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Surveillance of potential hosts and vectors of scrub typhus in Taiwan.

Kuo CC, Lee PL, Chen CH, Wang HC - Parasit Vectors (2015)

Bottom Line: PCR products were further sequenced to reveal probable OT strains.Seropositivity rate for OT exposure in 876 assayed rodents was 43.0% and OT positivity rate in 347 pools of chiggers was 55.9%, with 15 OT strains identified in the 107 successfully sequenced samples.It also emphasizes the importance of recognition of chigger vectors and their vertebrate hosts for a better prediction of human risks to scrub typhus under rapid environmental changes.

View Article: PubMed Central - PubMed

Affiliation: Department of Life Science, National Taiwan Normal University, Taipei, Taiwan. cckuo@ntnu.edu.tw.

ABSTRACT

Background: Scrub typhus is a lethal infectious disease vectored by larval trombiculid mites (i.e. chiggers) infected with Orientia tsutsugamushi (OT) and recent decades have witnessed an emergence of scrub typhus in several countries. Identification of chigger species and their vertebrate hosts is fundamental for the assessment of human risks to scrub typhus under environmental changes, but intensive and extensive survey of chiggers and their hosts is still lacking in Taiwan.

Methods: Chiggers were collected from shrews and rodents in nine counties of Taiwan and were assayed for OT infections with nested polymerase chain reaction (PCR). PCR products were further sequenced to reveal probable OT strains. Rodents were assessed for OT exposure by immunofluorescent antibody assay. Lastly, incidence rate of scrub typhus in each county was associated with loads and prevalence of chigger infestations, seropositivity rate in rodents, and OT positivity rate in chiggers.

Results: Rattus losea was the most abundant (48.7% of 1,285 individuals) and widespread (occurred in nine counties) small mammal species and hosted the majority of chiggers (76.4% of 128,520 chiggers). Leptotrombidium deliense was the most common (64.9% of all identified chiggers) and widespread (occurred in seven counties) chigger species but was replaced by Leptotrombidium pallidum or Leptotrombidium scutellare during the cold seasons in two counties (Matsu and Kinmen) where winter temperatures were lower than other study sites. Seropositivity rate for OT exposure in 876 assayed rodents was 43.0% and OT positivity rate in 347 pools of chiggers was 55.9%, with 15 OT strains identified in the 107 successfully sequenced samples. Incidence rate of scrub typhus was positively correlated with chigger loads, prevalence of chigger infestations, seropositivity rate but not OT positivity rate in chiggers.

Conclusions: Our study reveals R. losea as the primary host for chiggers and there exists a geographical and seasonal variation in chigger species in Taiwan. It also emphasizes the importance of recognition of chigger vectors and their vertebrate hosts for a better prediction of human risks to scrub typhus under rapid environmental changes.

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Related in: MedlinePlus

Study sites for the collection and identification of Orientia tsutsugamushi (OT) strains in chiggers from small mammal hosts in Taiwan during 2006–2010. a mean temperature for the coldest and hottest months (shown in parenthesis); b OT strains and genotypes (in parenthesis) identified in chiggers
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Fig1: Study sites for the collection and identification of Orientia tsutsugamushi (OT) strains in chiggers from small mammal hosts in Taiwan during 2006–2010. a mean temperature for the coldest and hottest months (shown in parenthesis); b OT strains and genotypes (in parenthesis) identified in chiggers

Mentions: From 2006 to 2010, small mammals (rodents and shrews) were trapped in different parts of Taiwan, including eastern (Yilan, Hualien, Taitung), western (Taoyuan, Taichung, Kaoping), and main islets near Taiwan (Matsu, Kinmen, Penghu) (Fig. 1). These nine counties vary profoundly in the incidence rate of scrub typhus (2001–2005, 0.2 to 125.2 cases per 100,000 people per year; on-line data, Taiwan National Infectious Disease Statistics System, http://nidss.cdc.gov.tw/). Mean temperature for the hottest month (typically in July in Taiwan) is similar among the nine study sites (27.1 °C–29.3 °C, Taiwan Central Weather Bureau) while mean temperature for the coldest month (typically in January) is more varied (8.9 °C–19.5 °C), with lower January temperature occurring in Matsu (8.9 °C) and Kinmen (12.8 °C) (Fig. 1a). Because scrub typhus prevails mainly in rural areas and occurs outside house [12], trappings were limited to the field but not implemented inside or close to human buildings. At each county, 80 Sherman traps (26.5 × 10 × 8.5 cm) and 80 Taiwan made rodent traps (27 × 16 × 13 cm) were deployed and baited with sweet potato covered with peanut butter. Each county was surveyed for four consecutive nights and surveyed at least twice (Yilan: March and August 2009; Hualien: May and November 2006, April 2009; Taitung: September 2006, June and September 2009; Taoyuan: March and October 2010; Taichung: March 2009, July 2010; Kaoping: February and May 2010; Matsu: March and July 2007; Kinmen: June 2006, January 2007, March 2008; Penghu: May and September 2007). Each night, traps were set up at different locations within the same county to maximize trapping coverage. Trapped small mammals (shrews and rodents) were euthanized with an overdose of Zoletil 50 (Virbac SA, Carros, France), and blood was collected by cardiac puncture. Chiggers recovered from small mammals were preserved in 70 % ethanol and stored at−70 °C until subsequent molecular detection of OT.Fig 1


Surveillance of potential hosts and vectors of scrub typhus in Taiwan.

