What causes Rocky Mountain Spotted Fever (RMSF)?
Rickettsia ricketsii, a gram negative, obligately intracellular bacteria
What type of illness is RMSF?
An acute, febrile illness
What is the vector (non-specific) for Rickettsia ricketsii?
Where does RMSF commonly occur in US?
In southeastern and south central states - where the ticks are present
What cells does R. ricketsii infect?
endothelial cells by inducing phagocytosis by these cells
Once R. rickettsii infects endothelial cells, what does it do?
It causes damage to the endothelial cells leading to vasculitis and increased microvascular permeability. This permeability leads to tissue edema
Is RMSF an acute or chronic disease?
What will you find on PE in patients with RMSF?
Fever (80% of naturally infected dogs), ocular signs, splenomegaly, lymphadenomegaly, nasal discharge, tachypnea, epistaxis, petechia, ecchymoses, peripheral edema, gangrenous necrosis, orchitis and scrotal edema, CNS signs, and generalized pain This is a lot of signs, but she specifically highlighted fever
What will you find on CBC in patients with RMSF?
Thrombocytopenia, leukocytosis, and mild non-regenerative anemia
What will you find on chemistry in patients with RMSF? UA?
Chemistry - Hypoalbuminemia (from vasculitis) UA - variable (proteinuria, hematuria, and bilirubinuria)
True or False: RMSF suspected patients should be treated before diagnostic test results are returned.
True - the tests take too long
How is RMSF diagnosed?
Serology (IFA) and PCR
How is RMSF treated?
Doxycycline and supportive care
What is the prognosis for RMSF?
Good to excellent if diagnosed and treated early
How is RMSF prevented?
with tick prevention
Can humans get RMSF from their dogs?
Not exactly, they can be sentinels of tick exposure. They personally cannot give it to humans, but the ticks on the dogs can.
Pete is a 7 YO MC Golden that has presented for a 3 day history of lethargy, inappetence, and vomiting. This is the first time in his life that he has not eaten. You practice in NC. He is on flea and HW prevention, not tick prevention. On his PE you note he has a 103.7 F fever, he is 5-7% dehydrated, there is ocular mucoid discharge in both eyes, and the fundic exam is WNL. There are prominent submandibular and prescapular LNs and a slightly stiff gait. His CBC reveals thrombocytopenia, and slight neutrophilia. The chemistry panel reveals albumin and the UA reveals a USG of 1.026 and 1+ protein.
What do you want to do next for pete?
a. He must have Babesia because he lives in the South. Start imidocarb right away.
b. Systemic workup including abdominal x-rays and ultrasound. Just because this is an infectious disease lecture doesn't mean he has an infectious disease.
c. Culture his urine because he has a fever and proteinuria.
d. Perform a 4Dx SNAP test.
B, C, and D
Which of the following doxycycline responsive infections is associated with a vasculitis that can lead to peripheral edema because the causative organism infects endothelial cells?
a. Mycoplasma haemofelis
b. Rickettsia rickettsii
c. Ehrlichia canis
d. Anaplasma phagocytophilum
e. Babesia canis vogeli
b. Rickettsia rickettsii
What causes Lyme Borreliosis?
Borrelia burgdorferi a motile corkscrew-shaped (spirochete) bacteria
What clinical signs are associated with lyme disease?
Most dogs have no signs of illness but they can have fever, arthritis, and renal disease
In endemic areas, what percentage of dogs have been exposed to Lyme?
up to 80%
What tick genus is responsible for transmitting Borellia burgdorferi?
Ixodes (specifically the ricinus-persulcatus complex) - this also transmits A. phagocytophilum
What animals are reservoirs for Borellia burgdorferi?
Peromyscus leucopus (white-footed mouse) in the NE and upper Midwest
How does B. burgdorferi adhere to the tick midgut?
Lipoprotein OspA expression
How does B. burgdorferi bind disseminate in the mammalian host?
Lipoprotein OspC expression which is upregulated when a tick ingests mammalian blood
What percentage of dogs will show overt illness signs of Lyme disease?
What are the clinical features of Lyme disease?
Fever, lameness (joint closest to tick bite is first affeced), mild to moderate thrombocytopenia, and Lyme associated nephritis
What is Lyme-associated nephritis?
In patients that develop Lyme-associated nephritis, what is the prognosis?
What will the chemistry and UA show in patients with Lyme-associated nephritis?
Chemistry - Hypoalbuminemia +/- azotemia UA - isosthenuria and proteinuria