Southern Tick-Associated Rash Illness (STARI) is also known as Masters Disease. STARI is a disease that looks and acts and is treated like Lyme disease.
The causitive agent of STARI is unknown, although some people think the bacterium, Borrellia lonestari, could be the causitive agent, and others think it is another form of Lyme disease.
Symptoms are similar to Lyme disease and can include a rash that looks like the bull's eye rash of Lyme.
There is no generally accepted test for STARI at this time.
It is often found in the South and Midwest where Amblyomma americanum (lone star), the tick that transmits STARI, is prevalent. STARI can also be found in the Northern portions of the USA.
The treatment is generally the same as for early Lyme disease, doxycycline.
Rocky Mountain Spotted Tick Fever
Rocky Mountain spotted fever (RMSF) is one of about a dozen spotted fever illnesses found in the Americas, Europe, Asia and Australia. All are caused by bacteria belonging to the genus Rickettsia, a group of pleomorphic (shape-changing), non-motile microbes that replicate only inside of eukaryotic host cells.
It is caused by Rickettsia rickettsii and is transmitted to humans in the United States by two primary tick vectors, the American dog tick (Dermacentor variabilis) and the Rocky Mountain wood tick (Dermacentor andersoni). The brown dog tick, Rhipicephalus sanguineus, has been implicated in some cases of RMSF as well.
Prior to the antibiotic era, Rocky Mountain spotted fever had a mortality rate of up to 30%. Even today, it remains the most common fatal tick-borne disease in the United States; about 3-5% of patients who acquire the infection will die from it. Most of these fatalities occur in the very young and very old and are due to delayed diagnosis and treatment.
The Centers for Disease Control typically receives somewhere between 300-1200 case reports of RMSF each year, although the number has been increasing in recent years. As with many tick-borne infections, there is a seasonal peak in the late spring and summer months, with May, June and July accounting for the most cases. More than 90% of cases are reported from April through September. The disease strikes children disproportionately – peak incidence is in the 5-9 age group, and more than half of all reported cases involve children under 15 years old.
Signs and Symptoms
The usual incubation time between tick bite and symptom onset is 5-10 days. Only about half of patients recall a preceding tick bite. Initial symptoms of Rocky Mountain spotted fever are usually non-specific, consisting of fever, severe headache, myalgias, nausea and loss of appetite. Many patients will present to physicians before the hallmark rash develops, which complicates diagnosis and increases the disease’s potential deadliness.
Rash onset is subtle and usually develops within 2-5 days after symptoms begin. The rickettsiae spread through the lymphatic system, eventually parasitizing and multiplying within endothelial cells. As the host cells die, blood leaks into adjacent tissues, causing both rash and damage to internal organs. Typically, pale spots first appear on the patient’s extremities (hands, feet, forearms and ankles) and eventually spread inward, toward the trunk.
The “classic” RMSF rash, consisting of small, bright red petechial (spotted) lesions, does not usually appear until almost a week after symptom onset. Estimates vary as to its prevalence, with most sources stating that it presents eventually in about half of all RMSF patients. Close to 5% of patients will develop gangrene or skin necrosis, sometimes requiring amputation of the affected extremities.
Around 10-15% of RMSF patients will not develop rash at any stage.
Rocky Mountain spotted fever is multisystemic and potentially severe. Central nervous system manifestations include lethargy and confusion (about 25% of all cases), ataxia (18%), coma (9-10%) and seizures (8%). Other neurologic manifestations include meningitis, cranial neuropathies, deafness, paralysis, spasticity, vertigo, aphasia and photophobia. Ophthalmologic complications can also occur. In addition, RMSF affects the respiratory system, the gastrointestinal system and the renal system. Pulmonary involvement includes edema, pneumonia and respiratory distress syndrome. Microcirculatory vasculitis can lead to myocarditis. Close to 10% of patients develop jaundice during the course of their illness; a similar percentage will produce stools positive for occult blood. Hospitalization is frequently required in advanced cases of RMSF.
African-American males are at particular risk for serious complications of Rocky Mountain spotted fever, as they are genetically more likely to be deficient in glucose-6-phosphate dehydrogenase (G6PD), an enzyme associated with the maintenance of membrane integrity in red blood cells.
