Meredith: Our brilliant team of Snapshot Serengeti undergraduate volunteers at the University of Minnesota are perhaps even more on top of the lion literature than I am! This week, we have a guest post from one such student, Clayton Mazur, describing some recent work of Dr. Packer’s on lion disease spread in Serengeti Park. This post is a synopsis of a scientific paper that can be accessed in full here. 

I propose we play a word-association game. I will offer a word and you think of what comes to mind. “Africa.” Did you imagine Mt. Kilimanjaro, or the towering, lush rain-forests of the Congo? “Wildlife.” Did you envision the sprawling savannas of Tanzania, home to hundreds of thousands of migrating wildebeest? If so, I would bet that your savanna also included the enigma of Africa: the African lion. Was he a graceful figure standing upon Pride Rock looking out over his kingdom? Perhaps he was laying in the shade, his dark mane flowing in the breeze as he waits for the females to return with a kill. I would argue that elegant images such as these are what come to mind for the majority the public. The portrayals of lions in the media- from Lion King to the MGM Lion- support this notion.  As elegant as these images are, reality is less than elegant for the lions living in Serengeti National Park in Tanzania, Africa.

African lions have unique social structures that help them brave the tough conditions of the savanna. Lions live in families called prides; one to two male lions rule a pride. The roles of female and male lions within a single pride are vastly different.  While females hunt, raise the cubs, and reproduce, male lions defend the pride from attack by other predators such as hyenas. Living in a large family group offers lions protection, but it also comes with costs. One cost is that females need to supply a large number of individuals with enough food for survival. Female lions coordinate hunts whereby they stalk prey and then give chase, but this technique only yields about 26% success. The low success rate forces large prides to split or starve.  Perhaps a more interesting difficulty of living in a large pride is the spread of disease within lion populations. As Dr. Craig Packer has found, disease prevalence is a threat to the current lion population.

A fatal disease that persists in the carnivores of Serengeti National Park is Canine Distemper Virus (CDV). CDV infects a range of carnivores, from dolphins to rodents and even some primates. The viral infection causes encephalitis, pneumonia, anorexia and eventually, death. You may be familiar with CDV if you own a dog, for many owners in the US vaccinate their dogs for CDV. In Serengeti National Park, where local villages cannot afford to vaccinate their dogs, CDV is a conservation concern for African Lions who contract CDV from domestic dogs. To try to remedy the concern, an intense vaccination regime started in 2003. Packer and colleagues attempted to characterize the progression of CDV in both domestic dogs and African Lions. Their goal was to determine if domestic dogs were responsible for the infections observed in African Lions. The team also wanted to determine if the 2003 vaccination program had any effect at reducing CDV in the domestic dogs and/or African Lions.

The scientists worked with blood plasma collected from both domestic dogs (obtained from 1992-2012) and from African lions (obtained from 1984-2012).  After collecting the blood samples, the team ran serological tests to detect for the presence of the CDV virus in individual dogs or lions. Using a Bayesian model, the scientists then calculated the probability that an individual lion or dog would contract CDV in one year. The scientists also used sensitivity models to determine the extent at which domestic dogs transmit CDV to lions. From the results of these models, the scientists were able to comment on the fate of the lions with regard to CDV.

The research team drew results by interpretation of the two models. They found that CDV had persisted in the populations of both dogs and lions for more than 25 years. Outbreaks of CDV occurred in 1981, possibly in 1976, and in 1993. Not only do these results suggest a historic presence of the fatal disease in the national park, the dynamics of each outbreak of the disease was unique. The scientists found that the year in which CDV infected the most dogs differed from the year in which CDV infected the most lions. The researchers proposed that this pattern identified domestic dogs as initial vectors for CDV in the park. After a 1994 outbreak in the lion population, the dynamics of the outbreaks become more disjoint. The disjointed dynamics between the domestic dog and lion populations suggest that after 1994, infections cycled through the dog population and the lion population separately. However, the spread of CDV between dogs and lions was not eliminated after 1994.

With domestic dogs established as an initial vector of CDV, the scientists wanted to know transmission rates between domestic dogs and lions. Again, they used a sensitivity model to predict this factor. The scientists found that domestic dogs were ten times more likely to spread CDV to lions than lions were to spread CDV to domestic dogs. With such a high prevalence of CDV in the domestic dog population and the tendency for CDV to spread from dog to lion, the effects of the 2003 vaccination effort were an important factor to analyze for the conservation of the Serengeti National Park lions. The scientists first analyzed the effects of the vaccine on the domestic dog population. Before 2003, there had been very sparse vaccination in villages surrounding Serengeti National Park. As was expected, this vaccination effort did little to curb CDV infection in either lions or domestic dogs. It was not until after 2003 when all villages to the east of Serengeti National Park and all villages within 10 km to the west of Serengeti National Park vaccinated their dogs against CDV did there exist a decrease (~5%) in CDV infections.

With CDV slightly decreased in domestic dogs due to the vaccination effort, was there a similar decrease in CDV infections in the lion populations?  Unfortunately, the sample size of lion serum that the scientists could obtain was not enough to comment on the updated magnitude of dog-lion CDV transmission. Overall, the scientists determined that CDV was still able to cycle in the lion population with very little reduction in the prevalence of the disease. However, not all is hopeless for the lion populations of Serengeti National Park. Dr. Packer’s team suggests that direct vaccination of lions may be more effective at preventing the disease. Additionally, the team suggests that advances in serological techniques would allow for increased accuracy when researching episodic diseases, such as CDV. Implementation of safe vaccines coupled with more accurate serological tests could minimize the effects of CDV outbreaks and ensure the health of the Serengeti lions.

As evident from the work of Dr. Packer and colleagues, there are threats to the conservation of the lion populations of Serengeti National Park. Not only do prides run the risk of individuals starving to death, splitting, and human-lion conflict, disease is another risk factor of living in a pride. Yet, these prides, these perfect families, come to mind when the public thinks about lions. Idealistic images of cubs play fighting or suckling from their mother are important for generating interest and compassion for African lions. One can be content with the image of the brave, courageous, elegant male lion standing on Pride Rock overlooking his kingdom, but one must simultaneously recognize the reality of the lion’s plight. Only then will conservation for lions be truly feasible.