be downloaded here:
Pathology – Diagnostics – Transmission
Please note that the Pathology publication contains pictures of post-mortem sections that may not be suitable for kids or other sensitive persons.

 

Recent findings (since 2009)

TB research resumed only recently. This work includes studies to the nature of the TB bacillus involved in meerkat TB. It currently seems that the bacillus strain responsible for meerkat TB is neither bovine nor human TB but rather a type of TB adapted to the meerkat.