While a number of laboratory tests are available for Rocky Mountain spotted fever, none are both rapid and sensitive enough to provide useful diagnostic assistance to the examining physician. As prompt treatment of RMSF is critical to a positive outcome, diagnosis should be made on clinical grounds – i.e., history, epidemiology and clinical exam. This can be challenging, as many patients will not recall the tick bite.
Conventional blood tests can produce results that hint at RMSF. Among the typical findings are hypoanotremia (low sodium), thrombocytopenia, white blood cell abnormalities and/or elevated liver enzymes.
Serological assays are used mostly to confirm the diagnosis after treatment has been initiated. Indirect immunofluorescence assays (IFA) of both IgM and IgG antibodies are most commonly employed, but enzyme linked immunosorbent assays (ELISA) and dot immunoassays are also available. Complement fixation is less sensitive, and less frequently used. Immunostaining of biopsied skin rashes can also be performed and is very rapid; results are available in a few hours. However, the test is only 70% sensitive, so a negative result does not exclude the diagnosis.
Polymerase chain reaction (PCR) assays for R. rickettsii DNA are considered perhaps the most timely and specific test for RMSF overall, but are still not widely available.
Immediate treatment with antibiotics is indicated if RMSF is suspected. Tetracyclines are virtually the only effective class of antibiotics against R. rickettsii, and doxycycline is sometimes recommended even in pediatric cases, although not for pregnant mothers (who are usually treated with chloramphenicol). The usual doxycycline dosage is 200 mg/day in two divided doses. Treatment should be continued until patients have been afebrile for at least three days; the usual treatment course is 7-10 days. Severe cases may require intravenous administration or longer treatment duration.
Bacteria from the genus Ehrlichia have long been recognized as veterinary pathogens, but the first human case of ehrlichiosis was not identified until 1986. Since that year, the number of case reports has grown fairly steadily and currently stands at around 500 per year. Although ehrlichiosis is a nationally reportable disease, reporting is passive, and the true incidence of the Ehrlichia infection is thus assumed to be significantly higher. This suspicion is bolstered by the high rates of background seroprevalence (~12-15%) in endemic areas, a finding that also indicates that many infections are mild and self-limiting or asymptomatic.
Ehrlichia are small, gram-negative bacteria, round or ellipsoidal in shape. They preferentially invade mononuclear phagocytes, such as monocytes and macrophages, and in some cases neutrophils. In all of these cell types they occupy cytoplasmic vacuoles, usually in bacterial microcolonies known as morulae. Ehrlichia cycle in nature between ticks and mammals, and can cause disease in many mammalian species.
The two known primary agents of human ehrlichiosis are E. chaffeensis and E. ewingii. (A third species, E. canis, has recently been found to infect humans, but its significance as a human pathogen is not well understood at this point.) E. chaffeensis targets monocytes and is therefore referred to as the agent of “human monocytic ehrlichiosis” (HME). In contrast, E. ewingii preferentially invades neutrophil granulocytes. In this regard, it resembles the Anaplasma pathogen A. phagocytophilum (see section on Anaplasmosis, below), the agent of human granulocytic anaplasmosis (HGA), although it is genetically and serologically much closer to E. chaffeensis. To avoid confusion with HGA, most researchers prefer to call this disease entity “human ewingii ehrlichiosis.”
E. chaffeensis is known to be transmitted by the Lone star tick, Amblyomma americanum, and white tail deer appear to be its most important natural mammalian reservoir. In the United States, cases of the disease generally track the known distribution of the Lone star tick, occurring throughout the south central, southeastern and mid-Atlantic states, although there have also been scattered case reports in states with no known population of these ticks, such as Montana and Utah. E. ewingii is also thought to be transmitted by Lone star ticks, but less is known about its natural history and enzootic cycle.
Patients are most likely to be infected with Ehrlichia in spring and summer months, though cases occur into autumn as well. Unlike Lyme disease and Rocky Mountain spotted fever, ehrlichiosis strikes older people preferentially, probably due to immunological host factors. However, severe and even fatal cases have also been reported in children and young adults.
Signs and Symptoms
Although E. chaffeensis and E. ewingii invade different host cells, they seem to produce a similar clinical course in humans. Most patients develop symptoms 1-2 weeks after the tick bite, and over 70% will have fever, chills, severe headache and myalgias. Less common symptoms include nausea and vomiting, as well as confusion. A maculopapular rash (easily distinguishable from Rocky Mountain spotted fever) can also occur. As with many other tick-borne diseases, the symptoms are largely non-specific, thus confounding diagnosis.
