COLUMBIA — The weather has cooled, and the arrival of fall means an end to a tick season that saw the number of tick-borne illnesses double statewide from the previous year.
According to preliminary statistics collected by the Missouri Department of Health and Senior Services, the two diseases that increased the most from 2006 to 2007 were Rocky Mountain spotted fever, with 354 cases across Missouri, and ehrlichiosis, with 199 cases. A similar trend was also seen in Boone County, where the number of reported ehrlichiosis cases went from eight in 2006 to 14 in 2007. The number of cases of Rocky Mountain spotted fever reported in Boone County went from four in 2006 to 18 in 2007.
EhrlichiosisThe Missouri Department of Health and Human Services recognizes two types of the disease, human granulocytic ehrlichiosis and human ehrlichiosis. The Centers for Disease Control and Prevention recognizes a third type, Ehrlichia ewingii. Symptoms: Often similar to the flu,symptoms begin to appear five to 10 days after being bitten. They include fever, headaches and muscle soreness. Risk: Can be deadly, but is treatable with antibiotics such as doxycycline.
Rocky Mountain spotted feverIn 2007, cases of this tick-borne disease were the most common. It is also the most dangerous of the tick-borne diseases. Symptoms: Initially flu-like, including fever, nausea, vomiting, severe headache, muscle pain and lack of appetite. Later, a pink-spotted rash and more serious symptoms develop. Risk: Potentially fatal but treatable with antibiotics if diagnosed quickly.
TularemiaTick bites are one of the ways to contract tularemia, which is considered very infectious by the CDC. However, it is not known to spread from one human to another. The disease can also be contracted by handling infected animals or eating or drinking contaminated food or water. Symptoms: Begin to appear after three to five days and include sudden fever, chills, headaches, diarrhea, muscle aches, joint pain and dry cough. Risk: Occasionally severe and possibly fatal. Typical treatment is with antibiotics in the tetracycline and chloramphenicol families.
Lyme-like diseasesStatistics of Lyme disease reported by the state are actually the less-serious Lyme-like diseases, said Karen Yates, vector-borne disease program coordinator for the Missouri Department of Health and Senior Services. These diseases display the bulls-eye rash and are similar to Lyme disease but test negative. At this time, more specific information about symptoms, risks or treatment is not available, Yates said. Source: Centers for Disease Control and Prevention; Missouri Department of Health and Senior Services
Ehrlichiosis was cited in the August death of a 15-year-old Centralia girl.
There was also a significant increase in diagnosed cases of the two other tick-borne diseases across Missouri: tularemia and Lyme-like diseases. There were no cases of either diesease in Boone County the past two years. All four tick-borne diseases are treatable if diagnosed early.
“Why there’s more cases (of ehrlichiosis) in humans is a bit of a puzzle,” said Bob Thach, professor of biology and dean of graduate arts and sciences at Washington University. “We’d love to know, but we don’t really have any good insights as to why.”
Thach and his team have been researching the tick population for three years. They have been working to find out which animals are the most common primary carriers of the bacteria that causes ehrlichiosis. The answer is unknown.
Possible explanations for the rise in diagnoses of tick-borne diseases differ from scientist to scientist.
Mary Spratt, a professor of biology at William Woods University who researches ehrlichiosis, said there are a number of possible explanations for the trend. Warmer winters have caused a larger portion of the tick population to survive until April. Lack of controlled burning and wild fires have also allowed more ticks to survive, and a large deer population could help ticks flourish. Also, people are moving out into more rural and suburban areas and there is rising awareness among doctors of the diseases.
“All of these things work together to cause the higher level of diagnosed cases we’re seeing now,” Spratt said.
Brian Allan, a graduate student at Washington University, believes that significant changes to the landscape can increase the tick population. Logging, urbanization and fire management create better habitats for tick hosts, like deer and mice, he said.
“They all have the potential to impact the hosts and impact the ticks themselves,” Allan said.
Thach said that while increases in the tick population might contribute to the higher number of illnesses, he doubts there has been a large jump in the tick population, citing instead a steady increase over the past 30 years.
“I’d be surprised if the tick population has doubled in the past two years,” Thach said.
Not everyone agrees that there has been an increase of tick-borne diseases, despite the preliminary numbers reported to the state health department.
“I don’t believe it, at least not across the board,” said Dr. Gregory Storch, director of Division of Infectious Diseases at the St. Louis Children’s Hospital. “You have to talk about each (disease) individually.”
He said he had some doubts on how well the cases were documented, especially with Rocky Mountain spotted fever, because the only noticeable increase he’d seen at the St. Louis Children’s Hospital is in ehrlichiosis.
Tick season typically ends in mid-September; it will begin again in April.
“I think the spike in cases shouldn’t prevent people from enjoying outside,” said Michael Cooperstock, professor of pediatric infectious diseases at University Hospital. “Do tick checks on yourself and your children at the end of the day. Many of the more serious (diseases) require for the tick to be attached for many, many hours.”