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Orientia tsutsugamushi (Scrub Typhus)

History The earliest clinical reports of possible scrub typhus date back to the Chinese manual Zhouhofang in 313 bc . In 1810 the association of a febrile illness with mite transmission was made in the Niigata Prefecture in Japan, which led to the first clinical definition of tsutsugamushi fever. Historically, the occurrence of scrub typhus was associated with its dominant presence in Asia, in an area…

Rickettsia typhi (Murine Typhus)

In 1922, Hone first described human infections “closely resembling typhus fever.” Since 1926, when Maxcy successfully identified murine typhus as a distinct clinical and epidemiologic entity, and 1931, when Dyer isolated a new typhus group named Rickettsia from rats and fleas, murine typhus has been recognized as a worldwide zoonotic problem. Often underrecognized and believed to be clinically mild, murine typhus may occur in epidemics or…

Rickettsia prowazekii (Epidemic or Louse-Borne Typhus)

Rickettsia prowazekii is the only rickettsial species that can cause devastating, naturally occurring epidemics capable of killing a substantial proportion of human populations infested with body lice. Epidemics are associated with conditions that prevent bathing and washing of clothes in hot water, such as war and poverty, natural disasters such as earthquakes and floods, displacement of populations, jails, and lack of hygiene. Historical accounts of typhus…

Coxiella burnetii (Q Fever)

Q fever remains an intriguing disease despite being studied for more than 80 years. Molecular diagnostics and genomic analysis are adding to our understanding of the disease. The large outbreak in the Netherlands, other outbreaks, and longitudinal studies from France are changing diagnostic and treatment approaches. Although progress has been made, the name Q fever (“Q” for query) remains appropriate, as many questions remain unanswered. Q…

Rickettsia akari (Rickettsialpox)

Rickettsialpox is a worldwide mite-borne rickettsiosis presenting as a febrile and vesicular eruption. It is caused by Rickettsia akari, associated with mice, and transmitted by its ectoparasite, the mite Liponyssoides sanguineus. Etiology Rickettsia akari is classified among spotted fever group rickettsiae based on antigenic and genetic data. Its genome has a size (1.23 Mb) similar to those of other Rickettsia species but its plasmid content varies, possibly…

Rickettsia rickettsii and Other Spotted Fever Group Rickettsiae (Rocky Mountain Spotted Fever and Other Spotted Fevers)

The spotted fevers comprise a large group of tick-, mite-, and flea-borne zoonotic infections that are caused by closely related rickettsiae. These include Rocky Mountain spotted fever (RMSF), boutonneuse fever, African tick bite fever, North Asian tick typhus, lymphangitis-associated rickettsiosis, Queensland tick typhus, Flinders Island spotted fever, Japanese spotted fever, tick-borne lymphadenopathy, Far Eastern spotted fever, flea-borne spotted fever, and rickettsialpox. Rickettsiae are emerging or reemerging…

Introduction to Rickettsioses, Ehrlichioses, and Anaplasmoses

Bacteriology Originally, all small gram-negative bacteria, associated (or not) with arthropods and strictly or facultatively intracellular, were considered Rickettsiaceae. The advent of 16S ribosomal RNA gene sequencing and phylogeny has deeply challenged this classification. The controversy has centered on how much difference between strains should constitute a subspecies. Among the agreed-upon changes, Orientia was created from an independent branch of its phylum. The Ehrlichia group has…

Genital Mycoplasmas: Mycoplasma genitalium , Mycoplasma hominis , and Ureaplasma Species

Taxonomy and Microbiology The clinically important genital mycoplasmas— Mycoplasma hominis, Mycoplasma genitalium, Ureaplasma urealyticum, and Ureaplasma parvum —belong to the Mollicutes class and Mycoplasmataceae family of bacteria. Mycoplasma spp. and Ureaplasma spp. are the only two genera in this family. In this chapter the trivial term genital mycoplasmas is used to refer to these genera collectively. Ureaplasma spp. are most prominently distinguished from Mycoplasma spp. by…

Mycoplasma pneumoniae and Atypical Pneumonia

Reviewed for currency January, 2020 The concept of atypical pneumonia antedated the start of the antibiotic era. At least as early as World War I it was recognized that “…in the larger number of cases observed in the [military] camps the pneumonia was of an atypical nature. The onset tended to be slower than that of the lobar pneumonia of civil life; the course more prolonged.…

Chlamydia pneumoniae

Chlamydiae are obligate intracellular bacterial pathogens whose entry into mucosal epithelial cells is necessary for intracellular survival and subsequent growth. Chlamydiae cause a variety of diseases in animal species at virtually all phylogenic levels, from amphibians and reptiles to birds and mammals. In 1999, Everett and coworkers reported a taxonomic analysis involving the 16S and 23S ribosomal RNA (rRNA) genes and found that the order Chlamydiales…

