25.2 Bacterial infections of the circulatory and lymphatic systems  (Page 14/24)

HGA is usually a mild febrile disease that causes flu-like symptoms in immunocompetent patients; however, symptoms are severe enough to require hospitalization in at least 50% of infections and, of those patients, less than 1% will die of HGA. J.S. Bakken et al. “Diagnosis and Management of Tickborne Rickettsial Diseases: Rocky Mountain Spotted Fever, Ehrlichioses, and Anaplasmosis–United States. A Practical Guide for Physicians and Other Health Care and Public Health Professionals.” MMWR Recommendations and Reports 55 no. RR04 (2006):1–27. Small mammals such as white-footed mice, chipmunks, and voles have been identified as reservoirs of A. phagocytophilum , which is transmitted by the bite of an Ixodes tick . Five major virulence factors MOH Key Laboratory of Systems Biology of Pathogens, “Virulence Factors of Pathogenic Bacteria, Anaplasma” 2016. http://www.mgc.ac.cn/cgi-bin/VFs/jsif/main.cgi. Accessed July, 26, 2016. have been reported in Anaplasma ; three are adherence factors and two are factors that allow the pathogen to avoid the human immune response. Diagnostic approaches include locating intracellular microcolonies of Anaplasma through microscopic examination of neutrophils or eosinophils stained with Giemsa or Wright stain, PCR for detection of A. phagocytophilum , and serological tests to detect antibody titers against the pathogens. The primary antibiotic used for treatment is doxycycline .

Ehrlichiosis

Human monocytotropic ehrlichiosis (HME) is a zoonotic tickborne disease caused by the BSL-2, obligate intracellular pathogen Ehrlichia chaffeensis . Currently, the geographic distribution of HME is primarily the eastern half of the US, with a few cases reported in the West, which corresponds with the known geographic distribution of the primary vector, the lone star tick ( Amblyomma americanum ). Symptoms of HME are similar to the flu-like symptoms observed in anaplasmosis, but a rash is more common, with 60% of children and less than 30% of adults developing petechial, macula, and maculopapular rashes. Centers for Disease Control and Prevention. “Ehrlichiosis, Symptoms, Diagnosis, and Treatment.” 2016. https://www.cdc.gov/ehrlichiosis/symptoms/index.html. Accessed July 29, 2016. Virulence factors allow E. chaffeensis to adhere to and infect monocytes, forming intracellular microcolonies in monocytes that are diagnostic for the HME. Diagnosis of HME can be confirmed with PCR and serologic tests. The first-line treatment for adults and children of all ages with HME is doxycycline .

Epidemic typhus

The disease epidemic typhus is caused by Rickettsia prowazekii and is transmitted by body lice, Pediculus humanus . Flying squirrels are animal reservoirs of R. prowazekii in North America and can also be sources of lice capable of transmitting the pathogen. Epidemic typhus is characterized by a high fever and body aches that last for about 2 weeks. A rash develops on the abdomen and chest and radiates to the extremities. Severe cases can result in death from shock or damage to heart and brain tissues. Infected humans are an important reservoir for this bacterium because R. prowazekii is the only Rickettsia that can establish a chronic carrier state in humans.