We begin with the study of Randolph and Rogers (2000), who report that tick-borne encephalitis (TBE) "is the most significant vector-borne disease in Europe and Eurasia," having "a case morbidity rate of 10-30% and a case mortality rate of typically 1-2% but as high as 24% in the Far East." The disease is caused by a flavivirus (TBEV), which is maintained in natural rodent-tick cycles; and humans may be infected with it if bitten by an infected tick or by drinking untreated milk from infected sheep or goats.

Early writings on the relationship of TBE to global warming predicted it would expand its range and become more of a threat to humans in a warmer world. However, Randolph and Rogers indicate that "like many vector-borne pathogen cycles that depend on the interaction of so many biotic agents with each other and with their abiotic environment, enzootic cycles of TBEV have an inherent fragility," so that "their continuing survival or expansion cannot be predicted from simple univariate correlations," as is commonly done by climate alarmists intent on scaring people into reducing CO2 emissions on the basis of false premises. Hence, the two researchers decided to explore the subject in greater detail than had ever been done before.

Confining their analysis to Europe, Randolph and Rogers first matched the present-day distribution of TBEV to the present-day distributions of five climatic variables: monthly mean, maximum and minimum temperatures, plus rainfall and saturation vapor pressure, "to provide a multivariate description of present-day areas of disease risk." Then, they applied this understanding to outputs of a general circulation model of the atmosphere that predicted how these five climatic variables may change in the future.

The results of these operations indicated that the distribution of TBEV might expand both north and west of Stockholm, Sweden, in a warming world. For most other parts of Europe, however, the two researchers say that "fears for increased extent of risk from TBEV caused by global climate change appear to be unfounded." In fact, they found that "the precise conditions required for enzootic cycles of TBEV are predicted to be disrupted" in response to global warming, and that the new climatic state "appears to be lethal for TBEV." This finding, in their words, "gives the lie to the common perception that a warmer world will necessarily be a world under greater threat from vector-borne diseases." In the case of TBEV, in fact, they report that the predicted change "appears to be to our advantage."

Also reporting that "it is often suggested that one of the most important societal consequences of climate change may be an increase in the geographic distribution and transmission intensity of vector-borne disease," Estrada-Peņa (2003) evaluated the effects of various abiotic factors on the habitat suitability of four tick species that are major vectors of livestock pathogens in South Africa. This work revealed that "year-to-year variations in the forecasted habitat suitability over the period 1983-2000 show a clear decrease in habitat availability, which is attributed primarily to increasing temperature in the region over this period." In addition, when climate variables were projected to the year 2015, Estrada-Peņa found that "the simulations show a trend toward the destruction of the habitats of the four tick species," which is just the opposite of what is seemingly incessantly predicted by climate alarmists.

Another scientist who has noted that many people "assume a correlation between increasing disease incidence and global warming" is Zell (2004), who reviewed the scientific literature pertaining to the subject and determined that "the factors responsible for the emergence/reemergence of vector-borne diseases are complex and mutually influence each other," citing as an example of this complexity the fact that "the incidence and spread of parasites and arboviruses are affected by insecticide and drug resistance, deforestation, irrigation systems and dams, changes in public health policy (decreased resources of surveillance, prevention and vector control), demographic changes (population growth, migration, urbanization), and societal changes (inadequate housing conditions, water deterioration, sewage, waste management)."

In light of these many complicating factors, Zell says "it may be over-simplistic to attribute emergent/re-emergent diseases to climate change and sketch the menace of devastating epidemics in a warmer world." Indeed, he concludes that "variations in public health practices and lifestyle can easily outweigh changes in disease biology," especially those that might be caused by global warming. What is more, these public health and lifestyle changes could be implemented now, if we chose to do so, and at only a tiny fraction of the cost that would be needed to make even the smallest of changes in the future course of earth's air temperature. If we are truly worried about the status of vector-borne diseases in a warmer world, this is the tack we should take.

References
Estrada-Peņa, A. 2003. Climate change decreases habitat suitability for some tick species (Acari: Ixodidae) in South Africa. Onderstepoort Journal of Veterinary Research 70: 79-93.

Randolph, S.E. and Rogers, D.J. 2000. Fragile transmission cycles of tick-borne encephalitis virus may be disrupted by predicted climate change. Proceedings of the Royal Society of London Series B 267: 1741-1744.

Zell, R. 2004. Global climate change and the emergence/re-emergence of infectious diseases. International Journal of Medical Microbiology 293, Suppl. 37: 16-26.