Ehrlichiosis is a name used to describe several bacterial diseases that affect both animals and humans. They are caused by organisms in the genus Ehrlichia.
Ehrlichia chaffeensis causes human monocytic ehrlichiosis (HME). Ehrlichia ewingii also infects humans. Both are found in Maryland.
Ehrlichiosis is a serious illness that can be fatal if not treated correctly, even in previously healthy people. The diagnosis of ehrlichiosis must be made based on clinical signs and symptoms and can later be confirmed using specialized confirmatory laboratory tests.
If Ehrlichiosis is suspected, health care professionals and the CDC advise to treat it immediately. Treatment should never be delayed pending the receipt of laboratory test results, or be withheld on the basis of an initial negative laboratory result.
Number of Ehrlichiosis cases (from Ehrlichia chaffeensis) reported to CDC by the health departments, 1999-2006.
(Source: CDC National Electronic Telecommunications System for Surveillance (NETSS) data). The number of reported cases of Ehrlichia do not reflect the true numbers.
Ehrlichia HME or HGE (rickettsial diseases related to RMSF) may be fatal, however, milder and chronic forms do exist. Usually Ehrlichiosis symptoms appear within the first two weeks after exposure. Ehrlichia organisms are most often transmitted by the bite of an infected tick.
UPDATE 2018- An Ehrlicia muris like agent has been detected in Ixodes cookei ticks in USA. Previously Ehrlichia muris was found only in Japan and Europe. Of course, as with most tick borne diseases there are no commercial tests designed to detect this infection.
Diagnostic tests based on the detection of antibodies will frequently be negative in the first 7-10 days of illness. For this reason, healthcare providers must use their judgment to treat patients based on clinical suspicion alone. Healthcare providers may find important information in the patient’s history and physical examination that may aid clinical suspicion. (CDC)
Clues such as a low platelet count (thrombocytopenia), low white blood cell count (leukopenia), or elevated liver enzyme levels are helpful predictors of ehrlichiosis, but may not be present in all patients depending on the course of the disease.
Although a positive PCR result is helpful, a negative result does not rule out the diagnosis. It is also important to note that antibodies are not detectable in the first few week of illness in 85% of patients, and a negative test during this time does not rule out ehrlichiosis as a cause of illness. In most cases of ehrlichiosis, the IgG IFA titer is typically low, or “negative".
Antibodies to E. chaffeensis may remain elevated for months or longer after the disease has resolved, or may be detected in persons who were previously exposed to antigenically related organisms.
During the first week of illness a microscopic examination of blood smears (known as a peripheral blood smear) may reveal morulae (microcolonies of ehrlichiae) in the cytoplasm of white blood cells in up to 20% of patients.
The type of blood cell in which morulae are observed may provide insight into the infecting species: E. chaffeensis most commonly infects monocytes, whereas E. ewingii more commonly infect granulocytes. However, the observance of morulae in a particular cell type cannot conclusively identify the infecting species. Culture isolation of Ehrlichia is only available at specialized laboratories; routine hospital blood cultures cannot detect Ehrlichia.
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The following is a list of symptoms commonly seen with Ehrlichiosis, however, it is important to note that the combination of symptoms varies greatly from person to person.
Usually rapid onset- Headaches (sometimes sharp- shooting pain), fevers, chills, myalgias (mild to severe), fatigue, confusion, nausea, vomiting, diarrhea, red eyes (conjunctival injection) and cough are some of the more common symptoms. Ehrlichia infections can be mistaken for the flu in milder cases. In more severe cases it may cause breathing difficulties and bleeding disorders.
Low white blood count and elevated liver enzymes are seen in many cases.
Skin rash is not considered a common feature of ehrlichiosis and should not be used to rule in or rule out an infection. Ehrlichia chaffeensis infection can cause a rash in some children and adults. Rash is not commonly reported in patients infected with Ehrlichia ewingii or the Ehrlichia muris-like organism.
The rash associated with Ehrlichia chaffeensis infection may range from maculopapular to petechial in nature, and is usually not pruritic (itchy). The rash usually spares the face, but in some cases may spread to the palms and soles. A type of rash called erythroderma may develop in some patients.
Erythroderma is a type of rash that resembles a sunburn and consists of widespread reddening of the skin that may peel after several days. Some patients may develop a rash that resembles the rash of Rocky Mountain spotted fever making these two diseases difficult to differentiate on the basis of clinical signs alone.
Doxycycline is the first line treatment for adults and children of all ages:
Adults: 100 mg every 12 hours
Children under 45 kg (100 lbs): 2.2 mg/kg body weight given twice a day
Use of antibiotics other than doxycycline and other tetracyclines is associated with a higher risk of fatal outcome for some rickettsial infections. Doxycycline is most effective at preventing severe complications from developing if it is started early in the course of disease. Therefore, treatment must be based on clinical suspicion alone and should always begin before laboratory results return.
Doses may need to be increased or extended due to the severity or duration of the illness and additional co-infections involved.
In cases of life threatening allergies to doxycycline and in some pregnant patients for whom the clinical course of ehrlichiosis appears mild, physicians may need to consider alternate antibiotics. Although recommended as a second-line therapeutic alternative to treat Rocky Mountain spotted fever (RMSF), chloramphenicol is not recommended for the treatment of either ehrlichiosis or anaplasmosis, as studies have shown a lack of efficacy.
Rifampin appears effective against Ehrlichia in laboratory settings. However, rifampin is not effective in treating RMSF, a disease that may be confused with ehrlichiosis. Healthcare providers should be cautious when exploring treatments other than doxycycline, which is highly effective in treating both.
Other antibiotics, including broad spectrum antibiotics are not considered highly effective against ehrlichiosis, and the use of sulfa drugs during acute illness may worsen the severity of infection.
MARYLAND STUDY
J Med Entomol. 2000 May;37(3):349-56.
Ehrlichia chaffeensis (Rickettsiales: Ehrlichieae) infection in Amblyomma americanum (Acari: Ixodidae) at Aberdeen Proving Ground, Maryland.
Stromdahl EY, Randolph MP, O'Brien JJ, Gutierrez AG.
Entomological Sciences Program, U.S. Army Center for Health Promotion and Preventive Medicine, Aberdeen Proving Ground, MD 21010-5403, USA.
Abstract
Human monocytic ehrlichiosis (HME) is a sometimes fatal, emerging tick-borne disease caused by the bacterium Ehrlichia chaffeensis. It is frequently misdiagnosed because its symptoms mimic those of the flu. Current evidence indicates that Amblyomma americanum (L.), the lone star tick, is the major vector of HME.
To determine if E. chaffeensis is present in ticks at Aberdeen Proving Ground, MD, questing A. americanum ticks were collected from 33 sites. Nucleic acid was extracted from 34 adult and 81 nymphal pools. Sequences diagnostic for E. chaffeensis from three different loci (16S rRNA, 120-kDa protein, and a variable-length polymerase chain reaction [PCR] target, or VLPT) were targeted for amplification by the PCR.
Fifty-two percent of the collection sites yielded pools infected with E. chaffeensis, confirming the presence and widespread distribution of E. chaffeensis at Aberdeen Proving Ground. Analysis with the both the 120-kDa protein primers and the VLPT primers showed that genetic variance exists. A novel combination of variance for the two loci was detected in two tick pools. The pathogenic implications of genetic variation in E. chaffeensis are as yet unknown.
PMID: 15535577 [PubMed - indexed for MEDLINE]
Last Updated- February 2019
Lucy Barnes