Ehrlichiosis is a tick-borne bacterial infection, caused by bacteria of the family

Anaplasmataceae The Ehrlichiaceae are a family of bacteria, included in the order Rickettsiales The Rickettsiales, informally called rickettsias, are an order of small Alphaproteobacteria. They are obligate intracellular parasites, and some are notable patho ...

, genera ''

Ehrlichia ''Ehrlichia'' is a genus of Rickettsiales bacteria that are transmitted to vertebrates by ticks. These bacteria cause the disease ehrlichiosis, which is considered zoonotic, because the main reservoirs for the disease are animals. ''Ehrlichia'' ...

'' and ''

Anaplasma ''Anaplasma'' is a genus of bacteria of the alphaproteobacterial order Rickettsiales, family Anaplasmataceae. ''Anaplasma'' species reside in host blood cells and lead to the disease anaplasmosis. The disease most commonly occurs in areas where ...

''. These obligate intracellular

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...

infect and kill

white blood cell White blood cells, also called leukocytes or leucocytes, are the cell (biology), cells of the immune system that are involved in protecting the body against both infectious disease and foreign invaders. All white blood cells are produced and de ...

s. The average reported annual incidence is on the order of 2.3 cases per million people.

Types

Six (see note below) species have been shown to cause human infection: * ''

Anaplasma phagocytophilum ''Anaplasma phagocytophilum'' (formerly ''Ehrlichia phagocytophilum'') is a Gram-negative bacterium that is unusual in its tropism to neutrophils. It causes anaplasmosis in sheep and cattle, also known as tick-borne fever and pasture fever, and ...

'' causes

human granulocytic anaplasmosis Human granulocytic anaplasmosis (HGA) is a tick-borne, infectious disease caused by ''Anaplasma phagocytophilum'', an obligate intracellular bacterium that is typically transmitted to humans by ticks of the '' Ixodes ricinus'' species complex, i ...

. ''A. phagocytophilum'' is endemic to New England and the north-central and Pacific regions of the United States. * ''

Ehrlichia ewingii ''Ehrlichia ewingii'' is a species of rickettsiales bacteria. It has recently been associated with human infection, and can be detected via PCR serological testing. The name ''Ehrlichia ewingii'' was proposed in 1992. T ...

'' causes

human ewingii ehrlichiosis ''Ehrlichiosis ewingii'' infection is an infectious disease caused by an intracellular bacteria, ''Ehrlichia ewingii''. The infection is transmitted to humans by the tick, ''Amblyomma americanum''. This tick can also transmit ''Ehrlichia chaffeens ...

. ''E. ewingii'' primarily infects deer and dogs (see

Ehrlichiosis (canine) Ehrlichiosis (; also known as canine rickettsiosis, canine hemorrhagic fever, canine typhus, tracker dog disease, and tropical canine pancytopenia) is a tick-borne disease of dogs usually caused by the rickettsial agent '' Ehrlichia canis''. ''Ehr ...

). ''E. ewingii'' is most common in the south-central and southeastern states. * ''

Ehrlichia chaffeensis ''Ehrlichia chaffeensis'' is an obligate intracellular, Gram-negative species of Rickettsiales bacteria. It is a zoonotic pathogen transmitted to humans by the Amblyomma americanum, lone star tick (''Amblyomma americanum''). It is the causative ...

'' causes

human monocytic ehrlichiosis Human monocytotropic ehrlichiosis is a form of ehrlichiosis associated with ''Ehrlichia chaffeensis''. This bacterium is an obligate intracellular pathogen affecting monocytes and macrophages. Symptom and signs The most common symptoms are fever, ...

. ''E. chaffeensis'' is most common in the south-central and southeastern states. * ''

Ehrlichia canis ''Ehrlichia canis'' is an obligate intracellular bacterium that acts as the causative agent of ehrlichiosis, a disease most commonly affecting canine species. This pathogen is present throughout the United States (but is most prominent in the So ...

'' * '' Neorickettsia sennetsu'' *''

Ehrlichia muris ''Ehrlichia muris'' is a species of pathogenic bacteria first isolated from mice, with type strain AS145T. Its genome has been sequenced. References Further reading * * External linksLPSN*WISC entry Ixodes scapularis

The latter three infections are not well studied. Ehrlichia muris eauclairensis was recently discovered and has low reporting numbers due to the fact that it is relatively new and because its symptoms are very similar to the symptoms caused by other Ehrlichia bacteria. In 2008, human infection by a

Panola Mountain Panola Mountain is a granite monadnock near Stockbridge on the boundary between Henry County and Rockdale County, Georgia. The peak is above sea level, rising above the South River. The South River marks the boundary between Henry, Rockdale ...