Although most cases of HME are uncomplicated, it is a potentially serious illness. Hospitalization rates in symptomatic patients are estimated to be 40-50%, and fatalities run in the 2-3% range. At greatest risk are patients with underlying immunosuppression, such as organ transplant recipients or HIV or cancer patients. These patients are also at increased risk for complications in human ewingii ehrlichiosis, but no fatalities have been reported for this infection.
The main complications of ehrlichiosis are prolonged fever, a toxic or septic shock-like syndrome, coagulopathy, adult respiratory distress syndrome, and central nervous system manifestations such as meningoencephalitis, seizures and coma. Peripheral neuropathies, primarily cranial neuritis, are rarer, but have also been reported.
The potential severity of ehrlichial infections makes early diagnosis critical. Common findings on conventional blood tests include leukopenia, thrombocytopenia and elevated serum transaminases, and this triad, which is also found in Rocky Mountain spotted fever, should prompt physicians to seriously consider empiric antibiotic treatment, especially if the patient is from an endemic area and has had recent tick exposure.
From the standpoint of timeliness, the most useful diagnostic test for ehrlichiosis is probably polymerase chain reaction (PCR). Sensitivity has been reported to range between 60-85% for E. chaffeensis; the sensitivity for E. ewingii infections is not known, but PCR is the only definitive diagnostic test for E. ewingii, which has so far never been cultured in vitro. PCR sensitivity is negatively affected by prior antibiotic treatment, so blood samples for PCR testing should be drawn before treatment has been initiated.
Examination of Wright-stained blood smears for the classic ehrlichial morulae colonies is clearly diagnostic for E. chaffeensis if positive in monocytes. This test can be performed rapidly, but is of limited real-world utility due to its lack of sensitivity, which rarely exceeds 25%. As with PCR, prior antibiotic therapy reduces sensitivity.
Culture of E. chaffeensis is possible from either blood or cerebrospinal fluid, but usually takes at least two weeks. Thus, this method is useful only for retrospective confirmation of the diagnosis. Similarly, changes in antibody titers detected by indirect immunofluorescent assay (IFA) during the convalescent phase can buttress the diagnosis, but this testing method is not useful during acute illness, when treatment decisions need to be formulated. Physicians should also be aware that IgG antibodies can remain high for years after the infection, and false positive results have been associated with many other conditions, including several tick-borne diseases (Lyme disease, Rocky Mountain spotted fever, and Q fever).
No treatment studies have been performed for ehrlichiosis, but empiric evidence indicates that tetracyclines are highly effective against both E. chaffeensis and E. ewingii. The most commonly employed regimen is oral doxycycline at a dose of 100 mg every 12 hours, for 5-14 days. (Doxycycline is also recommended for pediatric patients.) In severe cases, intravenous therapy is used or antibiotic treatment is extended. Consensus exists that in all cases, treatment should be continued in all patients for at least 3-5 days after the fever subsides.
In cases where doxycycline is contraindicated, such as pregnancy or allergy, rifampin is usually the alternative choice. Little data exists to support the use of any other antibiotic, as cephalosporins, macrolides, beta lactams and aminoglycosides are all inactive against Ehrlichia organisms in vitro.
The Gram-negative bacterial genus Bartonella currently comprises roughly two dozen identified species, about half of which are known to infect humans. However, the clinical implications of many of these human infections are poorly understood, and it is possible that some of the species are non-pathogenic, at least in immunocompetent people. Until around 15 years ago, only three human diseases were recognized as clearly attributable to Bartonella organisms: cat scratch disease (CSD, also sometimes referred to as cat scratch fever), caused by B. henselae; Carrion's disease, caused by B. bacilliformus (and limited to South America); and trench fever, caused by B. quintana. More recently, however, additional pathogenic Bartonella species have been discovered. The full clinical spectrum of all Bartonella infections remains to be elucidated, but includes conditions as diverse as hepatitis, endocarditis, encephalopathy and meningoencephalitis.
Bartonella are intracellular parasites that generally show preference for erythrocytes and endothelial cells in humans. The organisms are found in a wide range of both wild and domestic mammals, including cattle, rodents, dogs and cats. The various Bartonella species appear to be adapted to specific hosts. Cats are the main reservoir for B. henselae, which causes approximately 20,000 reported cases of cat scratch disease per year in the United States. (As with many reportable diseases, however, the true incidence of CSD is underreported and generally believed to be considerably higher.) Bartonella are also found in numerous arthropods, including fleas (a known vector of CSD), biting flies, lice and ticks.
