Ehrlichiae
http://riki-lb1.vet.ohio-state.edu/ehrlichia/background/characteristic.php
Dept. of Veterinary
Biosciences,
The Ohio State Univ.
1925 Coffey Road
Columbus, OH 43210
Phone: 614-292-5661
Ehrlichiae are small gram-negative pleomorphic cocci that are obligatory intracellular
bacteria. Ehrlichiae replicate in the membrane-bound vacuoles (parasitophorous
vacuoles) in the cytoplasm of a specific type of host cells, chiefly granulocytes or
monocytes. Ehrlichial organisms are vector-borne; they replicate in the tick or the
trematode and are horizontally transmitted from infected cells in vectors to the blood
cells of animals or humans.
Once thought only veterinary pathogens, recently several Ehrlichia spp. have been
recognized as emerging human pathogens in the U.S. Human monocytic ehrlichiosis
(HME), caused by Ehrlichia chaffeensis a new monocytotropic ehrlichia, was discovered
in 1986 and human granulocytic ehrlichiosis (HGE), caused by the HGE agent (newly
named Anaplasma phagocytophila), a new granulocytotropic ehrlichia, was discovered in
1994.
In 1999 another granulocytotropic ehrlichia, E. ewingii which was previously
known as a canine pathogen has been recognized as human pathogen. E. sennetsu
(renamed to Neorickettsia sennetsu) is another monocytotropic Ehrlichia sp. and the first
human pathogen discovered in Japan in the 1950?s and recently found in Malaysia.
HME is a systemic disease characterized by fever, headache, myalgia, anorexia, and
chills, and frequently accompanied with leukopenia, thrombocytopenia, anemia, and
elevations in serum hepatic aminotransferases.
The severity of the disease varies from
asymptomatic seroconversion to death, and severe morbidity is frequently documented.
More than 1,500 probable or confirmed cases of HME have been reported primarily in
the southeastern and south central regions since the original discovery of the disease in
1986.
In certain geographic regions, the incidence exceeds that of Rocky Mountain
spotted fever, most known rickettsial (rickettsia is the closest relative of Ehrlichia spp.
and vector-borne) disease in the U.S. HME has been also reported in Europe and Africa.
E. chaffeensis has been most commonly identified in the Lone Star tick (Amblyomma
americanum), and white-tailed deer are considered to be the major reservoir of E.
chaffeensis.
HGE is characterized by similar clinical signs and laboratory findings as HME. To date
more than 500 cases of HGE have been confirmed in the upper Midwest, northeastern,
and Pacific states. These areas correspond to the Lyme disease-endemic foci. HGE has
been more frequently reported in Europe than HME. The causative agent, Anaplasma
phagocytophila (formerly the HGE agent), is closely related to two previously known
veterinary pathogens, Ehrlichia equi and E. phagocytophila (they are now all belong to
the same species: A. phagocytophila). A. phagocytophila has been found in the deer tick
(Ixodes scapularis) and white-footed mice are considered to be the major reservoir of A.
phagocytophila.
Human coinfection with A. phagocytophila and Borrelia burgdorferi
occurs, presenting a new diagnostic and treatment problem. Clinical signs caused by
infection with another granulocytotropic ehrlichia, E. ewingii are very similar to those of
HGE and HME and patients were discovered due to serologic crossreactivity between E.
chaffeensis and E. ewingii.
Neorickettsia sennetsu (formerlyE. sennetsu) causes Sennetsu ehrlichiosis, an
infectious mononucleosis-like disease (fever, fatigue, general malaise, and
lymphadenopathy). Although the mode of transmission of N. sennetsu is still unproven,
N. sennetsu is genetically and antigenically closely related to known trematode-borne
agents.
Therefore, the trematode is considered to be the reservoir and vector, and the
mode of transmission may be oral, as suspected based on association of cases with the
consumption of raw or under-cooked gray mullet fish which often infected with the
metacercaria. Another potential human ehrlichiosis which is yet to be discovered in the
U.S. is human E. canis infection. E. canis is monocytotropic ehrlichia closely related to
E. chaffeensis.
One year after the initial serologic diagnosis our laboratory isolated an E.
canis-like agent from an asymptomatic person in Venezuela who had slight
thrombocytopenia and lymphocytosis, suggesting possible persistent infection as is
commonly seen in dogs with E. canis infection. E. canis infection of dogs is very
common in the U.S. and throughout the world.
For any of human ehrlichioses, no vaccine exists and the diagnosis is made based on
retrospective seroconversions or PCR analysis. Although doxycycline is generally found
effective in treating ehrlichiosis, delayed initiation of therapy, the presence of underlying
illness, and immunosuppression often lead to severe complications, chronic illness, or
death.
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http://www.niaid.nih.gov/newsroom/focuson/bugborne01/erlich.htm
NIAID
Ehrlichiosis
Ehrlichiosis describes several tick-borne bacterial infections originally known to only
affect dogs and livestock in the United States, although human disease has been reported
in the Far East since the 1950s.
