Tick-borne infections

Clinical Presentation

• Many of the diseases should be suspected in patients with:
  • Flu-like illness that occurs not in flu season
  • ± cytopenias, ± liver enzyme abnormalities
  • Exposure history (outdoors activities, rats)

Diseases

	Lyme disease	Babesiosis	Anaplasmosis	Ehrlichiosis	RMSF
Pathogen	B. burgdorferi	B. microti	A. phagocytophilum	E. chaffeensis	R. rickettsii
Incubation	2-3 wk	1-4 wk	5-14 d	5-14 d	3-12 d
Tick	Black-legged	Black-legged	Black-legged	Black-legged, Lonestar	American dog
Symptoms	Fever	Fever, HA, n/v/d	Fever, HA	Fever, HA, myalgias, n/v	Fever, HA
Cells	Disseminates	Erythrocytes	Granulocytes	Monocytes	Vascular endothelial
Rash	Erythema migrans	Rare	Rare	Maculopapular (30%)	Maculopapular; Eschar with R. parkeri
Labs	Uncommon	Hemolytic anemia, thrombocytopenia, liver enzymes	Leukopenia, liver enzymes, thrombocytopenia	Leukopenia ± lymphocytosis, liver enzymes, thrombocytopenia	Thrombocytopenia, liver enzymes, hyponatremia
Complications	Carditis, neuro sx, arthritis	DIC, ARDS, CHF, AKI	Opportunistic infections, shock	Seizure, coma, CHF, pericardial effusion, shock	Coma/seizure (30%)
Diagnosis	EM, serology	Microscopy	Serology, ±microscopy	Serology, ±microscopy	Serology, biopsy
Mortality	Rare	3-20%	7-10%	2-5%	8%
Treatment	Doxycycline	Azithromycin, Atovaquone	Doxycycline	Doxycycline	Doxycycline

Ticks

Tick	Distribution	Transmits	Comments
American dog tick (Dermacentor variabilis)	East of the Rockies, and in limited areas in the Pacific coast	Tularemia and RMSF	Highest risk of bites in spring and summer. Sometimes called wood ticks.
Blacklegged tick (Ixodes scapularis)	Across the eastern US and in Ontario	Lyme disease, Anaplasma, B. miyamotoi, ehrlichiosis, babesiosis, and Powassan virus	Highest risk in spring through fall, but can be found any time it's above freezing.
Brown dog tick (Thipicephalus sanguineus)	Worldwide	RMSF	Dogs are the primary host but it can also bite humans.
Gulf Coast tick (Amblyomma maculatum)	Coastal areas along the Guld of Mexico and southern Atlantic	Rickettsia parkeri
Lone Star tick (Amblyomma americanum)	Southeastern and eastern United States	Ehrlichiosis, Heartland virus, tularemia, STARI	Very aggressive tick. Irritation at site does not indicate infection.
Rocky Mountain wood tick (Dermacentor andersoni)	Rocky Mountains and southwestern Canada from elevations of 4,000 to 10,500 feet	RMSF, Colorado tick fever, and tularemia
Western blacklegged tick (Ixodes pacificus)	Pacific coast of the U.S., particularly northern California	Anaplasmosis and Lyme disease

Lone star tick (Amblyomma americanum)

• Where found: Widely distributed in the southeastern and eastern United States.
• Transmits: Ehrlichia chaffeensis and Ehrlichia ewingii (which cause human ehrlichiosis), Heartland virus, tularemia, and STARI.
• Comments: A very aggressive tick that bites humans. The adult female is distinguished by a white dot or “lone star” on her back. Lone star tick saliva can be irritating; redness and discomfort at a bite site does not necessarily indicate an infection. The nymph and adult females most frequently bite humans and transmit disease.

Lone star tick (lone_star_tick.jpg)

Map of the United States showing the approximate distribution of the Lone Star tick. The area affected is the eatern half of the country.

Rocky Mountain wood tick (Dermacentor andersoni)

• Where found: Rocky Mountain states and southwestern Canada from elevations of 4,000 to 10,500 feet.
• Transmits: Rocky Mountain spotted fever, Colorado tick fever, and tularemia.
• Comments: Adult ticks feed primarily on large mammals. Larvae and nymphs feed on small rodents. Adult ticks are primarily associated with pathogen transmission to humans.

Rocky Mountain wood tick (rocky_mountain_wood_tick.jpg)

Map of the United States showing the approximate distribution of the Rocky mountain wood tick. The area effected is the Northwestern part of the country.

Western blacklegged tick (Ixodes pacificus)

• Where found: Along the Pacific coast of the U.S., particularly northern California.
• Transmits: Anaplasmosis and Lyme disease.
• Comments: Nymphs often feed on lizards, as well as other small animals. As a result, rates of infection are usually low (~1%) in adults. Stages most likely to bite humans are nymphs and adult females.

Western blacklegged tick (western_blacklegged_tick.jpg)

Map of the United States showing the approximate distribution of the Western blacklegged tick. The area affected is the western coast.