Babesiosis: Increasing Incidence -- Stay Alert
Babesiosis: Increasing Incidence -- Stay Alert
Hello. This is Paul Auwaerter with Medscape Infectious Diseases, speaking from the Division of Infectious Diseases at Johns Hopkins University School of Medicine. The spring and summertime months often bring the concern of tickborne infections. Recently, 18 state health departments and the Washington, DC, health department have worked with the Centers for Disease Control and Prevention to develop a common case report form for one of the less common tickborne infections -- the parasite Babesia.
This new case report form has led to more rigorous surveillance for this infection, and in the recent Morbidity and Mortality Weekly Report,results from surveillance for the year 2011 were released. I found this interesting. Babesia is an intracellular parasite that attacks red blood cells and is transmitted by Ixodes scapularis (Figure), the same deer tick as that which transmits Lyme disease or human granulocytic anaplasmosis. Problems can vary from being completely asymptomatic to a severe and devastating illness, often in elderly or immunocompromised patients.
In this report, 1124 patients were described as having probable or definitive evidence of Babesia infection. This report includes only 18 states, but the range covers most of the Lyme disease territories. This number is about 1/20th of the usual number of reported Lyme disease cases (often 20,000-30,000 per year).
Most of these cases came from just 7 states, and they are the ones you might suspect on the basis of typical coastal islands that have a high prevalence, such as Nantucket or Martha's Vineyard. The leading states are New York, Connecticut, Massachusetts, Rhode Island, New Jersey, Wisconsin, and Minnesota. More cases have been reported in recent years in New York, especially on Long Island and even in the Westchester region, but this parasite has not reached as southerly as Lyme disease has. Cases are reported in New Jersey, but none in Delaware, and there was only a single case in Maryland in 2010. So, this is something that may have a bit of a creeping range and will need attention.
More than one half (57%) of patients were older than 60 years of age, so at least for those that fit into the case reports, it looked as though older age is definitely a risk factor for symptomatic infection. All of the organisms were Babesia microti, as opposed to some of the other, more rare forms of Babesia, such as Babesia duncani or divergens-like organisms that have been described in several other states. Ten cases were the result of transfusion, and Babesia remains 1 of the most common causes of transfusion-related infection in the United States.
There was a lovely article by Vannier and Krause in the New England Journal of Medicine reviewing Babesia. A key point from that article was the need to maintain a high index of suspicion, because the organism often causes nonspecific symptoms, such as fever, muscle aches, and anemia -- although it is more of a hemolytic anemia, often accompanied by thrombocytopenia or liver function test abnormalities. This can be the same kind of picture that might be seen with Ehrlichia or anaplasma infection.
Traditionally, the blood smear has been the classic way to make this diagnosis, as you would with malaria. The best tests today are probably polymerase chain reaction (PCR) or nucleic acid amplification tests that can give you a more sensitive assay, although not as quickly, depending on processing times and location of testing.
It is uncommon to make a diagnosis by serology these days, and in fact, lower titers are often not meaningful. Titers of 1:512 or 1:1024 are needed to be supportive of acute infection.
Typically, 7-10 days of antimicrobials are required to help clear this infection, although occasionally, especially in immunocompromised patients, this can be more difficult. Higher-dose azithromycin (600-1000 mg daily), combined with atovaquone, has been used to help treat patients who have Babesia infection that is refractory to initial treatment.
Exchange transfusion, as for malaria, can be helpful for patients with severe infection and high parasitemic loads. This is especially true in Europe, where more virulent disease from B divergens as opposed to B microti might be seen.
Babesia is probably increasing relative to our common beliefs about the incidence of Babesia infection. Certainly, you should suspect it, especially if someone in whom you suspect a tickborne illness doesn't respond quickly to doxycycline therapy. Transfusion is also capable of transmitting the infection. At least in the 2011 surveillance data, only 0.8% of patients with Babesia infection had a coinfection with either Lyme disease or Anaplasma, so this should be kept in mind, although it is usually more troublesome the other way around in terms of anticipating a coinfection.