(in Georgia, USA) ''Ehrlichia'' species was reported. On August 3, 2011, infection by a yet-unnamed bacterium in the genus ''Ehrlichia'' was reported, carried by deer ticks and causing flu-like symptoms in at least 25 people in

Minnesota Minnesota () is a state in the upper midwestern region of the United States. It is the 12th largest U.S. state in area and the 22nd most populous, with over 5.75 million residents. Minnesota is home to western prairies, now given over to ...

and

Wisconsin Wisconsin () is a state in the upper Midwestern United States. Wisconsin is the 25th-largest state by total area and the 20th-most populous. It is bordered by Minnesota to the west, Iowa to the southwest, Illinois to the south, Lake M ...

. Until then, human ehrlichiosis was thought to be very rare or absent in both states. The new species, which is genetically very similar to an ''Ehrlichia'' species found in

Eastern Europe Eastern Europe is a subregion of the Europe, European continent. As a largely ambiguous term, it has a wide range of geopolitical, geographical, ethnic, cultural, and socio-economic connotations. The vast majority of the region is covered by Russ ...

and

Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...

called ''E. muris'', was identified at a

Mayo Clinic The Mayo Clinic () is a nonprofit American academic medical center focused on integrated health care, education, and research. It employs over 4,500 physicians and scientists, along with another 58,400 administrative and allied health staff, ...

Health System hospital in Eau Claire. ''Ehrlichia'' species are transported between cells through the host-cell

filopodia Filopodia (singular filopodium) are slender cytoplasmic projections that extend beyond the leading edge of lamellipodia in migrating cells. Within the lamellipodium, actin ribs are known as ''microspikes'', and when they extend beyond the lame ...

during the initial stages of infection; whereas, in the final stages of infection, the pathogen ruptures the host cell membrane.

Signs and symptoms

Specific symptoms include fever, chills, severe headaches, muscle aches, nausea, vomiting, diarrhea, loss of appetite, confusion, and a splotchy or pinpoint rash. More severe symptoms include brain or nervous system damage, respiratory failure, uncontrollable bleeding, organ failure, and death. Ehrlichiosis can also blunt the immune system by suppressing production of

TNF-alpha Tumor necrosis factor (TNF, cachexin, or cachectin; formerly known as tumor necrosis factor alpha or TNF-α) is an adipokine and a cytokine. TNF is a member of the TNF superfamily, which consists of various transmembrane proteins with a homolog ...

, which may lead to opportunistic infections such as

candidiasis Candidiasis is a fungal infection due to any type of '' Candida'' (a type of yeast). When it affects the mouth, in some countries it is commonly called thrush. Signs and symptoms include white patches on the tongue or other areas of the mouth ...

. Most of the signs and symptoms of ehrlichiosis can likely be ascribed to the immune dysregulation that it causes. A "

toxic shock Toxic shock syndrome (TSS) is a condition caused by bacterial toxins. Symptoms may include fever, rash, skin peeling, and low blood pressure. There may also be symptoms related to the specific underlying infection such as mastitis, osteomy ...

-like" syndrome is seen in some severe cases of ehrlichiosis. Some cases can present with

purpura Purpura () is a condition of red or purple discolored spots on the skin that do not blanch on applying pressure. The spots are caused by bleeding underneath the skin secondary to platelet disorders, vascular disorders, coagulation disorders, ...

and in one such case, the organisms were present in such overwhelming numbers that in 1991, Dr. Aileen Marty of the AFIP was able to demonstrate the bacteria in human tissues using standard stains, and later proved that the organisms were indeed ''Ehrlichia'' using immunoperoxidase stains. Experiments in mouse models further support this hypothesis, as mice lacking TNF-alpha I/II receptors are resistant to liver injury caused by ''Ehrlichia'' infection. About 3% of human monocytic ehrlichiosis cases result in death; however, these deaths occur "most commonly in immunosuppressed individuals who develop respiratory distress syndrome,

hepatitis Hepatitis is inflammation of the liver tissue. Some people or animals with hepatitis have no symptoms, whereas others develop yellow discoloration of the skin and whites of the eyes (jaundice), poor appetite, vomiting, tiredness, abdominal pa ...