Since the mid-1980s, however, bacteria of the genus,Ehrlichia have increasingly infected humans in the United States. In June 1999, the
Centers for Disease Control and Prevention began listing ehrlichiosis as a reportable
disease; 302 cases were reported in 1999
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http://www.cdc.gov/ncidod/dvrd/ehrlichia/Index.htm
Introduction
Toward the end of the 19th century, scientists began to understand the important
potential for ticks to act as transmitters of disease. In the last decades of the 20th century,
several tick-borne diseases have been recognized in the United States, including
babesiosis, Lyme disease, and ehrlichiosis.
Ehrlichiosis is caused by several bacterial species in the genus Ehrlichia (pronounced
err-lick-ee-uh) which have been recognized since 1935. Over several decades, veterinary
pathogens that caused disease in dogs, cattle, sheep, goats, and horses were identified.
Currently, three species of Ehrlichia in the United States and one in Japan are known to
cause disease in humans; others could be recognized in the future as methods of
detection improve.
In 1953, the first ehrlichial pathogen of humans was identified in Japan. Sennetsu fever,
caused by Ehrlichia sennetsu, is characterized by fever and swollen lymph nodes. The
disease is very rare outside the Far East and Southeast Asia, and most cases have been
reported from western Japan.
In the United States, human diseases caused by Ehrlichia species have been recognized
since the mid-1980s. The ehrlichioses represent a group of clinically similar, yet
epidemiologically and etiologically distinct, diseases caused by Ehrlichia chaffeensis, E.
ewingii, and a bacterium extremely similar or identical to E. phagocytophila. The
remainder of the information on this web page will focus on the types of ehrlichiosis that
occur in the United States.
Human ehrlichiosis due to Ehrlichia chaffeensis was first described in 1987. The disease
occurs primarily in the southeastern and south central regions of the country and is
primarily transmitted by the lone star tick, Amblyomma americanum.
Human granulocytic ehrlichiosis (HGE) represents the second recognized ehrlichial
infection of humans in the United States, and was first described in 1994. The name for
the species that causes HGE has not been formally proposed, but this species is closely
related or identical to the veterinary pathogens Ehrlichia equi and Ehrlichia
phagocytophila. HGE is transmitted by the blacklegged tick (Ixodes scapularis) and the
western blacklegged tick (Ixodes pacificus) in the United States.
Ehrlichia ewingii is the most recently recognized human pathogen. Disease caused by E.
ewingii has been limited to a few patients in Missouri, Oklahoma, and Tennessee, most
of whom have had underlying immunosuppression. The full extent of the geographic
range of this species, its vectors, and its role in human disease is currently under
investigation.
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http://www2.lymenet.org/domino/nl.nsf/bce7787f4c707f10852565e3007b8c95/852a1d9a
13812096852565e30018056f?OpenDocument
Lyme Net Newsletter
Volume: 4
Issue: 09
Date: 28-Jun-96
Is Human Granulocytic Ehrlichiosis (HGE) another Lyme Disease?
A Comparison of Clinical, Laboratory, and Epidemiologic Features -
J. Stephen Dumler, M.D.
FROM THE ABSTRACT:
* Human granulocytic ehrlichiosis (HGE) isx caused by a zoonotic
pathogen in the genus Ehrlichia that is transmitted via the bite of
Ixodes ricinus complex ticks. The causative agent is an obligate
intracellular bacterium. HGE and LB are geographically co-
distributed and a proportion of LB and HGE patients have evidence
of concurrent infection by B. burgdorferi, Babesia microti, or the
HGE agent.
* HGE is characterized as an acute febrile illness with or without
headache, myalgias, gastrointestinal or respiratory symptoms and
signs, CNS involvement, leukopenia, thrombocytopenia, and
elevations in hepatic transaminase levels. The usual presentation
is acute and relatively severe, with life-threatening complications
in 7% and death secondary to opportunistic infections in up to 5%
of patients.
* Persistent infection associated with disease caused by Ehrlichia
species is well documented in animals and is increasingly
recognized in humans.
FROM THE NOTES:
* HGE organism is very closely related to E. equi if it is not the
same organism. It responds rapidly to doxycycline.
* Early HGE is severe 50% +/- requiring hospitalization. Average
hospital stay is 5.5 days.
* Peak incidence is May to July with a secondary peak in the late
fall.
* Most cases have been found in Wisconsin and Minnesota. Westchester
County, NY has also had several cases. Cases have also been
identified to lesser extent in CT, RI, MA, MD, PA, FL, AK, and GA.
* Co-infection varies from area to area from 9% to 21%.
* HGE has been diagnosed in about 100 patients so far - 4 have died.
He feels that fatalities were related to secondary infections from
immune suppression.
* Ehrlichia can cause persistent infection post treatment.
* Co-infection can make Lyme disease worse.
