Ehrlichia canis

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Ehrlichia canis
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Bacteria
Phylum: Pseudomonadota
Class: Alphaproteobacteria
Order: Rickettsiales
Family: Ehrlichiaceae
Genus: Ehrlichia
Species:
E. canis
Binomial name
Ehrlichia canis
(Donatien and Lestoquard 1935) Moshkovski 1945 [1] [2]

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 South), [3] South America, Asia, Africa and recently in the Kimberley region of Australia. [4] [5] First defined in 1935, E. canis emerged in the United States in 1963 and its presence has since been found in all 48 contiguous United States. [3] [6] Reported primarily in dogs, E. canis has also been documented in felines and humans, where it is transferred most commonly via Rhipicephalus sanguineus , the brown dog tick. [3]

Contents

Transmission cycle

The brown dog tick, R. sanguineus, acts as the primary vector of E. canis, transferring the pathogen between hosts during blood meals. Dogs, both domestic and wild, act as reservoir hosts for this pathogen and are the primary hosts of brown dog ticks. Brown dog ticks become carriers of the pathogen when they take a blood meal from a rickessemic dog. Stored in the midgut and salivary glands of an infected tick, E. canis is transferred by the saliva of ticks carrying the pathogen to hosts during blood meals. [3] If infected while in the larval stage, the tick retains the pathogen through the next two life stages and can infect hosts during blood meals in both the nymphal and adult stages in transstadial transmission. [4]

Because the vector of E. canis uses canine species as a primary host, this bacterium is most commonly associated with dogs, but multiple human cases have been reported. [7] Additionally, some cats have been found to have antibodies to E. canis suggesting that it can occasionally infect cats, as well. [8] [9]

Pathogenesis

E. canis is a small, coccus bacterium with a single circular chromosome. Minute in size, E. canis is smaller than the other species in the genus Ehrlichia. [8] [10]

The cell walls of this organism lack peptidoglycans and lipopolysaccharides typically present in at least small amounts in most other Gram-negative bacteria, which is believed to contribute to its ability to resist the immune response of the host. The lack of these two materials reduces the rigidity of the cell wall, allowing the cell wall's exterior to be dynamic, in turn facilitating the E. canis cells’ evasion of antibodies in its host organism's body. [10]

The cells of E. canis lack complex internal structures, which allow the synthesis of sugars and it, in turn, uses amino acids as its source of energy. [10]

Upon introduction, E. canis penetrates the monocytes and macrophages of hosts. Infection may leave a host asymptomatic for months or severe clinical signs may manifest as ehrlichiosis develops. [11]

Diagnosis and treatment

Animals infected with E. canis may experience a combination of signs, including fever, lethargy, weight loss, lymphadenopathy, edema of the appendages, discharge from nose and eyes, and seizures. [4] [6] [11] A low packed cell volume in the blood is a common indicator of the presence of E. canis and a blood smear can be done to determine if morulae are present in leukocytes to definitively diagnose the infection. Because this process is often long and tedious, the presence of antibodies to E. canis in blood can be used to effectively diagnose a patient. These antibodies typically appear within seven days after infection. [4] [6]

E. canis is commonly treated via chemoprophylaxis with doxycycline, a prescription drug used in the treatment of bacterial infections. If caught before the clinical stage, E. canis is almost completely curable, but prolonged presence of the bacteria leads to hemorrhaging, which typically results in the death of the patient. [3]

Although no vaccine is known to be on the market for ehrlichiosis caused by E. canis, extensive research on the use of an attenuated strain of E. canis as an aid in the prevention of E. canis infection is being performed. Preliminary testing has proved that this method may be effective, as clinical signs and the presence of the E. canis bacteria were reduced in Beagle test subjects, but further investigations are necessary before a vaccine can be marketed. [12]

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Ehrlichiosis is a tick-borne disease of dogs usually caused by the rickettsial agent Ehrlichia canis. Ehrlichia canis is the pathogen of animals. Humans can become infected by E. canis and other species after tick exposure. German Shepherd Dogs are thought to be susceptible to a particularly severe form of the disease; other breeds generally have milder clinical signs. Cats can also be infected.

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<i>Dermacentor variabilis</i> Species of tick

Dermacentor variabilis, also known as the American dog tick or wood tick, is a species of tick that is known to carry bacteria responsible for several diseases in humans, including Rocky Mountain spotted fever and tularemia. It is one of the best-known hard ticks. Diseases are spread when it sucks blood from the host. It may take several days for the host to experience symptoms.

<i>Anaplasma phagocytophilum</i> Species of bacterium

Anaplasma 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 also causes the zoonotic disease human granulocytic anaplasmosis.

