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Ehrlichiosis

Updated : February 28, 2024





Background

Ehrlichia is a genus of obligate intracellular gram-negative bacteria which infect humans and other mammals through tick bites.

Symptoms and geographic distribution of Ehrlichia infections are similar to those of rickettsial infections, so it is essential to consider Ehrlichia infection in the diagnosis when evaluating individuals with an illness displaying flu-like symptoms in an endemic region.

Epidemiology

An increase in Ehrlichia diagnoses could be attributed to better identification and the availability of diagnostic tools, as well as an expansion of the Lone Star tick’s territory.

In the US, Ehrlichia chaffeesis causes the majority of infections, while Ehrlichia ewingii is observed less frequently. In the South-Central US, Ehrlichia infections are more in locations where the Lone Star tick is common.

According to data from the CDC, nearly 30% of Ehrlichia infections reported in the US originated in Arkansas, Oklahoma, and Missouri. Ticks are more likely to bite humans during summer, when they are in their nymphal and adult phases of development.

Additionally, infections are most prevalent in the elderly. But it must be considered that children are known to develop milder infections; hence, this demographic may be underrepresented in publications.

Anatomy

Pathophysiology

An infection with Ehrlichia is initiated by intracellular uptake of the organism’s infectious extracellular form, the dense core or elementary body. The dense core/elementary body is subsequently ingested by endocytosis, a process in which the organism duplicates and matures to become a reticulate core or reticulate body and eventually morula before transforming into an dense core/elementary body that exits the infected cell to infect other organisms.

Ehrlichia uses a variety of immune evasion mechanisms, including modulation of cytokine and chemokine responses, the reduction of host pattern recognition receptors, and the suppression of apoptosis, to prevent the infection from spreading.

Infection with Ehrlichia chaffeensis is associated with monocytic cells, such as macrophages and monocytes, and infection with Ehrlichia ewingii is associated with neutrophils.

It is possible for organisms to be found in the lymph nodes, spleen, the peripheral blood, and bone marrow. Rather than from the bacteria itself, the clinical manifestations of these infections seem to arise from the inflammatory response of the host.

Etiology

The two members of the Ehrlichia genus are Ehrlichia chaffeesis and Ehrlichia ewingii; Ehrlichia chaffeesis produces human monocytic ehrlichiosis, and Ehrlichia ewingii causes Ehrlichia ewingii ehrlichiosis.

The Ehrlichia genus also contains Ehrlichia canis and Ehrlichia ruminantium, which are primarily associated with veterinary infections, as well as the recently discovered Ehrlichia muris-like agent (EMLA).

Ehrlichia are intracellular, gram-negative, tick-transmitted organisms capable of multiplying in both the infected host and the tick. In addition to people, cattle, sheep, goats, deer, and rodents are also hosts.

Genetics

Prognostic Factors

When promptly detected and treated early, ehrlichiosis typically responds favorably, with clinical improvement occurring within 24-48 hours.

However, in patients with underlying health issues, severe infection, or in those who encounter a delay in treatment, ehrlichiosis can be severe. Due to this, empiric therapy for suspected ehrlichiosis should be initiated as soon as possible, even before the diagnosis is confirmed.

Clinical History

Physical Examination

Age group

Associated comorbidity

Associated activity

Acuity of presentation

Differential Diagnoses

Laboratory Studies

Imaging Studies

Procedures

Histologic Findings

Staging

Treatment Paradigm

by Stage

by Modality

Chemotherapy

Radiation Therapy

Surgical Interventions

Hormone Therapy

Immunotherapy

Hyperthermia

Photodynamic Therapy

Stem Cell Transplant

Targeted Therapy

Palliative Care

Medication

Media Gallary

References

https://www.ncbi.nlm.nih.gov/books/NBK441966/

Ehrlichiosis

Updated : February 28, 2024




Ehrlichia is a genus of obligate intracellular gram-negative bacteria which infect humans and other mammals through tick bites.

Symptoms and geographic distribution of Ehrlichia infections are similar to those of rickettsial infections, so it is essential to consider Ehrlichia infection in the diagnosis when evaluating individuals with an illness displaying flu-like symptoms in an endemic region.

An increase in Ehrlichia diagnoses could be attributed to better identification and the availability of diagnostic tools, as well as an expansion of the Lone Star tick’s territory.

In the US, Ehrlichia chaffeesis causes the majority of infections, while Ehrlichia ewingii is observed less frequently. In the South-Central US, Ehrlichia infections are more in locations where the Lone Star tick is common.

According to data from the CDC, nearly 30% of Ehrlichia infections reported in the US originated in Arkansas, Oklahoma, and Missouri. Ticks are more likely to bite humans during summer, when they are in their nymphal and adult phases of development.

Additionally, infections are most prevalent in the elderly. But it must be considered that children are known to develop milder infections; hence, this demographic may be underrepresented in publications.

An infection with Ehrlichia is initiated by intracellular uptake of the organism’s infectious extracellular form, the dense core or elementary body. The dense core/elementary body is subsequently ingested by endocytosis, a process in which the organism duplicates and matures to become a reticulate core or reticulate body and eventually morula before transforming into an dense core/elementary body that exits the infected cell to infect other organisms.

Ehrlichia uses a variety of immune evasion mechanisms, including modulation of cytokine and chemokine responses, the reduction of host pattern recognition receptors, and the suppression of apoptosis, to prevent the infection from spreading.

Infection with Ehrlichia chaffeensis is associated with monocytic cells, such as macrophages and monocytes, and infection with Ehrlichia ewingii is associated with neutrophils.

It is possible for organisms to be found in the lymph nodes, spleen, the peripheral blood, and bone marrow. Rather than from the bacteria itself, the clinical manifestations of these infections seem to arise from the inflammatory response of the host.

The two members of the Ehrlichia genus are Ehrlichia chaffeesis and Ehrlichia ewingii; Ehrlichia chaffeesis produces human monocytic ehrlichiosis, and Ehrlichia ewingii causes Ehrlichia ewingii ehrlichiosis.

The Ehrlichia genus also contains Ehrlichia canis and Ehrlichia ruminantium, which are primarily associated with veterinary infections, as well as the recently discovered Ehrlichia muris-like agent (EMLA).

Ehrlichia are intracellular, gram-negative, tick-transmitted organisms capable of multiplying in both the infected host and the tick. In addition to people, cattle, sheep, goats, deer, and rodents are also hosts.

When promptly detected and treated early, ehrlichiosis typically responds favorably, with clinical improvement occurring within 24-48 hours.

However, in patients with underlying health issues, severe infection, or in those who encounter a delay in treatment, ehrlichiosis can be severe. Due to this, empiric therapy for suspected ehrlichiosis should be initiated as soon as possible, even before the diagnosis is confirmed.

https://www.ncbi.nlm.nih.gov/books/NBK441966/