, or opportunistic

nosocomial infection A hospital-acquired infection, also known as a nosocomial infection (from the Greek , meaning "hospital"), is an infection that is acquired in a hospital or other health care facility. To emphasize both hospital and nonhospital settings, it is so ...

s."

Prevention

No human vaccine is available for ehrlichiosis. Tick control is the main preventive measure against the disease. However, in late 2012, a breakthrough in the prevention of canine monocytic ehrlichiosis was announced when a vaccine was accidentally discovered by Prof. Shimon Harrus, Dean of the

Hebrew University of Jerusalem The Hebrew University of Jerusalem (HUJI; he, הַאוּנִיבֶרְסִיטָה הַעִבְרִית בִּירוּשָׁלַיִם) is a public research university based in Jerusalem, Israel. Co-founded by Albert Einstein and Dr. Chaim Weiz ...

's Koret School of Veterinary Medicine. Measures of tick bite prevention include staying out of tall grassy areas that ticks tend to live in, treating clothes and gear that a tick could jump on, using EPA approved bug repellent, tick checks for all humans, animals, and gear that potentially came into contact with a tick, and showering soon after being in an area that ticks might also be in.

Treatment

Doxycycline Doxycycline is a broad-spectrum tetracycline class antibiotic used in the treatment of infections caused by bacteria and certain parasites. It is used to treat bacterial pneumonia, acne, chlamydia infections, Lyme disease, cholera, typhus, an ...

and

minocycline Minocycline, sold under the brand name Minocin among others, is a tetracycline antibiotic medication used to treat a number of bacterial infections such as pneumonia. It is generally less preferred than the tetracycline doxycycline. It is also ...

are the medications of choice. For people allergic to

antibiotic An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting bacterial infections, and antibiotic medications are widely used in the treatment and prevention of ...

s of the

tetracycline Tetracycline, sold under various brand names, is an oral antibiotic in the tetracyclines family of medications, used to treat a number of infections, including Acne vulgaris, acne, cholera, brucellosis, plague (disease), plague, malaria, and sy ...

class,

rifampin Rifampicin, also known as rifampin, is an ansamycin antibiotic used to treat several types of bacterial infections, including tuberculosis (TB), ''Mycobacterium avium'' complex, leprosy, and Legionnaires’ disease. It is almost always used tog ...

is an alternative. Early clinical experience suggested that

chloramphenicol Chloramphenicol is an antibiotic useful for the treatment of a number of bacterial infections. This includes use as an eye ointment to treat conjunctivitis. By mouth or by injection into a vein, it is used to treat meningitis, plague, cholera, a ...

may also be effective, but'' in vitro'' susceptibility testing revealed resistance.

Epidemiology

Ehrlichiosis is a nationally notifiable disease in the United States. Cases have been reported in every month of the year, but most cases are reported during April–September.Dahlgren FS, Heitman KN, Drexler NA, Massung RF, Behravesh CB
"Human granulocytic anaplasmosis in the United States from 2008 to 2012: a summary of national surveillance data"
Am J Trop Med Hyg 2015;93:66–72. Nichols KH, Dahlgren FS, Drexler NA, Massung RF, Behravesh CB. Increasing incidence of ehrlichiosis in the United States: a summary of national surveillance of ''Ehrlichia chaffeensis'' and ''Ehrlichia ewingii'' infections in the United States, 2008–2012. Am J Trop Med Hyg 2016;94:52–60. These months are also the peak months for tick activity in the United States. The majority of cases of Ehrlichiosis tend to be in the United States. The states affected most include "the southeastern and south-central United States, from the East Coast extending westward to Texas." Since the first case of Ehrlichiosis was reported in 2000, cases reported to the CDC have increased, for example, in 2000, 200 cases were reported and in 2019, 2,093 cases were reported. Fortunately, the "proportion of ehrlichiosis patients that died as a result of infection" has gone down since 2000. From 2008 to 2012, the average yearly incidence of ehrlichiosis was 3.2 cases per million persons. This is more than twice the estimated incidence for 2000–2007. The incidence rate increases with age, with the ages of 60–69 years being the highest age-specific years. Children less than 10 years and adults aged 70 years and older have the highest case-fatality rates. A documented higher risk of death exists among persons who are immunosuppressed.

References

External links

* Aayushi Pratap
Dog ticks may get more of a taste for human blood as the climate changes
On: ScienceNews. November 30, 2020. {{Gram-negative bacterial diseases Bacterium-related cutaneous conditions Tick-borne diseases

Types

Signs and symptoms

Prevention

Treatment

Epidemiology

See also

References

External links