Download Rocky Mountain Spotted Fever - Dr. Brahmbhatt`s Class Handouts

ROCKY MOUNTAIN SPOTTED
FEVER
Megan Alvarez, Keri Dobitz, & Donetta Hernandez
Vet Tech Institute of Houston
ETIOLOGY
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Rickettsia rickettsii
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Small, gram negative, obligate intracellular
bacterial parasite from family Rickettsiacae
Tick-borne pathogen
Dermacentor variabilis (American Dog Tick)
 Dermacentor andersoni (Wood Tick)
 Amblyomma americanum (Lone Star Tick)
 Rhipicephalus sanguineus (Brown Dog Tick)
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American Dog Tick
Lone Star Tick
Wood Tick
Brown Dog Tick
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First recognized in 1896 in the Snake River Valley of Idaho
Originally called "black measles" because of the
characteristic rash.
Early 1900s, the geographic distribution of the disease was
recognized as far north as Washington and Montana and as
far south as California, Arizona and New Mexico.
Howard Ricketts was the first to establish the identity of
the infectious organism that causes Rocky Mountain
spotted fever at the turn of the Twentieth Century. He and
others characterized the basic epidemiologic features of the
disease, including the role of tick vectors.
The name Rocky Mountain spotted fever is somewhat of a
misnomer - Between 1981 and 1996, this disease was
reported from every U.S. state except Hawaii, Vermont,
Maine and Alaska.
Rocky Mountain Spotted Fever was not recognized in dogs
until the 1970
SIGNALMENT
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Rocky Mountain spotted fever occurs most often in
the spring and summer when ticks are most active.
Dogs at increased risk include those younger than
four years of age and large breed dogs primarily
because these dogs are more likely to be outdoors.
Purebred dogs are more likely to develop the
symptoms of RMSF after infection than are nonpurebred dogs and German shepherd dogs may be at
higher risk than other breeds.
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Humans
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R. rickettsii has also been isolated from small
mammals
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Opossums, rabbits, chipmunks, squirrels, rats, & mice
TRANSMISSION
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Transmitted by infected ticks through their
saliva when taking blood meals
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Generally, the tick must be attached to the host for 520 hours for transmission of R. rickettsia to occur
Vector-borne Zoonotic
 Direct transmission from dogs to humans have
not been reported
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Dogs can carry ticks that can infect humans or other
dogs
Infection can also result from contact with
Tick feces
 Tissues or fluids from tick removal
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Life cycle of Rickettsia rickettsii, the etiological agent of Rocky
Mountain Spotted Fever.
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Hard-bodied ticks such as the American dog tick
(Dermacentor variabilis) in the eastern Untied States and
the wood tick (Dermacentor andersoni) in the western
United States are carriers of the R. rickettsii organism.
Ticks acquire this organism when they feed on the blood of
small mammals such as foxes and raccoons.
Ticks usually have to be attached to the host animal for
five to twenty five hours to transmit the disease. The tick's
saliva transmits the disease during feeding. The disease is
transmitted faster later in the season than earlier in the
season, when the R. rickettsii organisms are slower to
activate. In the subclinical stage of the infection, dogs do
not show any outward symptoms. Dogs treated in the
subclinical stage have a better chance of a quick recovery.
When symptoms manifest, it is called the acute stage.
Human transmission of the disease occurs when
bitten by a tick that is carrying the bacterium R.
rickettsia.
 Because ticks on dogs can be infected with R.
rickettsii, dogs and people can get RMSF from the
same ticks.
 These ticks can also bite other animals and pass
RMSF to them.
 Dogs that are allowed to roam free can become
“tick buses” that spread infected ticks all over the
community.
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Fever
Anorexia
Depression
Mucopurulent Ocular
Discharge
Tachypnea
Coughing
Vomiting and Diarrhea
Muscle Pain
Acute Renal Failure
Coma
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Central Nervous Signs
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Ex: Ataxia
Severe Weight loss
Retinal Hemorrhages
Scrotal Edema
Hypertension
Shock
Heart blocks or
arrhythmia
Seizures
Pulmonary Edema
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Patients infected with R. rickettsii usually start having fevers and feeling
nauseous following an incubation period of about 5-10 days after a tick bite
The early clinical presentation of RMSF is often nonspecific and may
resemble many other infectious and non-infectious diseases. A few days
after the fever begins, initial symptoms may include nausea, vomiting,
muscle pain, lack of appetite and severe headache. Later signs and
symptoms include rash (especially on arms and/or ankles), abdominal pain,
joint pain, and diarrhea.
Three most common signs of RMSF are fever, rash, and a previous tick
bite,
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RMSF Rash
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Rash appears 2-5 days after onset
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Macules– spots – wrists, forearms, ankles Spots can become raised (nonitchy)
Rash spreads to trunk, etc.
