Rocky Mountain spotted fever is a tick-borne disease caused by the organism Rickettsia rickettsii. It is specifically a bacterial infection spread by the bite of an infected tick. Rocky Mountain spotted fever can be deadly if not treated early. It is spread by several species of ticks in the United States, including the American dog tick, the Rocky Mountain wood tick, and, in parts of …
Venice Forbes Disease in History September 24, 2021 which is also a typhus victim, seldom surviving the disease's attack. Typhus is only a human and lice disease, with no animal reservoirs known to be involved in the disease cycle. When a louse feeds on the blood of a fevered human, it becomes infected with typhus. Once within the louse's gut, the rickettsiae reproduce in such …
Nov 30, 2021 · Rickettsia is a group of vector-borne organisms that cause acute febrile illnesses throughout the world.[1] While the clinical presentation of rickettsial infection is similar, the causative species and epidemiology can vary depending on the region. It is important to recognize both the typical symptoms and the epidemiology of a given region to correctly diagnose and …
Rickettsial diseases (typhus and spotted fever group rickettsioses, scrub typhus and Q fever) may pose a serious public health problem, namely when they are non-diagnosed or misdiagnosed. Although rickettsiae can be isolated from or detected in …
Tickborne spotted fever rickettsioses are the most frequently reported travel-associated rickettsial infections. Those who go on safari—especially those walking in the bush, game hunters, and ecotourists to southern Africa—are at risk for African tick-bite fever.
Immediate empiric treatment with a tetracycline is recommended for all ages, most commonly doxycycline. Chloramphenicol may be an alternative in some cases, but its use is associated with increased risk of death, particularly from R. rickettsii infection, compared with use of a tetracycline. In some areas, tetracycline-resistant scrub typhus has been reported, and azithromycin may be an effective alternative. Limited clinical experience has shown that A. phagocytophilum and R. africae infections respond to treatment with rifampin, which may be an alternative drug for some pregnant or doxycycline-intolerant patients. Expert advice should be sought if alternative agents are being considered.
Rickettsial infections are caused by multiple bacteria from the order Rickettsiales and genera Rickettsia, Anaplasma, Ehrlichia, Neorickettsia, Neoehrlichia, and Orientia ( Table 4-19 ). Rickettsia spp. are classically divided into the spotted fever group (SFG) and the typhus group, although more recently these have been classified ...
More than 1 million cases occur annually, often in farmers or other occupationally exposed people. Most travel-acquired cases of scrub typhus are reported after visits to rural areas in countries where O. tsutusgamushi is endemic, but urban cases have also been described.
felis are globally distributed, particularly in and around port cities and coastal regions with large rodent populations. Humans exposed to flea-infested cats, dogs, and peridomestic animals while traveling in endemic regions, or who enter or sleep in areas infested with rodents, are at most risk for fleaborne rickettsioses. Murine typhus has been reported among travelers returning from Asia, Africa, and the Mediterranean Basin. Most cases acquired in the United States are reported from Hawaii, California, and Texas.
Rocky Mountain spotted fever is characterized by fever, headache, nausea, and abdominal pain. A rash is commonly reported but eschars are not. Patients with murine or epidemic typhus usually present with a severe but nonspecific febrile illness, and approximately half present with a rash.
Most cases acquired in the United States are reported from Hawaii, California, and Texas. Epidemic typhus caused by R. prowazekii infection is reported rarely among tourists but can occur in communities and in refugee or incarcerated populations where body lice are prevalent. Outbreaks often occur during the colder months.
R. rickettsii, E. chaffeensis, E. ewingii, and A. phagocytophilum have specific and distinct cell tropisms. R. rickettsii infects endothelial cells and more rarely infects underlying smooth muscle cells, where rickettsiae multiply freely in the cytoplasm. The rickettsiae cause a small-vessel vasculitis, resulting in a maculopapular or petechial rash in the majority of patients. Vasculitis occurring in organs (e.g., the brain or lungs) can result in life-threatening complications. R. rickettsii does not stain with the majority of routine histopathologic stains and is not detected by blood smear evaluation because of limited numbers of circulating bacteria. Ehrlichioses and anaplasmosis are characterized by infection of leukocytes, where the causative agents multiply in cytoplasmic membrane-bound vacuoles as microcolonies called morulae. E. chaffeensis most frequently infects monocytes, whereas A. phagocytophilum and E. ewingii demonstrate a predilection for granulocytes. Morulae may be stained with conventional Wright or Giemsa stains and are occasionally observed in leukocytes in smears of peripheral blood, buffy coat preparations, or cerebrospinal fluid. In this context, a routine blood smear can provide a presumptive clue for early diagnosis; however, the visualization of morulae still requires confirmatory testing for Ehrlichia or Anaplasma species by serology, polymerase chain reaction (PCR), or immunostaining methods ( 33 ). The demonstration of morulae is also not sensitive, and a case of ehrlichiosis or anaplasmosis might be missed if the diagnosis relies solely on detection of morulae on blood smears. Although the diagnostic sensitivity of a blood smear is greater for HGA than for HME, blood smears might only be positive in up to 60% of patients with HGA ( 34 ).
