http://news.sciencemag.org/health/2015/ ... astern-u-sVolume 21, Number 10—October 2015
Heartland Virus Neutralizing Antibodies in Vertebrate Wildlife, United States, 2009–2014
Kasen K. Riemersma1 and Nicholas Komar
Author affiliations: Centers for Disease Control and Prevention, Fort Collins, Colorado, USA
Since its discovery in 2009, the tickborne Heartland virus (HRTV) has caused human illness in Missouri, Oklahoma, and Tennessee USA. To better assess the geographic distribution of HRTV, we used wildlife serology as an indicator. This retrospective evaluation determined that HRTV is widespread within the central and eastern United States.
Heartland virus (HRTV; family Bunyaviridae, genus Phlebovirus) is an emerging public health threat in the United States. HRTV disease, characterized by severe fever, leukopenia, and thrombocytopenia, was first reported in 2 farmers in northwestern Missouri in 2009 (1). Seven additional HRTV disease cases (2 fatal) have been reported in Missouri, Tennessee, and Oklahoma (2,3). A study of ticks and mosquitoes in northwestern Missouri detected HRTV infections only in Amblyomma americanum (lone star tick) and thus implicated this tick as a vector (4). The virus was isolated solely from deplete host-seeking nymphs, which presumably were infected as larvae after feeding on a viremic vertebrate host. Because HRTV has yet to be isolated from any wild or domestic animals, the question of vertebrate reservoir(s) remains unanswered. However, high prevalence of seropositive white-tailed deer (Odocoileus virginianus) and raccoon (Procyon lotor) from northwestern Missouri indicate these species as targets for wildlife serosurveillance (5).
The HRTV disease case reports in Tennessee and Oklahoma after the initial case reports in Missouri create the perception that HRTV transmission activity might be dispersing from an origin in northwestern Missouri. However, the geographic range of HRTV activity is unknown. HRTV distribution may mirror the range of the lone star tick, which is distributed throughout most of the central and eastern United States and recently has expanded northward (6). To investigate the hypothesis that HRTV activity occurs throughout the range of its putative tick vector, we conducted a retrospective serosurvey of mainly white-tailed deer and raccoon from 19 states within the heart and periphery of the lone star tick range to look for evidence of HRTV activity.
Banked blood samples collected from white-tailed deer, raccoon, and (occasionally) moose (Alces alces) and coyote (Canis latrans) during 2009–2014 were analyzed by plaque-reduction neutralization test for HRTV neutralizing antibodies by using African green monkey kidney (Vero) cell culture. Only samples from healthy live-trapped animals or deceased animals from anthropogenic causes (i.e., hunting, culls, and automobile strikes) were tested. Inclusion of 19 states was opportunistic based on sample availability. We used the plaque-reduction neutralization test to evaluate HRTV seropositivity for white-tailed deer (n = 396), raccoon (n = 949), coyote (n = 61), and moose (n = 22) (Table 1). Samples consisted of whole blood dried onto Nobuto strips (Advantec MFS, Inc., Dublin, CA, USA), bloody body cavity fluids, or hemolyzed whole blood. Nobuto strip samples were eluted to 1:10 serum dilution in phosphate buffer solution in accordance with the manufacturer’s instructions. All samples were heat-inactivated at 56°C for 45 min.
We screened the inactivated samples at 1:20 dilution by mixing serum diluted 1:10 with equal volume of titrated HRTV to approximate a challenge dose of 50 PFUs. Treated Vero cells were incubated for 1 h at 37°C, 5% CO2, before applying a nutrient-rich 0.5% agarose overlay. A second overlay containing Neutral Red was applied after 5–7 d of incubation. Viral plaques were counted 6–12 d after inoculation. A neutralization threshold of 70% relative to HRTV-only controls was used to determine positive samples. All screen-positive samples were repeat-tested to confirm results. Samples were considered seropositive if they were confirmed as positive at a dilution of >1:40. Comparative neutralization tests with related viruses were not performed, because we had previously found that murine antiserum developed against the other known phleboviruses in the United States—Sunday Canyon virus (7), Rio Grande virus (8), and Lone Star virus (9)—had no appreciable neutralizing activity against HRTV (Table 2). Human antiserum developed against HRTV exhibited weak 1-way neutralization of Lone Star virus and Sunday Canyon virus (Table 2).