Petechial rash (60%)–may not appear until 6 days after onset, or not at all
(10+%)
Rash usually involves palms and soles
DIAGNOSTIC TESTS AND EXPECTED
RESULTS
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Direct Imunofluorescent test of tissue biopsy
Indirect immunofluorescent test showing a fourfold
increase in serum titers
CBC: anemia,
leukopenia to leukocytosis,
thrombocytopenia
Serum Chemistry
Hypoproteinemia
 Hypocalcemia
 Increased liver enzyme
activity
 Hyponatremia
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DIAGNOSTIC TESTS AND EXPECTED
RESULTS
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CBC
Anemia
 Leukopenia to Leukocytosis
 Thrombocytopenia
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CONT.
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Several blood tests are available which test for the dog's
antibodies (proteins produced to fight off the infection) to R.
rickettsii. Since we need to look for a change in the antibody
levels, usually two tests will be done 2 weeks apart and the
results compared. Dogs with an active infection will show a
significant rise in the amount of antibody present.
A test is also available which detects antigens (protein parts)
of R. rickettsii. This test can become positive as early as 4 days
after the tick bite. This test is not a blood test, but a small
biopsy of the skin at the site of the tick bite is tested.
Dogs with Rocky Mountain Spotted Fever will have a low
white blood cell count early in the course of infection, and then
the cell numbers may increase. During the most severe phase
of the disease, the white blood cell counts may again drop,
along with the red blood cell counts and platelet numbers.
Other organs may be damaged, so liver enzymes, and kidney
function tests may be at abnormal levels.
TREATMENT
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Antibiotic treatment should be administered
based on clinical suspicion, delayed treatment
may result in a higher rate of severe or fatal
outcome
Doxycycline
 Tetracycline
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Supportive care for dehydration
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Due to alterations in vascular integrity, conservative
rates of fluid administered are advised
FROM THE MERCK VET MANUAL
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Doxycycline
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5-10 mg/kg, PO or IV, SID for 10-21 days
Tetracycline
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22 mg/kg, PO, TID for 2 weeks
MORBIDITY AND MORTALITY
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RMSF is usually seen from spring time to early
fall
Up to 63% of dogs in some areas will test positive
for the antibodies of RMSF
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this may be partially due to exposure to related
rickettsiae of the spotted fever group
The disease may be present as subclinical, mild,
or severe
German Shepherds may have a greater
predisposition to the more severe form of the disease
 English Springer Spaniels with phosphofructokinase
deficiency also may have more severe symptoms
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PROGNOSIS
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The subclinical form of RMSF may resolve on its own
without treatment
Improved health may be seen within 24-48 hrs after
starting antibiotic therapy in mild cases
If the disease reaches the severe stage, and the dog
has neurological signs or serious organ dysfunction,
death may occur
Patients who suffer damage to the nervous system
may never completely recover
Following recovery, the dog has good immunity
against ever becoming re-infected
German Shepherds and certain lines of English
Springer Spaniels tend to have a more severe form of
the disease and may not recover.
PATHOLOGIC LESIONS OF DISEASE
The Rickettsiae cause cytopathic changes which
result in damage to the endothelial layer of blood
vessels and internal organs
 Post-mortem indications of this process may be
necrotizing vasculitis, or petechiae and
eccymoses of the heart, brain, and lymph nodes
 Because of the damage to the blood vessels, the
blood supply to all body tissues and organs is
compromised and may result in thrombi, edema
in the face and extremities, or pulmonary edema
 In extreme case, necrosis of the extremities (acryl
gangrene) may occur
 Vasculitis and perivascular inflammatory cell
infiltrates may be seen in most of the body
tissues
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Perivascular inflammatory cell infiltrate comprised
predominantly of lymphocytes and macrophages; involved
vessels exhibit prominent swelling of endothelial cells
The rickettsia stain as red particles in the cytoplasm of
cells
R. rickettsii (red staining) infecting the endothelial cells of a blood
vessel
The appearance of intra-retinal hemorrhaging (dark gray,
round spots) is the most common ocular manifestation of
RMSF (mild clinical signs)
Necrotic area on right front extremity
PREVENTION
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Tick control is the most effective way to prevent
RMSF
Ticks prefer locations on the head and neck,
inside the ears, around the anus, near the
shoulder blades, or between the toes, but can be
found anywhere on your pet so check carefully
and remove the ticks immediately
PREVENTION CONT.
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Common acaricides currently available on the
market include repellants such as
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K9 Advantix (Imidacloprid Permethrin)
Bio-Spot Flea and Tick Spray for Dogs (Pyrethrin
Methoprene)
Frontline Plus (Fipronil Methoprene)
Preventic Tick Collar (Amitraz)
Promeris for Dogs (Metaflumizone Amitraz)
Revolution for Dogs (Selamectin)
Vectra 3D (Permthrin Dinotefuran)
PREVENTION CONT.
