History and exam

Key diagnostic factors

common

presence of risk factors

Key risk factors include tick bite or exposure, male sex, and immunosuppression. Infection tends to be more severe in patients over 60 years of age.[16][61][62][63]

fever

One of the most common constitutional symptoms and generally has an abrupt onset.

May or may not be associated with rigors.

Lasts for 10 to 14 days without antibiotic treatment.​[16][61][62][63][69][80]​​[99][100]​​​

Present in 99% of human monocytotropic/monocytic ehrlichiosis (HME) cases and 93% of human granulocytotropic/granulocytic anaplasmosis (HGA) cases. Unknown occurrence in human ewingii ehrlichiosis (HEE).​[16][61][62][63][66][69][70][72][80][100][101]

headache

One of the most common constitutional symptoms and may be severe.

Present in 64% of human monocytotropic/monocytic ehrlichiosis (HME) cases and 76% of human granulocytotropic/granulocytic anaplasmosis (HGA) cases. Unknown occurrence in human ewingii ehrlichiosis (HEE).​[16][61][62][63][66][69][70][72][80][100][101]

malaise

One of the most common constitutional symptoms.

Persists for months after acute disease.

Present in 53% of human monocytotropic/monocytic ehrlichiosis (HME) cases and 94% of human granulocytotropic/granulocytic anaplasmosis (HGA) cases. Unknown occurrence in human ewingii ehrlichiosis (HEE).​[16][61][62][63][66][69][70][72][80][100][101]

myalgia

One of the most common constitutional symptoms.

Present in 53% of human monocytotropic/monocytic ehrlichiosis (HME) cases and 77% of human granulocytotropic/granulocytic anaplasmosis (HGA) cases. Unknown occurrence in human ewingii ehrlichiosis (HEE).​[16][61][62][63][66][69][70][72][80][100][101]

arthralgia

One of the most common constitutional symptoms.

Present in 43% of human monocytotropic/monocytic ehrlichiosis (HME) cases and 46% of human granulocytotropic/granulocytic anaplasmosis (HGA) cases. Unknown occurrence in human ewingii ehrlichiosis (HEE).​[16][61][62][63][66][69][70][72][80][100][101]

nausea

One of the most common constitutional symptoms.

Present in 48% of human monocytotropic/monocytic ehrlichiosis (HME) cases and 38% of human granulocytotropic/granulocytic anaplasmosis (HGA) cases. Unknown occurrence in human ewingii ehrlichiosis (HEE).​[16][61][62][63][66][69][70][72][80][100][101]

uncommon

small erythematous lesion with or without necrotic centre

On examination of the skin, a small round erythematous lesion with or without a small necrotic dark centre (eschar) may be seen (tick bite).

[Figure caption and citation for the preceding image starts]: Tick bite at later stage with central necrosis (dark area around tick bite) surrounded by a markedly erythematous areaCourtesy of Lucas Blanton, MD [Citation ends].com.bmj.content.model.Caption@781694fd

non-specific rash

One of the more infrequent constitutional symptoms in adults, but more common in children.

Can be macular, maculopapular, or petechial, and occur anywhere on the body. [Figure caption and citation for the preceding image starts]: Erythematous macular rash involving the lower extremity in a paediatric case of human monocytotropic/monocytic ehrlichiosisCourtesy of Edwin Masters, MD [Citation ends].com.bmj.content.model.Caption@7a4c61e1

Present in 28% (adults) and 67% (children) of human monocytotropic/monocytic ehrlichiosis (HME) cases and 6% of human granulocytotropic/granulocytic anaplasmosis (HGA) cases. Unknown occurrence in human ewingii ehrlichiosis (HEE).​[16][61][62][63][66][69][70][72][80][100][101]

Other diagnostic factors

uncommon

vomiting

One of the more infrequent constitutional symptoms.

Present in 36% of human monocytotropic/monocytic ehrlichiosis (HME) cases and 26% of human granulocytotropic/granulocytic anaplasmosis (HGA) cases. Unknown occurrence in human ewingii ehrlichiosis (HEE).​[16][61][62][63][66][69][70][72][80][100][101]

diarrhoea

One of the more infrequent constitutional symptoms.

Present in 21% of human monocytotropic/monocytic ehrlichiosis (HME) cases and 16% of human granulocytotropic/granulocytic anaplasmosis (HGA) cases. Unknown occurrence in human ewingii ehrlichiosis (HEE).​[16][61][62][63][66][69][70][72][80][100][101]

abdominal pain

One of the more infrequent constitutional symptoms.

Present in 18% of human monocytotropic/monocytic ehrlichiosis (HME) cases. Not reported in human granulocytotropic/granulocytic anaplasmosis (HGA). Unknown occurrence in human ewingii ehrlichiosis (HEE).​[16][61][62][63][66][69][70][72][80][100][101]

cough

One of the more infrequent constitutional symptoms.

Present in 23% of human monocytotropic/monocytic ehrlichiosis (HME) cases and 19% of human granulocytotropic/granulocytic anaplasmosis (HGA) cases. Unknown occurrence in human ewingii ehrlichiosis (HEE).​[16][61][62][63][66][69][70][72][80][100][101]

dyspnoea

One of the more infrequent constitutional symptoms.

Present in 16.5% of human monocytotropic/monocytic ehrlichiosis (HME) cases. Not reported in human granulocytotropic/granulocytic anaplasmosis (HGA). Unknown occurrence in human ewingii ehrlichiosis (HEE).​[16][61][62][63][66][69][70][72][80][100][101]

stiff neck

One of the more infrequent neurological symptoms.