Hello. This is Paul Auwaerter with Medscape Infectious Diseases, speaking from the Division of Infectious Diseases at Johns Hopkins University School of Medicine. The spring and summertime months often bring the concern of tickborne infections. Recently, 18 state health departments and the Washington, DC, health department have worked with the Centers for Disease Control and Prevention to develop a common case report form for one of the less common tickborne infections -- the parasite Babesia.
This new case report form has led to more rigorous surveillance for this infection, and in the recent Morbidity and Mortality Weekly Report,results from surveillance for the year 2011 were released. I found this interesting. Babesia is an intracellular parasite that attacks red blood cells and is transmitted by Ixodes scapularis (Figure), the same deer tick as that which transmits Lyme disease or human granulocytic anaplasmosis. Problems can vary from being completely asymptomatic to a severe and devastating illness, often in elderly or immunocompromised patients.
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Figure. Ixodes scapularis (deer tick). |
In this report, 1124 patients were described as having probable or definitive evidence of Babesia infection. This report includes only 18 states, but the range covers most of the Lyme disease territories. This number is about 1/20th of the usual number of reported Lyme disease cases (often 20,000-30,000 per year).
Most of these cases came from just 7 states, and they are the ones you might suspect on the basis of typical coastal islands that have a high prevalence, such as Nantucket or Martha's Vineyard. The leading states are New York, Connecticut, Massachusetts, Rhode Island, New Jersey, Wisconsin, and Minnesota. More cases have been reported in recent years in New York, especially on Long Island and even in the Westchester region, but this parasite has not reached as southerly as Lyme disease has. Cases are reported in New Jersey, but none in Delaware, and there was only a single case in Maryland in 2010. So, this is something that may have a bit of a creeping range and will need attention.
More than one half (57%) of patients were older than 60 years of age, so at least for those that fit into the case reports, it looked as though older age is definitely a risk factor for symptomatic infection. All of the organisms were Babesia microti, as opposed to some of the other, more rare forms of Babesia, such as Babesia duncani or divergens-like organisms that have been described in several other states. Ten cases were the result of transfusion, and Babesia remains 1 of the most common causes of transfusion-related infection in the United States.
There was a lovely article by Vannier and Krause in the New England Journal of Medicine reviewing Babesia. A key point from that article was the need to maintain a high index of suspicion, because the organism often causes nonspecific symptoms, such as fever, muscle aches, and anemia -- although it is more of a hemolytic anemia, often accompanied by thrombocytopenia or liver function test abnormalities. This can be the same kind of picture that might be seen with Ehrlichia or anaplasma infection.
Traditionally, the blood smear has been the classic way to make this diagnosis, as you would with malaria. The best tests today are probably polymerase chain reaction (PCR) or nucleic acid amplification tests that can give you a more sensitive assay, although not as quickly, depending on processing times and location of testing.
It is uncommon to make a diagnosis by serology these days, and in fact, lower titers are often not meaningful. Titers of 1:512 or 1:1024 are needed to be supportive of acute infection.
Typically, 7-10 days of antimicrobials are required to help clear this infection, although occasionally, especially in immunocompromised patients, this can be more difficult. Higher-dose azithromycin (600-1000 mg daily), combined with atovaquone, has been used to help treat patients who have Babesia infection that is refractory to initial treatment.
Exchange transfusion, as for malaria, can be helpful for patients with severe infection and high parasitemic loads. This is especially true in Europe, where more virulent disease from B divergens as opposed to B microti might be seen.
Babesia is probably increasing relative to our common beliefs about the incidence of Babesia infection. Certainly, you should suspect it, especially if someone in whom you suspect a tickborne illness doesn't respond quickly to doxycycline therapy. Transfusion is also capable of transmitting the infection. At least in the 2011 surveillance data, only 0.8% of patients with Babesia infection had a coinfection with either Lyme disease or Anaplasma, so this should be kept in mind, although it is usually more troublesome the other way around in terms of anticipating a coinfection.
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