Of 1,428 animals, 103 were seropositive: 55 deer, 33 raccoon, 11 coyotes, and 4 moose. Thirteen states had seropositive animals: Florida, Georgia, Illinois, Indiana, Kansas, Kentucky, Maine, Missouri, New Hampshire, North Carolina, Tennessee, Texas, and Vermont (Table 1; Figure 1). Within the 13 states, 20 geographic clusters of seropositive animals were mapped by plotting positive animals by the county where they were collected (Figure 2).
We provide evidence of widespread HRTV transmission activity across the central and eastern United States. Of 13 affected states, only Missouri and Tennessee had previous evidence of HRTV activity. A more stringent neutralization threshold of 80% would reclassify 14 positive samples to “equivocal,” but the number of positive states would remain unchanged. These findings should encourage clinicians and public health officials to consider HRTV as a potential source of illness throughout the eastern United States.
Surprisingly, seropositive white-tailed deer were detected in northern New England, where established populations of lone star ticks are unknown (6). Possible explanations include unreported lone star tick populations, immigration of seropositive deer, alternative tick vectors for HRTV, or presence of a serologically cross-reactive virus. Movement of deer across state boundaries is an unlikely explanation. Extensive lone star tick populations are not reported in neighboring states (6), and migration of deer from lone star tick–infested regions is unlikely (10). Savage et al. did not detect HRTV RNA in Dermacentor variabilis, the American dog tick (4), but additional tick species inhabit northern New England. Several tick species are reported to transmit severe fever with thrombocytopenia syndrome virus, a closely related phlebovirus found in eastern Asia (11). Further investigation of tick populations and their vector competence for HRTV is warranted, and production of HRTV neutralizing antibodies in response to a serologically similar virus should be investigated. Two new phleboviruses recently detected in Ixodes ticks in the northeastern United States are genetically unrelated to HRTV but raise the possibility that additional undiscovered phleboviruses exist (12). Severe fever with thrombocytopenia syndrome virus–reactive antibodies in wildlife were reported in Minnesota, also peripheral to the lone star tick geographic range, indicating the likely presence of HRTV or a similar virus there (13).
The finding of seropositive moose and coyotes indicates that these mammals are exposed to HRTV in certain situations and might be useful targets for serosurveillance, in addition to deer and raccoon. The full vertebrate host range and the reservoir competence of these mammals for HRTV remains unknown.
The chronology of dispersal of HRTV is unclear. Suggesting that HRTV emerged in northwestern Missouri and spread to neighboring states to the east and south is overly simplistic. Because animals were sampled at different points of time and space during this study, our data lack robustness to enable comparison of populations over time or between geographic locations. Thus, we are unable to evaluate the dynamics of HRTV spread. Furthermore, the proportions of HRTV-seropositive animal populations lack quantitative value because of our retrospective convenience sampling. Our results simply indicate that HRTV or a very similar virus has circulated in the sampled regions in the recent past and that this activity began as early as 2009. Adult seropositive white-tailed deer were detected in Maine and Florida in 2009, and based on the estimated ages of affected deer (data not shown), the infections could have occurred as early as 2003. A much larger retrospective serosurvey is necessary to elucidate HRTV’s history of emergence.
Dr. Riemersma was a veterinary student in the CDC Epidemiology Elective program at the Division of Vector-Borne Diseases during this study and is currently a PhD student at the University of California, Davis. His research interests include the genetics and ecology of pathogen emergence, with particular interest in vector-borne viruses.
Dr. Komar is the vertebrate ecologist for the Arbovirus Diseases Branch, Division of Vector-Borne Diseases, CDC, Fort Collins, Colorado. His major research interest is the role of vertebrate hosts in arbovirus transmission cycles.