Present in 21% of human granulocytotropic/granulocytic anaplasmosis (HGA) cases. Not reported in human monocytotropic/monocytic ehrlichiosis (HME). Unknown occurrence in human ewingii ehrlichiosis (HEE).​[16][61][62][63][66][69][70][72][80][100][101]

confusion

One of the more infrequent neurological symptoms.

Present in 22.4% of human monocytotropic/monocytic ehrlichiosis (HME) cases and 17% of human granulocytotropic/granulocytic anaplasmosis (HGA) cases. Unknown occurrence in human ewingii ehrlichiosis (HEE).​[16][61][62][63][66][69][70][72][80][100][101]

photophobia

One of the more infrequent neurological symptoms.

Present in 17% of human monocytotropic/monocytic ehrlichiosis (HME) cases. Not reported in human granulocytotropic/granulocytic anaplasmosis (HGA). Unknown occurrence in human ewingii ehrlichiosis (HEE).​[16][61][62][63][66][69][70][72][80][100][101]

stupor

Central nervous system complications are more common in human monocytotropic/monocytic ehrlichiosis (HME).

Present in 4% of HME cases. Not reported in human granulocytotropic/granulocytic anaplasmosis (HGA). Unknown occurrence in human ewingii ehrlichiosis (HEE).​[16][61][62][63][66][69][70][72][80][100][101]

coma

Central nervous system complications are more common in human monocytotropic/monocytic ehrlichiosis (HME).

Present in 4% of HME cases. Not reported in human granulocytotropic/granulocytic anaplasmosis (HGA). Unknown occurrence in human ewingii ehrlichiosis (HEE).​[16][61][62][63][66][69][70][72][80][100][101]

seizures

Central nervous system complications are more common in human monocytotropic/monocytic ehrlichiosis (HME).

Present in 4% of HME cases. Not reported in human granulocytotropic/granulocytic anaplasmosis (HGA). Unknown occurrence in human ewingii ehrlichiosis (HEE).​[16][61][62][63][66][69][70][72][80][100][101]

lymphadenopathy

Rarely seen on physical examination.

Present in 27% of human monocytotropic/monocytic ehrlichiosis (HME) cases. Not reported in human granulocytotropic/granulocytic anaplasmosis (HGA). Unknown occurrence in human ewingii ehrlichiosis (HEE).​[16][61][62][63][66][69][70][72][80][100][101]

jaundice

Rarely seen on physical examination.

Present in 15% of human monocytotropic/monocytic ehrlichiosis (HME) cases. Not reported in human granulocytotropic/granulocytic anaplasmosis (HGA). Unknown occurrence in human ewingii ehrlichiosis (HEE).​[16][61][62][63][66][69][70][72][80][100][101]

hepatomegaly

Rarely seen on physical examination.

More common in children.

Present in 9% (adults) and 25% (children) of human monocytotropic/monocytic ehrlichiosis (HME) cases. Not reported in human granulocytotropic/granulocytic anaplasmosis (HGA). Unknown occurrence in human ewingii ehrlichiosis (HEE).​[16][61][62][63][66][70][72][80][100][101]

splenomegaly

Rarely seen on physical examination.

Present in 9% (adults) and 25% (children) of human monocytotropic/monocytic ehrlichiosis (HME) cases. Not reported in human granulocytotropic/granulocytic anaplasmosis (HGA). Unknown occurrence in human ewingii ehrlichiosis (HEE).​[16][61][62][63][66][69][70][72][80][100][101]

secondary infections

Candidiasis, cytomegalovirus, and aspergillosis may be seen in severe cases of human monocytotropic/monocytic ehrlichiosis (HME) and human granulocytotropic/granulocytic anaplasmosis (HGA).

Risk factors

strong

tick bite/exposure

Ehrlichiosis has a seasonal distribution that coincides with higher tick activity in warmer months (e.g., April through to September in the US), when people tend to spend more time outdoors.

Infections can be seen in other months, albeit with less frequency. Cases outside this period occur in lower latitudes with mild winters.

Human monocytotropic/monocytic ehrlichiosis (HME) occurs mostly across the south central and south-eastern states, although cases have been reported in almost all states.[21]​ Human granulocytotropic/granulocytic anaplasmosis (HGA) occurs mostly across north-eastern states, the Upper Mid-west, and the Pacific North-west.[21]​​

Tick attachment has to last for 24 to 48 hours for disease to occur. Incubation time is 1 to 2 weeks after tick bite. Tick bite does not always result in disease.

Although a strong risk factor, lack of a tick bite history cannot exclude diagnosis in patients with signs, symptoms, and investigation results consistent with tick-borne illness.

immunosuppression

Associated with more severe disease in human monocytotropic/monocytic ehrlichiosis (HME) and human granulocytotropic/granulocytic anaplasmosis (HGA).[57] Most cases of human ewingii ehrlichiosis (HEE) occur in immunosuppressed patients.[4][58][59]

In patients with HIV/AIDS, 70% of cases of HME occurred in patients with CD4+ count <200 cells/microlitre, and infections tend to be more severe with a more frequent risk of complications.[57]​ Sulfonamides used in these patients have been reported to aggravate infection.[60]

Overall case-fatality rates for immunosuppressed patients with any type are about 25%. All reported fatal cases in HIV/AIDS are due to HME.[4][57]​​[58]​​

age over 60 years

Infection tends to be more severe in patients aged over 60 years.[16][61][62][63]

male sex

More common in males due to greater participation in outdoor activities.

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