The evidence for ticks as vectors of Bartonella organisms is circumstantial but fairly strong. Recent studies in both the United States and Europe have found that Ixodes ticks harbor B. henselae in addition to Borrelia, Babesia and Anaplasma organisms; in fact, a 2004 PCR analysis of I. Scapularis ticks in New Jersey discovered that a higher percentage of ticks were infected with B. henselae than any of these other pathogens. In addition, B. henselae has been detected in the spinal fluid of patients co-infected with Borrelia burgdorferi, the agent of Lyme disease. However, the ability of Ixodes ticks to actually transmit B. henselae has not been specifically demonstrated.
Signs and Symptoms
Warthin Starry stain showing B. henselae in cardiac valve of a patient with endocarditis. The bacilli appear as black granulations. Photo courtesy of Pierre Houpikian and Didier Raoult, Unit des Rickettsies, Faculte de Medecine de Marseille, Marseille, France
Cat scratch disease is caused by the transmission of B. henselae to humans by a flea bite or the scratch of a cat. Cat bites may be implicated as well. A week or so after exposure, a papule forms at the transmission site and then usually develops into a pustule. In immunocompetent people, the systemic symptoms of cat scratch disease are usually limited to regional adenopathy, though it can also cause fever and, more rarely, eye disorders, hepatosplenic infection, osteomyelitis, and encephalopathy. Immunocompromised patients, such as those with HIV, can develop more serious manifestations such as endocarditis and bacillary angiomatosis (tumor-like masses caused by the pathological proliferation of blood vessels).
The clinical manifestations of tick-transmitted bartonellosis are essentially unknown. They may resemble cat scratch disease, take other clinical forms, or be benign. It is also unclear if Bartonella co-infection with other tick-transmitted organisms can result in more serious illness; some of the few reported cases of concurrent B. burgdorferi and B. henselae infection in the medical literature appear to suggest this could be the case. Thus, it may be prudent to consider the possibility of Bartonella co-infection in cases of poorly resolving or apparent relapsing Lyme disease.
Given the uncertainties surrounding the presentation and incidence of tick-transmitted bartonellosis, diagnosis cannot be made purely on clinical grounds. Thus, laboratory confirmation of infection assumes increased importance. Serological tests exist for Bartonella infections; most commonly employed are immunofluorescent fluorescent antibody (IFA) assays for both IgM and IgG antibodies. However, cross reactions may occur with antibodies to Q fever, Chlamydia, and certain rickettsial infections. Western blot tests appear to have greater specificity.
False negative serological results can occur in immunocompromised patients.
Bartonella organisms can sometimes be visualized by immunohistochemical staining, although this method of diagnosis is usually reserved for patients with angiomatosis. The DNA of various Bartonella species can also be amplified by PCR in blood, spinal fluid and tissue; given the cross-reactivity of the Bartonella antibody tests, PCR may be the most reliable and useful test for Bartonella infection.
Culture of Bartonella organisms is possible, but the bacteria are generally slow-growing in the laboratory. Thus, this method of diagnosis is of limited usefulness, and is employed mostly in patients with serious and otherwise unexplained disease presentations, such as endocarditis. Studies are currently underway to determine the optimal culture media and methods for Bartonella.
Bartonella is sensitive to many different antibiotics in vitro, but the in vivo performance of these antibiotics in humans and domestic pets does not correlate well with in vitro laboratory studies. Most likely, this stems from two factors: 1) almost all antibiotics are bacteriostatic against Bartonella, rather than bactericidal; and 2) the pathogen is often sequestered in erythrocytes.
Cat scratch disease usually resolves even without treatment, and there is little evidence that antibiotics shorten the duration of the disease. Thus, there is disagreement over whether or not antibiotic treatment is even necessary for uncomplicated CSD. Tick-transmitted Bartonella may be a more serious matter, however, since the possibility of co-infection is always present. In addition, there is general agreement that the presence of B. henselae in cerebrospinal fluid, whatever its origin, warrants treatment.
CSD is most often treated with tetracyclines, macrolides or aminoglycosides. For CNS infection, antibiotics that cross the blood brain barrier are necessary, and combination therapy is usually recommended, as it may have more efficacy. Among the recommended regimens are azithromycin or doxycycline in combination with rifampin, clarithromycin or a fluoroquinolone. The optimal length of therapy has yet to be determined, but most guidelines suggest that treatment should last for at least 4-6 weeks.