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http://www.angelfire.com/punk/lymedisease/M6.html
EXCERPT-
?In conjunction with the CDC in 1992, I provided stored sera on 22 erythema migrans
patients to be tested for various illnesses, including ehrlichiosis. One of the 22 (4.5%), a
man from Perry County, tested positive for E. chaffeensis on IgG only and had stable
titers on paired sera, indicating exposure.?
from-
Ehrlichiosis Missouri State Medical Association American Medical Association Saint
Francis Medical Center Southeast Missouri Hospital M.A.O.P.S. An update with two
case reports by Edwin J. Masters, M.D.
"Ill-favored ticks ...the foulest and nastiest creatures that be." Pliny the Elder (23-79
A.D.) Natural History
In addition to other tick-borne illnesses such as Rocky Mountain spotted fever, tularemia,
babesiosis, arboviruses, possibly Q fever, Lyme disease and other borrelioses, we now
have two additional recently recognized tick vectored illnesses - monocytic and
granulocytic ehrlichiosis.
In the United States there are two identified clinical diseases in humans caused by
Ehrlichia. The first is human monocytic ehrlichiosis (HME) caused by Ehrlichia
chaffeensis and human granulocytic ehrlichiosis (HGE) probably caused by Ehrlichia
phagocytophila, Ehrlichia equi or a similar organism. (1-3) These are both rapidly
emerging tick borne zoonotic infections that have the potential to cause severe and even
fatal human disease. (2-9) Often the clinical findings are nonspecific and it is thought
that these infections account for a portion of unexplained tick associated febrile illnesses
that previously went undiagnosed. (2)
Human monocytic ehrlichiosis (HME) is caused by E. chaffeensis which was initially
isolated from a patient at Fort Chaffee, Arkansas, (10,11) and resembles Rocky Mountain
spotted fever. (2,12)
The patients frequently have fever, chills, headache, arthralgia,
myalgia, nausea, vomiting, and hematologic abnormalities that can include neutropenia,
thrombocytopenia, lymphopenia, and anemia. Elevation of liver enzymes occurs in most
patients at the time of presentation.(13,14) Human granulocytic ehrlichiosis (HGE) was
more recently discovered and is typically found more in the north central states and also
in the northeast. (1,15,16)
There have been no cases of HGE reported in Missouri or the
lower Midwest.(2) The difference between monocytic ehrlichiosis (HME) caused by E.
chaffeensis and granulocytic ehrlichiosis (HGE) probably caused by an E.
phagocytophila-like organism is as the names imply, the predilection for the organism to
localize within monocytes in HME and granulocytes in HGE.(1,17)
They occasionally
form intraleukocytic inclusion bodies called morulae. (1,4,9,18) The lone star tick
(Amblyomma americanum) has been implicated in the transmission of HME (19,20) and
Ixodes scapularis ticks have been implicated in the transmission of HGE.(1)
E. chaffeensis is not only found in Missouri, but Missouri has reported the most cases of
monocytic ehrlichiosis in the nation since 1988. Missouri, Oklahoma, and Arkansas are
the three states with the highest reported incidence. (13) Previous tick studies published
in 1993 showed E. chaffeensis to be in about 1-3% of lone star ticks tested from four
states, including Missouri. (20) More specifically, some of the positive ticks were from
Bollinger County here in Southeast Missouri. (21)
In conjunction with the CDC in 1992,
I provided stored sera on 22 erythema migrans patients to be tested for various illnesses,
including ehrlichiosis. One of the 22 (4.5%), a man from Perry County, tested positive
for E. chaffeensis on IgG only and had stable titers on paired sera, indicating exposure.
The spectrum of ehrlichiosis ranges from asymptomatic seroconversion (1,22-24)to
marked morbidity (8,19,25,26) and even fatal infection. (2-4,7,8) Thus, it is important
that we be aware of this illness because of its potential severity.
Fichtenbaum et al.
published reports on 9 patients (8 definite, 1 probable) diagnosed with life threatening
monocytic ehrlichiosis that were treated at Washington University in St. Louis. All 8
definite cases had fever, chills, thrombocytopenia, and abnormal liver function tests.
Most had leukopenia and four met the diagnostic criteria for toxic shock syndrome with
two requiring mechanical ventilation. One, a 6 year old previously healthy boy died of
complications of the infection. Significantly, he became ill 12 days after a camping trip
in southeastern Missouri. Because the "diagnosis was not considered by the physician
who first cared for these patients", they concluded "greater awareness is needed to ensure
that proper treatment is initiated early." (5)
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JS Dumler, JS Bakken,"Ehrlichial diseases of humans: emerging tick-borne infections,"
Clinical Infections Diseases, vol. 20, pp. 1102-1110; 1995.
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http://www.riaes.org/resources/ticklab/ehrlich.html
EHRLICHIOSIS
During the past 10 years, two tick-borne diseases caused by Ehrlichia spp. have been
recognized in the United States. Human Monocytic Ehrlichiosis (HME) was first
described in 1986. It is caused by E. chaffeensis, which was only discovered in 1991.
Human Granulocytic Ehrlichiosis (HGE), an alternative form of HME, was recognized as
a new disease in 1993. Its causative agent is still uncertain; however, it is similar to
another Ehrlichia equi described from horses.
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