Psittacosis (Due to Chlamydia psittaci)

Reviewed for currency January 14, 2021 Psittacosis is a systemic infection that frequently causes pneumonia. Its relationship to bird exposure has been known for more than 100 years. In 1879, Ritter studied an outbreak in Switzerland and called it pneumotyphus. Morange applied the term psittacosis (from the Greek word for parrot) in 1892 after studying cases associated with sick parrots. In 1930, the organism was identified…

Chlamydia trachomatis (Trachoma and Urogenital Infections)

Revised August 2, 2021 Chlamydia trachomatis imposes a tremendous burden on human health because it is one of the most common causes of bacterial infection. Worldwide in 2011, an estimated 21 million people had active trachoma, which is an ocular C. trachomatis infection that is the leading cause of infectious blindness. The World Health Organization (WHO) estimated that in 2016, 1.9 million individuals were blind or…

Prions and Prion Disease of the Central Nervous System (Transmissible Neurodegenerative Diseases)

Reviewed for currency February, 2020 Prions are the transmissible agents of a class of neurodegenerative diseases of humans and other mammals. Prions differ from other infectious agents in that they contain no information-bearing nucleic acid. Rather, they are composed mainly, perhaps only, of abnormal conformations of a normally produced cell surface glycoprotein called the prion protein (PrP). These abnormal conformations of PrP are able to trigger…

Hepatitis E Virus

Revised March 29, 2022 Hepatitis E virus (HEV) is a ribonucleic acid (RNA) virus that causes a viral hepatitis that is indistinguishable from other forms of viral hepatitis. The World Health Organization (WHO) estimates a global incidence of 20 million cases of HEV infection annually, accounting for 3.3% of mortality from viral hepatitis. HEV infection most often results in an acute, self-limited disease that does not…

Astroviruses and Picobirnaviruses

Reviewed for currency February, 2020 Viral gastroenteritis is caused largely by noroviruses and sapoviruses (see Chapter 176 ) and by rotaviruses (see Chapter 150 ). Astroviruses are also established as important causes of gastroenteritis, albeit substantially less frequently than the aforementioned viruses. Picobirnaviruses are more recently described viruses that have a possible, although not yet established, role as agents of gastroenteritis. Astroviruses Virology Classification Astroviruses are…

Noroviruses and Sapoviruses (Caliciviruses)

Reviewed for currency November, 2019 Revised February 20, 2021 Acute infectious gastroenteritis is an exceedingly common and widespread illness throughout the world. Noroviruses are major causes of this illness, which is generally self-limited but can result in hospitalization, mortality in young children in the developing world, and severe illness in elderly and immunocompromised patients. Sapovirus, another calicivirus, and Astrovirus (see Chapter 177 ) also cause gastroenteritis…

Rhinovirus

Rhinoviruses are among the most frequent causes of viral infections in humans. They are the major cause of the common cold and are significant contributors to other upper respiratory syndromes as well as certain lower respiratory illnesses. The term common cold is believed to derive from ancient descriptions of illness in traditional Chinese and Roman sources, in which the illness was believed to be caused by…

Hepatitis A Virus

Hepatitis A is generally an acute, self-limited infection of the liver by an enterically transmitted picornavirus, hepatitis A virus (HAV). Infection may be asymptomatic or result in acute hepatitis. Rarely, fulminant hepatitis can ensue. Although the duration and severity of symptoms vary widely, HAV infections never cause chronic liver disease. The availability of effective vaccines against hepatitis A has markedly affected the epidemiology of hepatitis A…

Parechoviruses

Historical Background The initial two serotypes of the genus Parechovirus were isolated in 1956 from children with diarrhea. On the basis of the scheme used at that time for the classification of the enteroviruses, they were classified as echovirus (E) serotypes 22 (Harris strain) and 23 (Williamson strain). After their classification as enteroviruses, it became evident that they differed from other serotypes within the genus. Their…

Coxsackieviruses, Echoviruses, and Numbered Enteroviruses (EV-A71, EVD-68, EVD-70)

This chapter covers human disease caused by the group A coxsackieviruses (CVs), group B CVs, echoviruses (Es), and the numbered enteroviruses (EVs), which are distributed among four species, EV-A to EV-D, of the genus Enterovirus. Viral diseases caused by the closely related and newly designated genus Parechovirus , of the Picornaviridae, are discussed in Chapter 173 . These viruses have many physical, epidemiologic, and pathogenetic characteristics…