Babesia are malaria-like protozoans that parasitize and reproduce within mammalian red blood cells. They have a complex life cycle involving several different stages and physical forms and are maintained in nature primarily via exchange between Ixodes ticks and various mammals. The first Babesia species was discovered in 1888 by Victor Babes, a Hungarian pathologist in whose honor the organisms were subsequently named. Over 100 distinct species have since been identified within the Babesia genus, though only a few of these are currently known to be human pathogens.
Babesiosis has long been recognized as a disease of cattle and other domesticated animals, but the first human case was not described until 1957, when a young Croatian farmer contracted the illness and died some days later of renal insufficiency. In the late 1960s, the first North American cases appeared on Nantucket Island, and the disease is now recognized as an emerging and occasionally serious zoonosis in the United States.
Babesiosis has been reported in North and South America, Europe, and southern and eastern Asia. In the United States, the primary agent of human babesiosis is Babesia microti, which is transmitted by the bite of Ixodes scapularis, the same tick species that vectors Lyme disease. Cases of babesiosis caused by B. microti occur in southern New England and the northern Midwest. Additional cases of babesiosis caused by other species of Babesia occur primarily in the western U.S.; cases from Missouri and Kentucky have also been reported.
Clinically, babesiosis appears to have a wide spectrum of disease severity. Most patients experience a viral-like illness that can last weeks to months but which usually resolves fully. A significant minority of patients are entirely asymptomatic. In patients with a complicating condition, however – such as underlying immunosuppression – the disease course can be severe and potentially fatal. Some species of Babesia, such as B. divergens, appear to be more virulent than others.
Although primarily transmitted by tick bite, babesiosis can also be acquired via blood transfusion and maternal-fetal transmission.
Signs and Symptoms
In immunocompetent patients, symptoms of babesiosis usually begin 1-6 weeks after inoculation and are non-specific. Typical early manifestations include intermittent fevers accompanied by fatigue and malaise, headache, chills, and myalgias. Nausea, vomiting, reduced appetite and depression can also occur. Some patients will develop enlarged livers or spleens. The usual disease course lasts weeks to several months, but some patients take even longer to fully recover. Coinfection with Lyme disease or anaplasmosis may complicate the clinical presentation and predispose the patient to more severe disease.
At the greatest risk for severe babesiosis are the elderly, asplenetic patients, patients with HIV or malignancies, and patients on immunosuppressive medications. In these populations, the disease course is longer and the fatality rate is in the neighborhood of 20%, even with proper antibabesial therapy. The most common serious complication of babesiosis is acute respiratory failure, but heart failure, liver and renal failure, disseminated intravascular coagulation and coma are also well-recognized severe manifestations of babesiosis.
The fact that the early symptoms of babesiosis are largely non-specific makes diagnosis difficult. Nevertheless, physicians encountering a patient from an endemic area who presents with fever and a viral-like illness, especially in the summer months, should be alert to the possibility that babesiosis may be responsible for the patient’s symptoms.
While the physical exam is usually unremarkable, conventional blood tests can produce a pattern that suggests the diagnosis. Because the Babesia organisms cause lysis of red blood cells, patients will frequently develop hemolytic anemia, as well as lymphopenia and thrombocytopenia. Elevated serum lactate dehydrogenase levels are also common, and hyperbilirubinemia and an elevated erythrocyte sedimentation rate may also be present.
If babesiosis is suspected, microscopic examination of blood smears should be pursued. Giemsa or Wright stains are typically used. In early illness, the infection rate of erythrocytes can be less than 1%, so multiple smears over a period of days may be needed to confirm the diagnosis. Babesial DNA can also be detected by polymerase chain reaction (PCR) in cases where smears are negative but the diagnosis is still suspected.
Immunofluorescence (IFA) of IgM and IgG antibodies is sometimes employed to confirm a babesiosis diagnosis. However, antibodies to Babesia organisms can remain high for months or years after clinical resolution of illness, so the test is not a reliable indicator of active infection.
Combination therapy with atovaquone (Mepron) and azithromycin is most commonly recommended for treatment of mild to moderate babesiosis. Treatment is usually continued for 7-10 days. A combination regimen of oral clindamycin and quinine has also been proven effective, but the rate of adverse reactions is significantly higher with this combination, so it is not recommended for treatment of uncomplicated disease.
