In his presentation on anthropogenic factors in tick-borne pathogen emergence, Durland Fish of Yale University focused on the “steadily increasing” presence of tick-borne disease in the northeastern United States associated with the reversal of deforestation in that region (see Summary and Assessment subsection entitled “Reforestation and Tick-Borne Disease”). In addition to Lyme disease, which rose from obscurity to become the country’s most common vector-borne disease within the span of two decades, black-legged deer ticks (Ixodes scapularis) serve as the vector for Anaplasma phagocytophilum—a bacterium that causes a flu-like illness called human granulocytic anaplasmosis—and the protozoan Babesia microti can be spread by transfused blood from an infected human.
The adults of this tick species feed exclusively on white-tailed deer; only the nymphs feed on and transmit pathogens to humans. The decline of agriculture in the northeastern United States and the subsequent reforestation of this region over the past several decades have provided an ideal habitat for increasing numbers of white-tailed deer, their attendant ticks, and the pathogens they bear. This trend may well continue and gain momentum, Fish noted, since various non-native tick-borne arboviruses could infect any of several hundred human-feeding species of ticks present in the United States.
Although vector-borne plant diseases share many ecological and epidemiological features with their animal and human counterparts, they tend to be studied in isolation. In his contribution to this chapter, presenter Rodrigo Almeida of the University of California, Berkeley, argues that new insights on the nature of vector-borne diseases could be gained through the exchange of tools and ideas among disparate research communities. Plant systems, for example, “allow large experiments to be conducted, with multiple hosts, vector species and pathogen strains, which could be used to experimentally address ecological and evolutionary hypotheses on pathogen range and transmission efficiency,” he explains. In describing the rise of Pierce’s disease of grapevines in California following the recent introduction of a highly efficient insect vector for a local bacterial pathogen, Almeida explores a common pattern of vector-borne disease emergence from an agricultural perspective.
The final essays in this chapter address the profound influence of climate on vector-borne disease distribution and transmission. The first, by presenter Kenneth Linthicum of the U.S. Department of Agriculture’s (USDA’s) Agricultural Research Service (ARS) Center for Medical, Agricultural, and Veterinary Entomology and co-authors, focuses on the effects of regional variations in temperature and rainfall on vector-borne disease transmission. The primary driver of global climate variability, the periodic warming of the Pacific Ocean surface known as the El Niño/Southern Oscillation (ENSO), has been linked with outbreaks of a variety of arthropod-borne diseases, the authors note. In the case of Rift Valley fever (RVF), this association was sufficiently strong to permit them to develop risk maps that successfully predicted a major outbreak in Africa in