In the United States, these diseases include 1) Rocky Mountain spotted fever (RMSF), 2) human monocytotropic (or monocytic) ehrlichiosis (HME), 3) human granulocytotropic (or granulocytic) anaplasmosis (HGA, formerly known as human granulocytotropic ehrlichiosis or HGE) ( 1 ), 4) Ehrlichia ewingii infection, and 5) other emerging TBRD. The reported incidence of these diseases has increased during the previous decade. Despite the availability of low-cost and effective antibiotic therapy, which may be used empirically for suspected cases, TBRD continue to cause severe illness and death in otherwise healthy adults and children. The greatest challenge to clinicians is diagnosing these infections early in their clinical course, when antibiotic therapy is most effective ( 2, 3 ). The majority of patients with TBRD seek medical care within 2--4 days of onset of illness ( 4--7 ). In general, these patients are first evaluated by family practitioners, pediatricians, internists, emergency department (ED) physicians, or physician extenders. Early signs and symptoms of these illnesses are notoriously nonspecific, or they might mimic benign viral illnesses, making diagnosis difficult. For example, even in areas where awareness of RMSF is high, approximately 60%--75% of patients with this TBRD receive an alternate diagnosis on their first visit for medical care ( 8, 9 ). Moreover, the earlier patients seek care in the course of their illness, the more likely an alternate diagnosis will be made ( 4 ). The lack of a specific initial syndrome, however, does not imply that the course of these diseases will be benign.
In the United States, R. rickettsii is transmitted to humans by several tick species. However, the species that transmit R. rickettsii most frequently include the American dog tick ( Dermacentor variabilis; Figure 1) in the eastern, central, and Pacific coastal United States and the Rocky Mountain wood tick ( Dermacentor andersoni; Figure 2) in the western United States. In 2005, the brown dog tick ( Rhipicephalus sanguineus; Figure 3 ), a vector of RMSF in Mexico ( 17 ), was implicated as a vector of this disease in a confined geographic area in Arizona ( 18 ). The cayenne tick ( Amblyomma cajennense; Figure 4) is a common vector for RMSF in Central and South America, and its range extends into the United States in Texas ( 19 ). During 1997--2002, the estimated average annual incidence of RMSF, based on passive surveillance, was 2.2 cases per million persons. More than half (56%) of reported cases of RMSF were from only five states: North Carolina, South Carolina, Tennessee, Oklahoma, and Arkansas (CDC, unpublished data, 2005). However, cases have been reported from each of the contiguous 48 states, except Vermont and Maine ( 10,11 ). Average reported annual incidence of RMSF per 1 million population, based on cases reported to CDC during 1997--2002, has been reported ( Figure 5 ). Incidence varies considerably by geographic area. RMSF is also endemic throughout several countries in Central and South America, including Argentina, Brazil, Columbia, Costa Rica, Mexico, and Panama ( 17,19,20 ). Household clusters of disease and hyperendemic foci of infected ticks have been reported ( 3 ,21 ). Dogs are susceptible to RMSF, and they might frequently develop the disease concurrently with other household members in an endemic focus ( 22,23 ).
Obtaining a complete blood cell count (CBC), comprehensive metabolic panel, and examination of peripheral blood smear are essential when considering a diagnosis of TBRD. The total white blood cell (WBC) count is typically normal in patients with RMSF, but increased numbers of immature bands are generally observed. Thrombocytopenia, mild elevations in hepatic transaminases, and hyponatremia might be observed with RMSF ( 35 ), whereas leukopenia (up to 53% of patients), thrombocytopenia (up to 94% of patients), and modest elevations of liver transaminase levels are particularly suggestive of HME and HGA ( 52,53 ). An inverse relation has been reported between the mean WBC and platelet count and the probability that HGA is the cause of nonspecific fever ( 53 ). Blood smears might be useful in identifying patients with HGA ( 34) or E. ewingii infection. Nonspecific changes in the concentrations of routine laboratory parameters that have been observed for patients infected with E. chaffeensis ( 52) or A. phagocytophilum have been reported ( 53; Table 3 ).
In RMSF, a rash typically appears 2--4 days after onset of fever; however, the majority of patients will seek medical care before this period. For adults and children with RMSF, rash frequently occurs earlier in children than in adults ( 43) and is eventually observed in approximately 90% of children.
