Climate crisis

Climate change is likely to dominate almost every aspect of our existence on the planet in the upcoming years. Climate scientists have noted that atmospheric carbon has increased over 40% since the middle of the 19th century and that this is attributable to human activity. The United Nations Intergovernmental Panel on Climate Change has warned that in 90 years we can expect an increase of 1.8°C to 4.0°C in average global temperature and a rise in sea level between 18 and 59 cm. In Canada, the overall rate of warming has been greater than twice the global mean and the rate in the north has been about 3 times the global mean (1). A temperature increase of about 5°C is expected for much of Canada in 50 years (1).

Direct effects of climate change include increased heat stress, floods, droughts, intense storms, thawing permafrost, melting sea ice. We have already experienced these and the expectation is that these changes will intensify. Indirect effects include spread of disease vectors, displacement of people and animals, forest fires, and food insecurity.

Veterinarians have a particular interest in projected changes in the spectrum and nature of animal diseases. So far, much of the deliberation has been about infectious diseases, particularly those whose agents have an environmental phase, those with a specific vector, and those that are transmissible to humans.

The French have identified Rift Valley fever, West Nile virus infection, visceral leishmaniasis, leptospirosis, bluetongue, and African horse sickness as diseases most likely to be affected by global warming in France. In Canada, the risks seem highest for spread of West Nile virus, leptospirosis, and blue tongue. West Nile virus, following its appearance in North America in 1999, has spread rapidly (often associated with high environmental temperatures, heavy rains, and explosions in the mosquito population) and is now found from Canada to Argentina.

Canine leptospirosis re-emerged in North America around the mid-1990s and an increase in seroprevalence was demonstrated in Ontario over the period 1998 to 2006 (2). Bluetongue, a vector-borne viral disease of importance in sheep is not usually found in Canada although it is endemic in the United States. Cattle act as a reservoir for the virus and sporadic infections have been found in cattle in British Columbia and Ontario, likely due to transmission by midges from the United States. In addition, northward migration of the blacklegged tick Ixodes scapularis will likely further expand the regions in Canada in which Lyme disease is endemic (3). Frequency of Lyme disease cases in Canada increased 6-fold during the period 2009 to 2015 and 13-fold between 2009 and 2017. This has been associated with an increase in degree days above 0°C and an expansion in the range of the ticks that carry Borrelia burgdorferi.

Climate change also carries animal health risks not related to vector-borne diseases. These include heat stress, feed shortages, importation of rescued dogs with various disease agents, and disruptions in ocean life. There are also unpredictable developments, especially those associated with co-infections or interplay between host, environment, pathogens, and vectors. A good example of surprising results of co-infection due to an increase in extreme weather is the development of lethal canine distemper in lions in Tanzania in the late 1900s. Prolonged droughts had led to a weakening of the herbivore population and massive propagation of ticks that lived on the herbivores. Lions that fed on the herbivores became infected with large numbers of the parasite Babesia leo, which was carried by the ticks. The Babesia infection reduced the lions’ immunity and allowed a non-fatal canine distemper infection to become fatal.

It is incumbent on us to do all we can to promote steps to address the climate crisis. As individuals, we can decrease our energy use and opt for renewable energy when possible. Our professional organization can intensify its existing efforts to promote a green environment. Importantly, we need to urge governments at all levels to be aggressive in implementing mitigation and adaptation strategies.