<span class="mw-page-title-main">Anaplasmosis</span> Medical condition

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<span class="mw-page-title-main">Ehrlichiosis</span> Medical condition

Ehrlichiosis is a tick-borne bacterial infection, caused by bacteria of the family Anaplasmataceae, genera Ehrlichia and Anaplasma. These obligate intracellular bacteria infect and kill white blood cells.

<i>Ehrlichia</i> Genus of bacteria

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.

<i>Amblyomma americanum</i> Species of tick

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<i>Brucella canis</i> Species of bacterium

Brucella canis is a Gram-negative bacterium in the family Brucellaceae that causes brucellosis in dogs and other canids. It is a non-motile short-rod or coccus-shaped organism, and is oxidase, catalase, and urease positive. B. canis causes infertility in both male and female dogs. It can also cause inflammation in the eyes. The hosts of B. canis ranges from domestic animals to foxes and coyotes. It is passed from species to species via genital fluids. Treatments such as spaying, neutering, and long-term antibiotics have been used to combat B. canis. The species was first described in the United States in 1966 where mass abortions of beagles were documented. Brucella canis can be found in both pets and wild animals and lasts the lifespan of the animal it has affected. B. canis has two distinct circular chromosomes that can attribute to horizontal gene transfer.

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<i>Ehrlichia ewingii</i> Species of bacterium

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.

<span class="mw-page-title-main">Human granulocytic anaplasmosis</span> Medical condition

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, including Ixodes scapularis and Ixodes pacificus in North America. These ticks also transmit Lyme disease and other tick-borne diseases.

<i>Rhipicephalus sanguineus</i> Species of species of tick found worldwide

Rhipicephalus sanguineus, commonly called the brown dog tick, kennel tick, or pantropical dog tick, is a species of tick found worldwide, but more commonly in warmer climates. This species is unusual among ticks in that its entire lifecycle can be completed indoors. The brown dog tick is easily recognized by its reddish-brown color, elongated body shape, and hexagonal basis capituli. Adults are 2.28 to 3.18 mm in length and 1.11 to 1.68 mm in width. They do not have ornamentation on their backs.

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 chaffeensis, the bacteria that causes human monocytic ehrlichiosis (HME).

<i>Streptococcus canis</i> Species of bacterium

Streptococcus canis is a group G beta-hemolytic species of Streptococcus. It was first isolated in dogs, giving the bacterium its name. These bacteria are characteristically different from Streptococcus dysgalactiae, which is a human-specific group G species that has a different phenotypic chemical composition. S. canis is important to the skin and mucosal health of cats and dogs, but under certain circumstances, these bacteria can cause opportunistic infections. These infections were known to afflict dogs and cats prior to the formal description of the species in Devriese et al., 1986. However, additional studies revealed cases of infection in other mammal species, including cattle and even humans. Instances of mortality from S. canis in humans are very low with only a few reported cases, while actual instances of infection may be underreported due to mischaracterizations of the bacteria as S. dysgalactiae. This species, in general, is highly susceptible to antibiotics, and plans to develop a vaccine to prevent human infections are currently being considered.

<span class="mw-page-title-main">Ticks of domestic animals</span>

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<i>Neorickettsia risticii</i> Species of bacterium

Neorickettsia risticii, formerly Ehrlichia risticii, is an obligate intracellular gram negative bacteria that typically lives as an endosymbiont to parasitic flatworms, specifically flukes. N. risticii is the known causative agent of equine neorickettsiosis, which gets its name from its discovery near the Potomac River in Maryland and Virginia. N. risticii was first recovered from horses in this region in 1984 but was not recognized as the causative agent of PHF until 1979. Potomac horse fever is currently endemic in the United States but has also been reported with lower frequency in other regions, including Canada, Brazil, Uruguay, and Europe. PHF is a condition that is clinically important for horses since it can cause serious signs such as fever, diarrhea, colic, and laminitis. PHF has a fatality rate of approximately 30%, making this condition one of the concerns for horse owners in endemic regions N. risticii is typically acquired in the middle to late summer near freshwater streams or rivers, as well as on irrigated pastures. This is a seasonal infection because it relies on the ingestion of an arthropod vector, which are more commonly found on pasture in the summer months. Although N. risticii is a well known causative agent for PHF in horses, it may act as a potential pathogen in cats and dogs as well. Not only has N. risticii been successfully cultured from monocytes of dogs and cats, but cats have become clinically ill after experimental infection with the bacteria. In addition, N. risticii has been isolated and cultured from human histiocytic lymphoma cells.

<i>Babesia canis</i> Species of single-celled organism

Babesia canis is a parasite that infects red blood cells and can lead to anemia. This is a species that falls under the overarching genus Babesia. It is transmitted by the brown dog tick and is one of the most common piroplasm infections. The brown dog tick is adapted to warmer climates and is found in both Europe and the United States, especially in shelters and greyhound kennels. In Europe, it is also transmitted by Dermacentor ticks with an increase in infections reported due to people traveling with their pets.

References

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