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It is important to spray the yard, patio, and dirt
areas with a yard spray. It may be necessary to
repeat this every week throughout the warm
weather with a product like Bio-Spot Yard and
Garden Spray. Be careful to keep your dogs
away from the treated area until the sprayed
areas are dry
No vaccine is available
HOW TO REMOVE A TICK
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Use fine-tipped tweezers and protect your
fingers with a tissue, paper towel, or latex
gloves. Avoid removing ticks with your bare
hands.
Grasp the tick as close to the skin surface as
possible and pull upward with steady, even
pressure. Don’t twist or jerk the tick; this can
cause the mouth-parts to break off and remain
in the skin. If this happens, remove the mouth
easily with clean tweezers, leave it alone and let
the skin heal.
After removing the tick, thoroughly disinfect the
bite and your hands with rubbing alcohol, and
iodine scrub, or soap and water.
Correct way to remove a tick
Blood from RMSF patients may be infectious to persons handling
it. Avoid contact by wearing protective clothing. Avoid blood
from the tick as well.
CLIENT EDUCATION
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What is it?
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Rocky Mountain Spotted Fever (RMSF) is a bacterial
infection that is spread by ticks. (Rickettsia
rickettsii). Humans, dogs and small mammals such as
rabbits, squirrels, mice etc, can become infected. The
first cases of RMSF were diagnosed in the Rocky
Mtn. states. However, now the disease is most
prevalent on the Atlantic and Pacific coasts as well as
the south central United States.
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How can my dog get RMSF?
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It is spread by the bite of an infected tick (the vector).
A tick that bites a small mammal which is carrying
the RMSF bacteria (with no signs of illness) then
carries the bacteria to a dog or human when it feeds
again (bloodmeal).
What symptoms might I see if I suspect my dog
has RMSF?
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The mild form of the disease may include fever,
swollen glands, coughing, diarrhea, vomiting, joint
and muscle pain. More severe symptoms may
include reddened eyes, vision problems, bleeding
from the nose or blood in the urine or stool. If the
brain is involved, you may see behavior changes,
head tremors, or difficulty standing.
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Is it treatable?
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Yes, most infected dogs respond well to antibiotics
and start to improve within a couple of days. The
earlier that treatment is started, the better the
changes of recovery.
Can I get RMSF from my dog?
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No, you cannot get RMSF from your dog. However, if
an infected tick bites you directly, you can get RMSF.
Several hours of attachment are necessary for the
bacteria to be transmitted. If you develop fever,
nausea, and body aches after tick exposure, contact
your physician immediately.
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How can I protect my dog and myself from
RMSF?
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Use tick prevention medications on your dog year
around. Keep your pet out of wooded areas and check
them for ticks often. If you are entering a wooded
area, wear long-sleeves and long-pants and check
yourself for any ticks. If you find a tick, remove it
carefully with gloved hands and then wash your
hands afterwards.
http://www.youtube.com/watch?v=WQGLpTSpgSM&feature=related
REFERENCES
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Summers, A. (2007). Common Diseases of Companion Animals. St. Louis: Mosby
Elsevier.
http://www.cfsph.iastate.edu/DiseaseInfo/disease.php?name=rocky-mountainspotted-fever&lang=en
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http://www.cdc.gov/ticks/removing_a_tick.html
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http://www.peteducation.com/article.cfm?c=2+1556&aid=472
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http://www.petside.com/health/petvet/rocky-mountain-spotted-fever-canine.php
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http://www.petside.com/health/petvet/rocky-mountain-spotted-fever-canine.php
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http://www.vetstream.com/canis/Content/Disease/dis60191
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http://www.ivis.org/advances/Disease_Factsheets/RMSF.pdf
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http://www.peteducation.com/article.cfm?c=2+1556&aid=472

http://www.merckvetmanual.com/mvm/index.jsp?cfile=htm/bc/57304.htm&word=rokc
y%2cmountain%2cspotted%2cfever
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http://www.ivis.org/advances/Disease_Factsheets/RMSF.pdf
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http://www.drsfostersmith.com/pic/article.cfm?aid=62
http://textbookofbacteriology.net/themicrobialwor
ld/Rickettsia.html
 http://www.petside.com/health/petvet/rockymountain-spotted-fever-canine.php
 http://www.peteducation.com/article.cfm?c=2+155
6&aid=472
 http://www.cdc.gov/ncidod/dbmd/diseaseinfo/
 Common Diseases of Companion Animals
(Second Edition) by Alleice Summers
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