For patients with severe babesiosis, however, intravenous clindamycin and (oral) quinine is considered the preferred treatment, again for 7-10 days. In patients with underlying immunosuppression and persistent signs and symptoms, studies have shown an association between longer treatment duration and a positive outcome; therefore, treatment of these individuals should be continued for weeks or months until blood smears are negative for at least two weeks. Extended treatment is not considered necessary for immunocompromised patients who respond clinically to the 7-10 day treatment course.
The first case of human anaplasmosis was described in 1990, when a Wisconsin patient developed a severe febrile illness following a tick bite and died two weeks later. Blood smears revealed clusters of bacteria within the patient’s neutrophils, similar to the morulae seen in monocytes with E. chaffeensis infection. However, cultures and serologic tests for E. chaffeensis were negative. Nevertheless, the patient’s clinical course suggested ehrlichiosis of some kind, and when several additional cases of the disease were reported in the northern Midwest in ensuing years, it was posited that a new species of Ehrlichia might be emerging. The new disease was tentatively given the name “human granulocytic ehrlichiosis,” or HGE.
In 1994, DNA sequencing studies revealed that the HGE agent was clearly distinct from E. chaffeensis but essentially identical to two previously known ehrlichial veterinary pathogens, E. equi and E. (Cytoecetes) phagocytophila. Under a new taxonomic scheme since implemented (see Introduction), these three organisms have been united as a single species within a new genus, Anaplasma. The new species is referred to as Anaplasma phagocytophilum, and the disease it causes is now known as human granulocytic anaplasmosis, or HGA.
Like Ehrlichia species, Anaplasma organisms are small, gram-negative and intracellular. A. phagocytophilum targets neutrophils, alters their function in the host, and forms morulae within vacuoles. Most of the damage it causes appears to be related to host inflammatory processes, as there is little evidence of a correlation between the number of organisms and host disease severity.
Anaplasmosis is a global infection, occurring in North America, most of Europe and eastern Asia. Ticks from the Ixodes persulcatus-complex are the vectors: I. scapularis in the northeastern and upper Midwestern regions of the United States; I. pacificus in the Pacific Northwest; I. ricinus in Europe and I. persulcatus in Asia. A. phagocytophilum is maintained in nature by cycling between these ticks and various small mammals, primarily mice and other small rodents. Because Ixodes ticks are also the vectors for Lyme disease, babesiosis and tick-borne encephalitis, Anaplasma coinfection with these other diseases can and does occur in humans.
In the last decade, cases of HGA have outnumbered those of HME in the United States. Similar to HME and human ewingii ehrlichiosis, the median age of patients with HGA is around 50 years old. Over 4000 total cases have been reported in the CDC’s Morbidity and Mortality Weekly since the disease became nationally reportable; as with most tick-borne diseases, the true incidence is suspected to be considerably higher.
Signs and Symptoms
The clinical course of HGA is very wide, ranging from asymptomatic infection to fatal disease. When initial symptoms appear, usually 5-10 days after tick bite, they are largely non-specific and similar to those of HME: fever, chills, severe headache and myalgias. Nausea, cough and arthralgias also occur. Rash is uncommon but has been reported.
Compared with HME, HGA appears less likely to involve the central nervous system, but peripheral neuropathies are more common and can last weeks to months. Among the neurologic findings reported in the medical literature are facial palsy, demyelinating polyneuropathy and brachial plexopathy. Respiratory distress syndrome and a septic or toxic shock-like syndrome have been reported, but appear to be less common than in HME. The overall fatality rate from HGA also seems to be slightly lower than that of HME, with most of the deaths resulting from opportunistic infections (for example, herpes simplex esophagitis, Candida pneumonitis, and pulmonary aspergillosis) in immunocompromised patients.
Standard blood tests in HGA usually reveal findings similar to those seen in HME: leukopenia, thrombocytopenia and liver function abnormalities (elevated transaminases). However, the hematological abnormalities frequently resolve by the second week of symptoms, so their absence should be interpreted in that context if patients are presenting later in the course of their illness. In general, empiric antibiotic treatment should be considered for patients in endemic areas who present with an acute febrile illness suggestive of HGA.