This study was supported by the CDC Epidemiology Elective Program and funded by CDC.
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Oklahoma State Department of Health. Oklahoma State Health Department confirms first case and death of Heartland virus [cited 2014 Jul 2].http://www.ok.gov/health/Organization/O ... Virus.html
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Bosco-Lauth AM, Panella NA, Root JJ, Gidlewski T, Lash RR, Harmon JR, Serological investigations of Heartland virus (Bunyaviridae: Phlebovirus) exposure in wild and domestic animals adjacent to human case sites in Missouri 2012–2013. Am J Trop Med Hyg. 2015;92:1163–7.
Springer YP, Eisen L, Beati L, James AM, Eisen RJ. Spatial distribution of counties in the continental United States with records of occurrence of Amblyomma americanum (Ixodida: Ixodidae). J Med Entomol. 2014;51:342–51. Yunker CE, Clifford CM, Thomas LA, Keirans JE, Casals J, George JE, Sunday Canyon virus, a new ungrouped agent from the tick Argas (A.) cooleyi in Texas. [PubMed]. Acta Virol. 1977;21:36–44.
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The Lone Star tick's range may well be expanding. To what extent has yet to be determined:The Heartland virus may occur across the eastern U.S.
By Martin Enserink 18 September 2015 2:30 pm
A dangerous tick-borne virus that first surfaced in humans in Missouri in 2009 appears to be common in wildlife across the central and eastern United States, according to a new study. Researchers at the Centers for Disease Control and Prevention (CDC) in Fort Collins, Colorado, found evidence of the so-called Heartland virus in deer, raccoons, coyotes, and moose in 13 states. Doctors should be on the lookout for human patients, the researchers say, because they might go undetected. But other researchers say such warnings are premature.
The first known human cases of the Heartland virus were two farmers in northwestern Missouri. Both became very sick in 2009, with symptoms including fever, fatigue, headache, lack of appetite, nausea, and diarrhea. Both had also recently been bitten by ticks, but tests for the usual tick-borne suspects—such as several Ehrlichia species, a group of intracellular bacteria—came back negative. Both patients recovered, although one of them kept suffering from fatigue and headaches.
It wasn't until 3 years later, in 2012, that scientists reported that the patients had most likely been infected by a hitherto unknown agent. The virus, named after the Heartland Regional Medical Center in St. Joseph, Missouri, where the farmers had been treated, is a species of the genus Phlebovirus. That group also includes the mosquito-borne Rift Valley fever virus and several other agents linked to human disease.
Since then, seven more Heartland cases—including two fatal ones—have been reported in Missouri, Tennessee, and Oklahoma, and researchers have begun to unravel the virus's ecology and geographical spread. For a study published in 2013, they collected more than 50,000 ticks at the Missouri farms and elsewhere in the region; they found that the lone star tick, Amblyomma americanum, was the only species carrying the virus and thus most likely the culprit. Another study in northwestern Missouri, published last year, fingered white-tailed deer and raccoons as likely hosts for the virus. Ticks probably feed on these animals as tiny larvae in the late summer and fall, they concluded, and infect humans during the following spring and summer when they're nymphs.
In the new study, CDC's Nicholas Komar and Kasen Riemersma—who's now at the University of California, Davis—used existing blood samples from white-tailed deer, raccoons, moose, and coyotes collected between 2009 and 2014 in 19 states, both in the center of the lone star tick's range and its periphery, and tested them for antibodies against the Heartland virus. Out of 1428 animals, 103 tested positive, the researchers report in a paper posted this week in Emerging Infectious Diseases: 55 deer, 33 raccoons, 11 coyotes, and four moose.
The positive samples came from 20 geographical clusters spread out over 13 different states, from Maine to Texas. "These findings should encourage clinicians and public health officials to consider [Heartland virus] as a potential source of illness throughout the eastern United States," the duo writes.
