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4 Emerging Infections, Tick Biology, and Host–Vector Interactions
Pages 37-60

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From page 37...
... Fortunately, new molecular tools and analytical techniques such as gene sequencing and analysis have enabled scientists to gain insights into tick biology and have resulted in a better understanding of TBDs. New technologies have also revealed a diverse microbial community associated with ticks that include viruses, bacteria, protozoans, and fungi.
From page 38...
... . In this chapter, five scientists examined the natural history of ticks and their wildlife and domestic hosts; outlined the contributions of animal health experts to understanding human TBD; explored genetic diversity among pathogens, vectors, and hosts; and showed how scientists investigate the microbial community found within the ticks to better understand the human risk for tick-borne diseases.
From page 39...
... The heat shock protein is primarily expressed in mammalian cells, but less so in tick cells, perhaps reflecting the lower incubation temperature in the tick. However, a "housekeeping" gene required by the organism seems to be equally expressed in all cell lines, independent of their origin.
From page 40...
... variabilis (the Rocky Mountain wood tick and American dog tick, respectively) , Rhipicephalus sanguineus (the brown dog tick)
From page 41...
... The regions of the plasmid encoding the parA and DnaA genes, which are important in plasmid maintenance and replication, along with a selectable and fluorescent traceable marker, were subcloned into pGEM. Subsequently, screening of a pRAM18 library yielded evidence of another R
From page 42...
... In contrast to hard ticks in which the adults feed only once, soft tick adults can feed multiple times. Not much is known about the evolution of ticks, as fossil ticks found in amber dating back 94 million years look like ticks of today (Klompen and Grimaldi, 2001)
From page 43...
... hermsi ticks are nocturnal and fast feeding, and usually feed on people sleeping in tick-infested cabins. Relapsing fever occurs in Africa, but it also occurs in the western United States, where it is underdiagnosed and underreported.
From page 44...
... However, broad fluctuations of the tick population occur from year to year. Tick populations in Westchester County north of New York City, Prudence Island in Narragansett Bay, and Fire Island off Long Island have similar yearly fluctuations, which suggests that whatever controls these fluctuations is occurring on
From page 45...
... Hosts, especially mammals and birds, vary significantly in their reservoir competence. Some domestic animals, such as dogs, are competent reservoirs for Lyme disease.
From page 46...
... In the South, lizards, the primary hosts for Ixodes scapularis, are not good reservoirs, so expanding the diversity of hosts in that region could actually increase the incidence of Lyme disease. Vector diversity can also affect the likelihood of human disease.
From page 47...
... As discussed previously in the report, there are changing dynamics that will affect human disease. For example, tick distribution is expanding up the Hudson Valley in New York, into northern New Jersey, down into the Southeast, and into Illinois, and modeling suggests that the tick will expand further into Canada.
From page 48...
... It would be difficult because of the divergence of ticks to make generalizations. Ginsberg noted that there is active research on the use of pheromones to enhance tick management methods by attracting ticks to the pesticides, but nothing is commercially available.
From page 49...
... For example, in a newly endemic area, the same species might be a good reservoir because it has not developed that type of immune response. Ginsberg noted that this might occur in nature and there may also be differences during the life cycle of the hosts, such that juveniles have a different reservoir competence than do adults.
From page 50...
... rickettsii are nearly identical to those of humans with Rocky Mountain spotted fever. In the context of one medicine, veterinary medicine and human medicine can both provide key insights into TBDs.
From page 51...
... . Similar insights from naturally occurring infection in animals have enhanced understanding of human diseases due to other tick-borne pathogens.
From page 52...
... As a result of sharing information across disciplines, across species, and across continents, granulocytic anaplasmosis was subsequently confirmed in cats and dogs in the northeastern United States and human anaplasmosis was reported in Sweden, Germany, Austria, and many other European and Asian countries. Another opportunity for which veterinary research can provide insight into human disease is by using dogs as a naturally occurring model of disease.
From page 53...
... Furthermore, there is a critical need to understand the role of vector-borne organisms as a cause of chronic disease in animals and humans. Finally, public education is important in preventing illness and death from acute infectious TBDs, such as anaplasmosis, ehrlichiosis, and Rocky Mountain spotted fever.
From page 54...
... scapularis bite humans in the southeastern United States, but nymphs rarely do. • There is a wider diversity of vertebrate hosts of ticks in the south eastern United States, particularly reptiles, which probably serves to dilute incidence of B
From page 55...
... minor ticks found on a single Carolina wren in South Carolina underscores the great diversity of those strains. In nymphal ticks on a Carolina wren, two different genetic groups of B
From page 56...
... burgdorferi, and among their animal hosts, there is significant genetic diversity. For example, we isolated 53 Borrelia strains in I
From page 57...
... scapularis do bite humans in the South. • The southeastern United States has a wider diversity of vertebrate hosts, particularly reptiles, than does the northeastern United States, which may dilute the risk of human exposure.
From page 58...
... CONCLUDING THOUGHTS ON EMERGING INFECTIONS, TICK BIOLOGY, AND HOST–VECTOR INTERACTIONS Lonnie King, D.V.M., M.S., M.A., College of Veterinary Medicine, Ohio State University Because many TBDs are zoonotic, animal and human health experts urgently need to collaborate and to develop an integrated surveillance system that includes domestic animals, wildlife, ticks, and people. Wider and more effective surveillance could allow animals to serve as sentinels and surrogates for human risk and exposure to TBDs.
From page 59...
... burgdorferi in the Southeast also suggests the possibility that human risk in this region may be underrecognized and that the epidemiology is certainly poorly understood. The impact of regional differences in tick populations, hosts, habitats, and pathogens on human disease -- and of genetically distinct subpopulations of those pathogens -- deserve further study.


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