For specific diagnosis, Wright or Giemsa-stained blood smears have a slightly higher yield than with HME, but are still not optimal for general clinical utility, given that there appears to be a wide variation (25-75%) in the sensitivity of these tests in visualizing morulae in host neutrophils. More helpful, but not always available, are polymerase chain reaction (PCR) tests, which are estimated to have a sensitivity of 67-90%. Prior antibiotic therapy dramatically reduces the sensitivity of both of these diagnostic methods.
Serologic testing is useful to confirm the diagnosis of anaplasmosis. The most commonly used method is indirect immunofluorescence (IFA) of IgM and IgG anti-A. phagocytophilum antibodies. Seroconversion is perhaps the most sensitive laboratory evidence of A. phagocytophilum infection, but is not always obtained in a timely enough manner to provide useful input on clinical (i.e., treatment) decisions.
The optimal dose and duration of antibiotic treatment for anaplasmosis has not been definitively established, but it is clear that A. phagocytophilum is highly sensitive to tetracyclines. Thus, oral doxycycline is the recommended treatment, at the same dose used for Ehrlichia infections: 200 mg/day in two divided doses. The usual treatment duration is 5-10 days, which is extended if there is suspected coinfection with B. burgdorferi, the agent of Lyme disease. In any case, treatment should continue for at least three days after the patient’s fever resolves. Response to treatment is usually rapid; if the patient remains febrile more than two or three days after initiation of doxycycline therapy, the diagnosis should be revisited.
As with Ehrlichia infections, rifampin is used in cases where doxycycline is contraindicated, such as pregnancy or allergy. Rifampin has also been used successfully in pediatric cases, and thus is sometimes employed in mild cases of pediatric A. phagocytophilum infection. If coinfection with B. burgdorferi is suspected in a pediatric case, doxycycline is sometimes used as an initial treatment for 3-5 days, with another antibiotic employed thereafter to complete the somewhat longer recommended treatment period for early Lyme disease.
Tularemia is a serious infection caused by the small, rod-shaped, nonmotile bacterium Francisella tularensis. The microbe has been found in over 100 species of mammals, birds, amphibians, arthropods, and even fish, and the disease occurs throughout North American and Eurasia. In the United States, it is most prevalent in the western and south-central parts of the country, but cases have been reported in every state but Hawaii.
The main animal hosts of F. tularensis are small mammals such as mice, voles, squirrels, rabbits and hares. They acquire the organism through the bite of an infected arthropod or by contact with contaminants in the environment. (F. tularensis can survive for weeks outside of a living host.) In humans, infection is usually caused by bites from Dermacentor or Amblyomma ticks in summer and from contact with rabbit carcasses in winter, but other modes of transmission occur, including contact with contaminated water, air or soil.
There are several different types of tularemia, which vary in presentation and severity depending on the method of acquisition and the dose and virulence of the specific infecting organisms. Typically, tularemia is divided into six forms: ulceroglandular, oculoglandular, glandular, oropharyngeal, typhoidal and pneumonic.
Ulceroglandular is the most common form by far, comprising around three-fourths of all cases of tularemia. In ulceroglandular tularemia, the organism is acquired through the skin via arthropod bite or abrasion. Usually, the vector is a tick, but deer flies and mosquitoes can also transmit F. tularensis. A skin ulcer develops at the site of infection.
Typhoidal tularemia (sometimes called septicemic tularemia) is the next most common type, at around 10-15% of cases, and is the most serious form. Pneumonia is a common feature. It is probably acquired by ingestion, although the precise mode of transmission is not completely clear.
Pneumonic tularemia is uncommon, and is acquired by inhalation. Some patients with ulceroglandular and, more often, typhoidal tularemia will also develop pneumonia.
Oculoglandular tularemia is rare and occurs when F. tularensis is introduced into the eye. This can occur from a splash of infected blood or perhaps when the eyes are rubbed after handling an infected animal carcass.
Oropharyngeal tularemia is also rare and is caused by ingesting undercooked meat from an infected animal (almost always a rabbit).
Glandular tularemia is also rare, and is clinically similar to the ulceroglandular form, except without the development of a skin ulcer. It is acquired through the skin, and may not require a scratch or abrasion.
Because F. tularensis can exist in aerosolized form and only 10 - 50 organisms are required to establish infection and cause disease, there is considerable concern that tularemia could be used as a bioweapon.
Signs and Symptoms
Symptoms of tularemia usually develop within three or four days of inoculation, though in some cases it can take up to 10 days for the disease to manifest. The organism is intracellular and spreads via the lymphatic system, multiplying within macrophages. Signs and symptoms, and the organs affected, vary widely depending on the method of inoculation.
