What are the agents of two groups of diseases almost always transmitted by ticks. These two groups of disease have similar symptoms and low specific (they are easily confused with flu); the Ehrlichioses, and anaplasmosis. These two diseases are much in common are in fact quite different, each of which can in some cases be fatal in the absence of adequate care.

These bacteria (for those which are known) always seem to infect animals in hot blood, except the one that infect fish and at least one of its worms (helminth) parasites. The latter caused human illness (Ehrlichiosis of Japan) which seems to have disappeared with the progress in the monitoring of fish eaten raw.

Bacteria Ehrlichia véchiculées by ticks can vary depending on the biogeographic zones or considered continents;

For example in the man with the United States, the two bacteria implicated in human monocytic ehrlichiosis are:

  • Ehrlichia chaffeensis
  • Ehrlichia ewingii.

They vary according to the case-tank considered and/or according to the vector to which they must be adapted (must be that they are resistant to its immune system, with a CoEvolution with this particular host).

A flu syndrome occurring in any person at risk (i.e. attending forests or wooded areas or animals likely to be carriers of ticks), especially if the symptoms are summer or appear from May to October or do evoke disease. If the patient is immunodeficient diagnosis and treatment must be the fastest possible. A medical information sheet should always accompany the second line collection.

Known species

  • E. canis,
  • E. chaffeensis,
  • E. equi,
  • E. phagocytophila,
  • E. risticii,
  • E. ewingii,
  • E. sennetsu

Other species are classified among the ehrlichiae:

  • E. water,
  • E. bovis,
  • E. ovina,
  • E. the ondiri,


The ehrlichiae were first grouped according to the type of the most commonly infected blood cells (granulocytes, lymphocytes, monocytes, platelets). The diseases they have thus been designated as “granulocytic” or “monocytic”, but this ranking may be misleading because some of the species of Ehrlichia were found in other cells as they are primarily. Of more species genetically very different can infect the same cell (disease while taking the same name; “monocytic” ehrlichiosis or “granulocytic” while the étiolgie is actually different, possibly as the vector or the reservoir species…)

The name or the classification of all or part of these bacteria could in the future change. Anderson and his colleagues have for practical reasons proposed to use the sequence of the 16S rRNA as standard to describe to potential new species in this family.


The Ehrlichia are bacilli gram negative of the family Anaplasmataceae (such as other pathogenic bacteria that are Aegyptianella – Anaplasma – Ehrlichia – Eperythrozoon – Haemobartonella – Neoehrlichia – Neorickettsia – Paranaplasma – Xenohaliotis).

These are obligatory intracellular zoonosezoonotiquess bacteria (it can develop within certain white blood cells of their host). Microscopy, so colorful, they appear as “cocci” (name for bacteria in the form of logs) 1-3 μm in diameter.

In the acute phase of the disease they are pathognomonic “morulae” (which only appear however in 1 to 42% of neutrophils circulating for anaplasmosis (and in monocytes and macrophages for HME).)

In leukocytes, the ehrlichiae divided to form colonies in so-called vacuoles morulae (plural of morula which in latin means Mulberry referring to BlackBerry). The formation of morulae is a feature of any group of pathogenic bacteria and is a major component of disease that they induce.

The bacteria can also be of morulae in phagosomes of macrophages of the spleen, liver, lung, kidney, bone marrow and the cerebrospinal fluid (detected at autopsy).


The bacterium is detected in blood smear (colored) in acute phase of the disease where a morulae are visible. Otherwise, a serological diagnosis must confirm his presence. (test ELISA, PCR…). Serology may not be positive if appropriate antibiotic treatment has been prescribed early (PCR is then diagnosed with certainty). Serology is positive in 100% of the other convalescent and can remain that up to 4 or 5 years after infection.

  • A positive serology does however not necessarily indicate an acute infection (2/3 at least seroconversions are asymptomatic)

In the case of neurological complications, the study of cerebrospinal fluid (CSF) shows a pléocytose with morulae in phagosomes of leukocytes. The immunocytology and PCR also prove the presence of Ehrlichia and Anaplasma in CSF.


The description of the ehrlichia is recent. In humans, the bacterium responsible for the ehrlichiosis in the Japan is the first to have been discovered after the 1953 description of this disease. Of other ehrlichia are then described, in 1987 for human monocytic ehrlichiosis and human ehrlichiosis in 1994 human granulocytic. Is perhaps not all the ehrlichia and we now know that the same bacteria can infect the human and the animal; two other species responsible of ehrlichioses canine have been recently described in humans: Ehrlichia canis and Ehrlichia ewingii.


The ehrlichioses were diseases considered rare until about 1995, but of sero-prevalence studies have since shown that they are growing or that they had been had been underdiagnosed.

An increase is much more plausible (making this an emerging disease, that these increases (actual or apparent) correspond to the areas where pullullent since a few decades, and where other disease emerging ticks were found (including Lyme disease).) Co-infections via ticks are also possible and appear to be frequent in these areas. They induce more severe and chronic clinical forms.

  • in North America, it is shown that it was common with Lyme borreliosis, and any murine babesiosis).

In Europe, studies lack human anaplasmosis but in the co-endémie zone data suggest co-infections with Borrelia, and any Babesia or virus TBEV-EEC.

In some species (horse), the infection confers lasting immunity, in others it is sometimes the case (dog or human), but not always. Apparently cured animals can continue to host the bacterium and a few documented re-infection exist; in the two years following infection with a. phagocytophilum. Only the evolution of serology to conclude total healing.

Chronic forms were recently identified in dogs and humans.

They seem to always fatal in dogs.

Prevalence and frequency of disease

In the United States, the two bacteria in question are most often detected (no doubt by what is looking better, but also because populations of ticks and the reservoir species have strongly increased, focusing in the forests become increasingly fragmented and lack of predators able to play their role of sanitary disposal of animals weakened by infections and heavily parasitized by ticks). the disease is primarily detected spring to autumn and corresponding geographic areas well enough the vector ticks density. The Centre-East of us is especially with the South is and the northeast (zone also the most affected by Lyme disease). The 30-70 years seem much more affected (or better detection?) that the children and young adults.

Life cycle

The ehrlichia can develop in a single organization, but provide their dissemination in a cycle involving several species.

The bacteria mainly develops in a reservoir species which may vary according to the biogeographic zone (it is for example of fallow deer to white tail for the US).

The bacterium is then conveyed by another species (haematophagous as the tick or, in the case of Ehrlichiosis from the Japan that affects patients eating raw fish, by a helminth parasite of fish.)


This is to some extent able to evade the immune system in living in the Interior of cells in this system.


It is to avoid being bitten by ticks.

For bites, note the date and the place of the bite, and the period of discovery and extraction of the tick after the supposed contact… to give this information to the doctor if it is driven to consult. (It can be useful to photograph any skin manifestations (rash, petechiae, stains red..) that could potentially Guide for diagnosis), by affixing a centimetre scale on the skin, or scale an object.

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