Kuo CC, Lee PL, Chen CH, Wang HC - Parasit Vectors (2015)

Study sites for the collection and identification of Orientia tsutsugamushi (OT) strains in chiggers from small mammal hosts in Taiwan during 2006–2010. a mean temperature for the coldest and hottest months (shown in parenthesis); b OT strains and genotypes (in parenthesis) identified in chiggers
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4666075&req=5

Fig1: Study sites for the collection and identification of Orientia tsutsugamushi (OT) strains in chiggers from small mammal hosts in Taiwan during 2006–2010. a mean temperature for the coldest and hottest months (shown in parenthesis); b OT strains and genotypes (in parenthesis) identified in chiggers
Mentions: From 2006 to 2010, small mammals (rodents and shrews) were trapped in different parts of Taiwan, including eastern (Yilan, Hualien, Taitung), western (Taoyuan, Taichung, Kaoping), and main islets near Taiwan (Matsu, Kinmen, Penghu) (Fig. 1). These nine counties vary profoundly in the incidence rate of scrub typhus (2001–2005, 0.2 to 125.2 cases per 100,000 people per year; on-line data, Taiwan National Infectious Disease Statistics System, http://nidss.cdc.gov.tw/). Mean temperature for the hottest month (typically in July in Taiwan) is similar among the nine study sites (27.1 °C–29.3 °C, Taiwan Central Weather Bureau) while mean temperature for the coldest month (typically in January) is more varied (8.9 °C–19.5 °C), with lower January temperature occurring in Matsu (8.9 °C) and Kinmen (12.8 °C) (Fig. 1a). Because scrub typhus prevails mainly in rural areas and occurs outside house [12], trappings were limited to the field but not implemented inside or close to human buildings. At each county, 80 Sherman traps (26.5 × 10 × 8.5 cm) and 80 Taiwan made rodent traps (27 × 16 × 13 cm) were deployed and baited with sweet potato covered with peanut butter. Each county was surveyed for four consecutive nights and surveyed at least twice (Yilan: March and August 2009; Hualien: May and November 2006, April 2009; Taitung: September 2006, June and September 2009; Taoyuan: March and October 2010; Taichung: March 2009, July 2010; Kaoping: February and May 2010; Matsu: March and July 2007; Kinmen: June 2006, January 2007, March 2008; Penghu: May and September 2007). Each night, traps were set up at different locations within the same county to maximize trapping coverage. Trapped small mammals (shrews and rodents) were euthanized with an overdose of Zoletil 50 (Virbac SA, Carros, France), and blood was collected by cardiac puncture. Chiggers recovered from small mammals were preserved in 70 % ethanol and stored at−70 °C until subsequent molecular detection of OT.Fig 1

Bottom Line: PCR products were further sequenced to reveal probable OT strains.Seropositivity rate for OT exposure in 876 assayed rodents was 43.0% and OT positivity rate in 347 pools of chiggers was 55.9%, with 15 OT strains identified in the 107 successfully sequenced samples.It also emphasizes the importance of recognition of chigger vectors and their vertebrate hosts for a better prediction of human risks to scrub typhus under rapid environmental changes.

View Article: PubMed Central - PubMed

Affiliation: Department of Life Science, National Taiwan Normal University, Taipei, Taiwan. cckuo@ntnu.edu.tw.

ABSTRACT

Background: Scrub typhus is a lethal infectious disease vectored by larval trombiculid mites (i.e. chiggers) infected with Orientia tsutsugamushi (OT) and recent decades have witnessed an emergence of scrub typhus in several countries. Identification of chigger species and their vertebrate hosts is fundamental for the assessment of human risks to scrub typhus under environmental changes, but intensive and extensive survey of chiggers and their hosts is still lacking in Taiwan.

Methods: Chiggers were collected from shrews and rodents in nine counties of Taiwan and were assayed for OT infections with nested polymerase chain reaction (PCR). PCR products were further sequenced to reveal probable OT strains. Rodents were assessed for OT exposure by immunofluorescent antibody assay. Lastly, incidence rate of scrub typhus in each county was associated with loads and prevalence of chigger infestations, seropositivity rate in rodents, and OT positivity rate in chiggers.

Results: Rattus losea was the most abundant (48.7% of 1,285 individuals) and widespread (occurred in nine counties) small mammal species and hosted the majority of chiggers (76.4% of 128,520 chiggers). Leptotrombidium deliense was the most common (64.9% of all identified chiggers) and widespread (occurred in seven counties) chigger species but was replaced by Leptotrombidium pallidum or Leptotrombidium scutellare during the cold seasons in two counties (Matsu and Kinmen) where winter temperatures were lower than other study sites. Seropositivity rate for OT exposure in 876 assayed rodents was 43.0% and OT positivity rate in 347 pools of chiggers was 55.9%, with 15 OT strains identified in the 107 successfully sequenced samples. Incidence rate of scrub typhus was positively correlated with chigger loads, prevalence of chigger infestations, seropositivity rate but not OT positivity rate in chiggers.

Conclusions: Our study reveals R. losea as the primary host for chiggers and there exists a geographical and seasonal variation in chigger species in Taiwan. It also emphasizes the importance of recognition of chigger vectors and their vertebrate hosts for a better prediction of human risks to scrub typhus under rapid environmental changes.

Show MeSH
Related in: MedlinePlus