Unanticipated events and the need for long-term studies
In 1994, a terrible disease ripped through the Serengeti, killing lion after lion. By the end of the year, a third of the lions in the Serengeti were dead. The culprit was a virus known as canine distemper, and lions that died of the disease did not die quietly. The symptoms were clear to any observer: facial twitching, disorientation, and eventually convulsive seizures.
The lions in Craig’s study area were not spared, but the data he had been collecting over the previous decades proved invaluable in understanding what happened in 1994.
Using archived blood samples that had originally been taken for genetic analysis, Craig and his colleagues were able to go back and test for a number of viruses. The earliest year blood had been sampled was 1984, but because some of the lions sampled had been ten years old or older, he was able to infer information about when lions had been exposed to viruses as early as 1970.
They found that there had been previous outbreaks of canine distemper in the lions in 1977 and 1981. Because the lions had been studied then, he knew that these outbreaks had not caused large die-offs like the one that occurred in 1994. Instead, he found that by 1994, essentially all lions in Serengeti were free from canine distemper antibodies, meaning that none of the lions had any immunity to the disease. This widespread lack of immunity and a mutation in the virus were thought to have caused so many deaths.
The lion population recovered after the 1994 outbreak. Just years later, though, two “silent” outbreaks hit the population in 1999 and 2006. Unlike the 1994 outbreak, these ones were not noticed at the time because few lions died. They were only detected through blood sample testing. An analysis of the archived blood samples finally revealed the major difference between the canine distemper outbreak that led to massive death and those that did not. High death rates in the 1994 outbreak were due to the simultaneous infection with another disease — a protozoan parasite known as Babesia — that becomes increasingly common during and after major droughts. When Babesia is absent, lions contract canine distemper, but their immune systems fight it and they become immune. When lions are also infected with Babesia, they cannot fight off the canine distemper virus as easily, and more of them get sick and die.
The long-term lion data was also instrumental in understanding the spread of canine distemper in the 1994 outbreak. The disease showed up sporadically in the study area prides, suggesting that lions acquired the disease from an outside source, rather than spreading it from one lion to another. Sophisticated analyses revealed that the origin of the outbreak was likely in domesticated dogs in the human settlements around the Serengeti ecosystem. Further, it is likely that lions acquired the disease repeatedly from hyenas. Hyenas move great distances, use human-inhabited areas around the Serengeti more than lions do, and interact with lions at kills.
Scientists cannot predict major droughts. Nor can they predict wildlife disease outbreaks. It isn’t possible to recreate major droughts with experiments in vast wilderness areas. Nor is it ethical to introduce novel diseases into natural areas in order to understand more about the disease. It is ONLY through long-term research projects like the Serengeti Lion Project that we acquire the data necessary to understand what happens in nature during disease outbreaks, droughts, and other rare, but important events.
Ideally we would like to run Snapshot Serengeti for at least a decade. We want to be able to capture some drought years in our data set, and some years with unusually wet dry seasons. We want our cameras to be running when the next unexpected disease outbreak occurs — in lions or in other species. To those of you have already contributed to our crowd-funding campaign, a heartfelt thank you. If you haven’t yet, and are able, please consider a donation.
To read more about canine distemper, Babesia, and Serengeti lions, check out:
Munson, L., K.A. Terio, R. Kock, T. Mlengeya, M.E. Roelke, E. Dubovi, B. Summers, A.R.E. Sinclair & C. Packer. 2008. Climate extremes and co-infections determine mortality during epidemics in African lions. PLoS-One 3, e2545.