But not everyone is convinced. The lone star tick doesn't occur in northern New England, so it's not clear why the Heartland virus would circulate there, says medical entomologist Durland Fish, a professor emeritus at Yale University. It may well be that the antibodies found by the team weren't directed against the Heartland virus but some other agent; it's not uncommon for cross-reactivity to occur in serological tests. In fact, Fish isn't convinced that the Heartland virus is tick-borne; the fact that it was found in ticks doesn't mean they also transmit the virus, he says. "The whole thing is very speculative.”
Komar acknowledges that the team was surprised to find evidence of the virus outside the lone star tick's range. There could be another tick species acting as host in the northern United States, he says. It's also possible that the antibodies were directed against another virus, as Fish suggests, he acknowledges—but if so, it would be a closely related and unknown phlebovirus, which still would be something to watch closely. "We wanted to raise awareness about this in the medical community," Komar says. But Fish says it's too early for that. "There's enough paranoia about tick-borne diseases out there right now.”
http://www.ncbi.nlm.nih.gov/pubmed/26217042J Med Entomol. 2014 Mar;51(2):342-51.
Spatial distribution of counties in the continental United States with records of occurrence of Amblyomma americanum (Ixodida: Ixodidae).
Springer YP, Eisen L, Beati L, James AM, Eisen RJ.
In addition to being a major nuisance biter, the lone star tick, Amblyomma americanum (L.), is increasingly recognized as an important vector of pathogens affecting humans, domestic animals, and wildlife. Despite its notoriety, efforts have been lacking to define the spatial occurrence ofA. americanum in the continental United States with precision beyond that conveyed in continental-scale distribution maps. Here we present a county-level distribution map for A. americanum generated by compiling collection records obtained from a search of the published literature and databases managed by the USDA, U.S. National Tick Collection, and Walter Reed Biosystematics Unit. Our decadal and cumulative maps, which visually summarize 18,121 collections made between 1898 and 2012, show that A. americanum is either established (> or = six ticks or -two life stages) or reported (<six ticks of a single life stage or number of ticks not specified) in 1,300 counties distributed among 39 states and the District of Columbia. Our cumulative map depicts a species with a core distributional area in the southern part of the eastern United States, but that also occurs further north, especially along the Atlantic Coast and into the Midwest. Although our decadal maps suggest a northward shift in the tick's distribution in recent decades, the lack of systematic tick surveillance makes this difficult to confirm. The data presented herein should aid in identifying areas posing risk for A. americanum-associated illnesses and environmental correlates that define the tick's distributional limits.
[PubMed - indexed for MEDLINE]
Am J Trop Med Hyg. 2015 Jul 27. pii: 15-0330. [Epub ahead of print]
Modeling the Present and Future Geographic Distribution of the Lone Star Tick, Amblyomma americanum (Ixodida: Ixodidae), in the Continental United States.
Springer YP1, Jarnevich CS2, Barnett DT2, Monaghan AJ2, Eisen RJ2.
1 Division of Vector-Borne Diseases, Centers for Disease Control and Prevention, Fort Collins, Colorado; U.S. Geological Survey, Fort Collins, Colorado; National Ecological Observatory Network, Inc., Boulder, Colorado; National Center for Atmospheric Research, Boulder, Colorado
2 Division of Vector-Borne Diseases, Centers for Disease Control and Prevention, Fort Collins, Colorado; U.S. Geological Survey, Fort Collins, Colorado; National Ecological Observatory Network, Inc., Boulder, Colorado; National Center for Atmospheric Research, Boulder, Colorado.