In ulceroglandular and glandular tularemia, common early signs are high fever, chills, swollen glands, headache and extreme fatigue. A skin ulcer develops at the infection site in the ulceroglandular form.
Typhoidal tularemia is characterized by fever, exhaustion and weight loss. The lungs may become involved.
Sore throat, nausea, vomiting and diarrhea are common in the oropharyngeal form of tularemia. Abdominal pain and intestinal ulcerations are common.
Oculoglandular tularemia is marked by redness and pain in the eyes (conjunctivitis), often accompanied by a discharge. Swollen glands are also frequently seen.
Finally, pneumonic tularemia causes a dry cough, respiratory difficulty and chest pain.
Meningitis is an uncommon but potentially serious complication of tularemia.
Diagnosis of tularemia is based on the signs and symptoms described above, ideally combined with a history of recent arthropod bite or plausible environmental exposure to F. tularensis. The index of suspicion increases strongly with the presence of the characteristic ulcer.
Standard blood tests are not particularly helpful in diagnosing tularemia, although about half of all patients will exhibit non-specific abnormalities in liver function. Some patients develop elevated creatine kinase levels as a result of rhabdomyolosis; this is frequently associated with a poor prognosis.
A number of specific tests exist for tularemia, but they are not widely available. Direct examination of biopsy specimens or secretions by fluorescent antibody or Gram or histochemical stains is often helpful in diagnosis. F. tularensis can also be demonstrated microscopically with fluorescent-labeled antibodies. Antibodies are not typically present, however in the first ten days to so after exposure.
Polymerase chain reaction (PCR) tests can also be utilized.
F. tularensis can be grown in culture, although laboratory personnel are advised to take strong precautions before attempting to do so, as workers can themselves become infected. Ideally, patient samples should come from sputum or pharyngeal washings, as the organism is not present in large numbers in blood.
Parenteral antibiotic therapy with streptomycin is the treatment of choice for tularemia. Gentamicin is considered an acceptable alternative. The recommended treatment period is 10 days. In vitro susceptibility studies indicate that quinolones and fluoroquinolones are also effective against F. tularensis, thus providing an additional option for physicians.
Tetracyclines and chloramphenicol can also be used, but a higher rate of relapse is associated with these agents, as they are bacteriostatic rather than bactericidal. Thus, it is recommended that treatment with these medications be extended to 2-3 weeks.
If treatment is initiated in a timely fashion, the mortality rate for tularemia is low, around 1-2%. However, one-third of untreated patients will die, usually from pneumonia, meningitis or peritonitis.
Red Meat Allergy
Galactose-alpha-1, 3-galactose, or Alpha-Gal for short, is a delayed allergy to mammal meat affecting a growing number of the population. This allergy is initially caused by a tick bite. Since the reaction to eating mammal meat is delayed by several hours, the proper diagnosis is often missed or misdiagnosed. People who are afflicted with the Alpha-Gal allergy have to be constantly vigilant about the ingredients they consume, because an allergic reaction can be severe and life-threatening.
The bite of a particular tick, the Lone Star tick, can start a chain of reactions in some people. Lone Star ticks carry a sugar called alpha-gal, which is also found in red meat, but not in people. Normally, alpha-gal in meat poses no problems for people. But when a Lone Star tick bites a person, it transfers alpha-gal into the bloodstream. As a result, the person's body produces antibodies to fight the sugar. The next time that person eats meat from a mammal (including beef, pork, lamb, venison, goat and bison) the meat triggers the release of histamine, a compound found in the body that causes allergic symptoms like hives, itching and even anaphylaxis (a reaction that leads to sudden weakness, swelling of the throat, lips and tongue, difficult breathing and/or unconsciousness). Fish, turkey and chicken are not mammals, so they don’t have alpha-gal.
Most allergic reactions to foods occur almost immediately, but red meat allergic reactions can occur up to eight hours after a person eats meat. Often the reaction can be in the middle of the night and the connection to something they ate hours ago isn’t made easily.
The allergy most often occurs in the central and southern United States, which corresponds to the distribution of the lone star tick. In the Southern United States, where the tick is most prevalent, allergy rates are 32% higher than elsewhere. However, as doctors are not required to report the number of patients suffering the alpha-gal allergies, the true number of affected individuals is unknown.