In June 2001, a girl aged 5 years was taken to an ED in Missouri with a 3-day history of intermittent fever, headache, mild nausea, and a sore throat. On physical examination, the patient had a fever of 105 ° F (40.6 º C) and a maculopapular rash on her legs, including the soles of her feet.
In mid-August 2003, a male child aged 14 months was taken to a community health clinic in Arizona after 1 day of fever 103.7 ° F (39.8 ° C). On physical examination, the child had a maculopapular rash that involved his palms and soles. On auscultation, abnormal breath sounds were detected in the right lower lung. The parent stated that they had not traveled out of the local area recently. No one else in the family was ill, and the child was up-to-date on vaccinations. Chest radiographic evaluation revealed a possible right lower lobe infiltrate. On the basis of clinical and radiographic findings, pneumonia and roseola infantum were diagnosed. The child was administered an intramuscular injection of ceftriaxone and sent home with a prescription for oral amoxicillin/clavulanate.
Definition. Rickettsial infections (rickettsioses) occur worldwide and are associated with the patient having been bitten by an ectoparasite such as a louse, mite, flea, or tick.
The genus Rickettsia is usually divided into the spotted fever group (SFG), where patients present with fever and spots, and the typhus group (TG). Some scholars also include an ancestral group but this is not yet widely accepted. The SFG consists of many species, about 20 of which can cause human infection.
Rickettsiae and related (rickettsia-like) bacteria (such as Ehrlichia, Anaplasma, and Coxiella burnetii bacteria) are an unusual type of bacteria that cause several similar diseases, including the following: Rocky Mountain spotted fever. Epidemic typhus.
Rickettsial infections and related infections (such as anaplasmosis, ehrlichiosis, and Q fever) are caused by an unusual type of bacteria that can live only inside the cells of another organism.
Doctors use two techniques to make the bacteria easier to detect and identify: 1 In immunofluorescence assays, foreign substances produced by the bacteria (antigens) are labeled with a fluorescent dye. 2 The polymerase chain reaction (PCR) technique is used to increase the amount of the bacteria's DNA, so that the bacteria can be detected more rapidly.
Often, doctors cannot confirm an infection with rickettsiae or rickettsia-like bacteria quickly because these bacteria cannot be identified using commonly available laboratory tests. Special blood tests for these bacteria are not routinely available and take so long to process that people usually need to be treated before test results are available. Doctors base their decision to treat on the person's symptoms and the likelihood of possible exposure.
After treatment, most people with a mild infection noticeably improve in 1 or 2 days, and fever usually disappears in 2 to 3 days. People take the antibiotic for a minimum of 1 week—longer if the fever persists.
Rickettsiae and rickettsia-like bacteria are usually spread to people through the bites of ticks, mites, fleas, or lice that previously fed on an infected animal. Ticks, mites, fleas, and lice are called vectors because they spread (transmit) organisms that cause disease from one host to another. Q fever, caused by Coxiella burnetii, can be spread ...
Antibiotics are usually started without waiting to get the results of tests. Early treatment of rickettsial infections can prevent complications from developing, reduce the risk of dying, and shorten the recovery time.
The rickettsias are a family of microorganisms named for American pathologist Howard T. Ricketts, who died of typhus in 1910 while investigating the spread of the disease. The rickettsias, which range in size from 250 nanometres to more than 1 micrometre and have no cell wall but are surrounded by a cell membrane, cause a group of diseases characterized by fever and a rash. Except for Coxiella burnetii, the cause of Q fever, they are intracellular parasites, most of which are transmitted to humans by an arthropod carrier such as a louse or tick. C. burnetii, however, can survive in milk, sewage, and aerosols and can be transmitted to humans by a tick or by inhalation, causing pneumonia in the latter case. Rickettsial diseases can be treated with antibiotics.
Examples of infectious viruses that originated from animal reservoirs in the mid-20th or early 21st century and went on to cause epidemics or pandemics of disease in humans include ebolaviruses, SARS coronavirus, influenza A H1N1, human immunodeficiency virus ( HIV / AIDS ), and SARS-CoV-2 coronavirus. Load Next Page.
Viruses are visible by electron microscopy; they vary in size from about 25 nanometres for poliovirus to 250 nanometres for smallpox virus.
Scrub typhus is caused by R. tsutsugamushi, but it normal ly parasitizes only rats and mice and other rodents, being carried from one to the other by a small mite, Leptotrombidium (previously known as Trombicula ).
Mycoplasmas and ureaplasmas, which range in size from 150 to 850 nanometres, are among the smallest known free-living microorganisms . They are ubiquitous in nature and capable of causing widespread disease, but the illnesses they produce in humans are generally milder than those caused by bacteria. Diseases due to mycoplasmas and ureaplasmas can be treated with antibiotics.
Diagnosis is established by chest X-rays and blood tests.