The Lone star tick (Amblyomma americanum L.) is the primary vector for pathogens of significant public health importance in North America, yet relatively little is known about its current and potential future distribution. Building on a published summary of tick collection records, we used an ensemble modeling approach to predict the present-day and future distribution of climatically suitable habitat for establishment of the Lone star tick within the continental United States. Of the nine climatic predictor variables included in our five present-day models, average vapor pressure in July was by far the most important determinant of suitable habitat. The present-day ensemble model predicted an essentially contiguous distribution of suitable habitat extending to the Atlantic coast east of the 100th western meridian and south of the 40th northern parallel, but excluding a high elevation region associated with the Appalachian Mountains. Future ensemble predictions for 2061-2080 forecasted a stable western range limit, northward expansion of suitable habitat into the Upper Midwest and western Pennsylvania, and range contraction along portions of the Gulf coast and the lower Mississippi river valley. These findings are informative for raising awareness of A. americanum-transmitted pathogens in areas where the Lone Star tick has recently or may become established.
© The American Society of Tropical Medicine and Hygiene.
[PubMed - as supplied by publisher]
http://www.mvtimes.com/2015/05/27/marth ... illnesses/
Martha’s Vineyard hits peak time for tickborne illnesses
by Barry Stringfellow - May 27, 2015
This year, there’s a buzz about a new bad guy in town — the Lone Star tick.
Lone Star rides into town
While it’s premature to say if the Lone Star tick has colonized on the Vineyard, anecdotally and on social media, many Islanders have reported finding them for the first time this year.
The Lone Star tick has been on Martha’s Vineyard in small numbers for some time, according to Mr. Telford. It’s had a mysterious presence. “I’ve seen them here as early as the late ’90s, and I found them in Nantucket in the late ’80s,” he said. “But they fizzle. Why is that? On Prudence Island in Narragansett Bay they’ve been around since the 1960s, and [people] have a horrible problem with them. But you don’t see them on Bristol or any of the nearby islands. It’s a huge mystery.”
Unlike deer ticks and dog ticks, the Lone Star tick is an aggressive predator. “They’re nasty; they have eyes, unlike deer ticks that are blind,” Mr. Telford said. “They can see you and come after you.”
The female Lone Star tick is often distinguished by the white “star” on its back; however, not all Lone Star ticks have the white spot. “All, however, are round and brown,” Mr. Telford said. “All move fast.”
Until recently, the Lone Star tick was primarily found south of the Mason-Dixon Line. But as the climate has warmed, the infectious insect has spread its range.
The Lone Star tick has now colonized on Cuttyhunk, Nashawena, and Prudence Island.
Mr.Telford said that he discovered the Lone Star tick infestation on Cuttyhunk five years ago. “People were raising the flag, saying there are no Lone Star ticks in Massachusetts, but then I went to Cuttyhunk to give a talk, and said, ‘We’ve got a problem here.’”
The Lone Star tick is a vector for Rocky Mountain spotted fever as well as tularemia, ehrlichiosis, and Masters’ disease. Rocky Mountain spotted fever symptoms include nausea, vomiting, high fever, chills, muscle aches, insomnia, and a red, non-itchy rash that usually appears on wrists and ankles, and spreads in both directions. According to the Columbia University Lyme and Tick Borne Disease research center, about 3 percent to 5 percent of patients who are infected with Rocky Mountain spotted fever will die from it. The telltale rash will show up in five to 10 days, but 10 to 15 percent of those infected never get the rash.
“It’s not just diseases you can get from Lone Star ticks; for some reason, some people develop an allergy to red meat,” Mr. Telford said, citing a recent connection made by a study at the University of Virginia Medical School.
Mr. Telford stressed preventive measures have to be taken immediately so Martha’s Vineyard doesn’t become rife with Lone Star ticks. “We think this should be nipped in the bud,” he said. “Let’s not talk about it, let’s not research it anymore, let’s just follow up on the reports, and go to the site and investigate. This is a way citizens can get involved to prevent the problem.”
[snip] “If it’s a homeowner, we’ll see if it’s OK to spray pesticide,” Mr. Telford said. “If it’s conservation land, we’ll find some way to get rid of them. If you get volunteers and drag the area day after day, you can get rid of them.”
Mr. Telford [says] “The deer tick female lays 2,000 eggs. The Lone Star tick lays 6,000 eggs, so it doesn’t take long to build up a population,” he said. “Let’s do something about this while we can.”