EhrlichiosisIntroduction: This
rickettsia-like infection is caused by small bacteria that can only multiply inside
two special white blood cell types, called monocytes and granulocytes. In the cycle of infection brown dog
ticks are involved as carriers, although it is not yet fully known
where the main reservoir for Ehrlichia species is. Two types are well described
in the medical literature: Ehrlichia chaffeensis , which multiplies specifically
in monocytes in the human host and causes human monocytic ehrlichiosis (HME).
The other type is Ehrlichia phagocytophilia, which multiplies in granulocytes
(=pus cells) and is the cause of human granulocytic ehrlichiosis(HGE). These two
types are found in the US with HME being more common in southern states, whereas
HGE has been found more in the upper midwestern and northeastern states. There
is another variety of ehrlichiosis, which is found in Japan and is called Sennetsu
fever. Signs and symptoms: The American ehrlichiosis
is a non specific flu-like illness, which starts 1 to 3 weeks after a tick bite
with fever, lack of appetite, muscle aches, headaches, nausea and vomiting. Occasionally
the onset is more abrupt and symptoms more acute. In the more acute form a life
threatening condition, called disseminated intravascular coagulation (DIC), is
developing.
This leads to lack of clotting, a loss of platelets
and possible shock and death, if not recognized early and treated successfully.
Liver function can also be affected and deteriorates, if the disease is more severe.
Diagnostic
tests: The clinical history of tick bites followed by the signs
and symptoms mentioned above, suggests the diagnosis clinically. Blood
tests are then done to confirm or rule out the disease. Low platelet counts (thrombocytopenia),
low white blood count (leukopenia) and elevated liver enzymes( transaminases)
in this setting point to this diagnosis. The specific tests are either a serological
test specific for ehrlichiosis showing the bacterium in the monocyte
(see arrow) or a genetic test involving a polymerase chain reaction,
which allows earlier diagnosis of this disease before DIC sets in. Treatment: Treatment is given based on
the clinical presumptive diagnosis, as early treatment will quickly eradicate
the disease and prevent complications such as DIC, shock and death. Tetracycline
or doxycycline is the treatment of choice except for pregnant women, where chloramphenicol
is the accepted alternative. There is a small risk of agranulocytosis from chloramphenicol,
but most physicians agree that the risk of not treating the ehrlichiosis is greater
than the risk of agranulocytosis. Further information
from the CDC. |
