Minnesota Department of Health (MDH) Bug Bytes
May 14, 2001
Vol. 2: No. 10
It's spring and as such our thoughts turn to animals
1. The Deer Ticks Are Coming! The Deer Ticks Are Coming!
During 2000, record numbers of Lyme disease and human granulocytic ehrlichiosis (HGE) cases were reported in Minnesota residents. Lyme disease cases rose from 283 in 1999 to 465 in 2000 (64% increase). HGE cases increased even more dramatically from 36 reported in 1999 to 79 in 2000 (119% increase). Some of these increases were likely due to better reporting (thank you for your help!), but much of the increase may have been due to factors in the field such as weather, increasing deer tick infection rates, or more human activity in tick habitat. It is difficult to predict how bad our tick-borne disease season will be this year because many variables would need to be considered. However, here are some observations we make every year:
- Lyme disease and HGE risk is greatest from mid-May through mid-July, corresponding to the peak feeding period of the nymph stage of the deer tick (Ixodes scapularis) (approximately 85% of reported Lyme disease cases and 66% of HGE cases are exposed during this time). With added incubation time, most HGE cases are diagnosed in late-May through June, and Lyme disease diagnoses peak somewhat later, from late June through early August.
- A smaller number of Lyme disease and HGE cases are reported prior to the above peaks each spring (due to bites from infected adult female deer ticks that come out as soon as the snow melts), and again in the fall (when adult female ticks become active again in mid-September).
- Deer ticks may be infected with multiple pathogens (agents of Lyme disease, HGE, and/or babesiosis), so co-infections in people are possible. During 2000, 8 of 79 (10%) HGE patients were apparently co-infected with Borrelia burgdorferi (the cause of Lyme disease), as they presented with erythema migrans and met the surveillance case definition for Lyme disease.
For further information check out the MDH Lyme Disease Web Page, or 651-201-5414.
2. Rabies Quiz
- Rabies in wildlife is relatively rare compared to the past.
- Postexposure prophylaxis might be appropriate even if a bite, scratch,
or mucous membrane exposure from a bat is not apparent when there is
reasonable probability that such exposure might have occurred.
- A mouse bite often requires postexposure prophylaxis.
- The lack of human cases associated with dog and cat bites in Minnesota
means that the risk is low and prophylaxis is not necessary.
- If you have rabies vaccine but not rabies immune globulin, that provides
sufficient protection in a postexposure prophylaxis situation. Answers:
- False. Rabies in wildlife, especially skunks, raccoons, and bats
has been on the increase since the 1950's.
- True. Examples include any direct contact with a bat, finding
a bat in a room with a previously unattended child, or waking up
to find a bat in your room and you can't rule out a bat bite. Bat
bites may be small and extremely difficult to detect.
- False. Bites from small rodents almost never require prophylaxis
- call us for consultation.
- False. Proper vaccination has reduced but not eliminated rabies
in these animals. We see rabid dogs and cats in Minnesota including
the metropolitan area every year.
- False. Rabies has occasionally occurred in humans when key elements of postexposure prophylaxis are omitted. When postexposure prophylaxis is given, both rabies immune globulin and the rabies vaccine series must be given.
- False. Rabies in wildlife, especially skunks, raccoons, and bats has been on the increase since the 1950's.
At this time of the year we always experience an increase in the number of calls requesting advice regarding rabies prophylaxis. We maintain a 24-hour call service for health care providers and veterinarians for such issues (651-201-5414).
3. Gastroenteritis Outbreak
On May 7, we were alerted of a possible outbreak of gastroenteritis among attendees of an international convention of approximately 280 food stylists held at a Minneapolis hotel April 29-May 2 (we don't make this stuff up - we just report it). Attendees were from many different states and several countries. Preliminary reports were consistent with a bacterial gastroenteritis. On May 8 the Kansas Department of Health reported to us a confirmed case of salmonellosis in a convention attendee. On May 9, the Wisconsin Department of Health reported a confirmed case of Salmonella Enteritidis in an attendee. Several case-patients have been hospitalized. Early environmental investigation revealed that attendees were served Eggs Benedict with Hollandaise sauce prepared with raw eggs (hence the animal connection). The preliminary epidemiologic investigation and data analyses have shown an association between illness and eating the Eggs Benedict.
4. Foot and Mouth Disease - Report from the Front
Dr. Heidi Kassenborg of our bioterrorism epidemiology staff was granted a leave of absence three weeks ago to go to the United Kingdom to serve as a veterinarian on the front lines in the foot and mouth disease crisis. She reported to us that she diagnosed her first cases of foot and mouth disease in sheep on a farm in rural southwestern England on May 4, resulting in the slaughter of approximately 250 ewes, 300 sheep, and 160 cattle the next day on that farm and contiguous farms. The incidence of foot and mouth disease appears to be declining in the U.K. but Heidi reports it's still too early to tell. Meanwhile, we remain vigilant in the U.S. and Minnesota to keep the disease from entering (see March 14 Bug Bytes issue for details). Heidi's experience will be invaluable to us in many ways.
Bug Bytes is a combined effort of the Infectious Disease Epidemiology, Prevention and Control Division and the Public Health Laboratory Division of MDH. We provide Bug Bytes as a way to say THANK YOU to the infection control professionals, laboratorians, local public health professionals, and health care providers who assist us.
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