ROCKY MOUNTAIN SPOTTED FEVER

Megan Alvarez, Keri Dobitz, & Donetta Hernandez

Vet Tech Institute of Houston

ETIOLOGY

Rickettsia rickettsii 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)

American Dog TickWood Tick

Lone Star TickBrown Dog Tick

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

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 non-purebred dogs and German shepherd dogs may be at higher risk than other breeds.

Humans

R. rickettsii has also been isolated from small mammals Opossums, rabbits, chipmunks, squirrels, rats, & mice

TRANSMISSION Transmitted by infected ticks through their

saliva when taking blood meals Generally, the tick must be attached to the host

for 5-20 hours for transmission of R. rickettsia to occur

Vector-borne Zoonotic Direct transmission from dogs to humans

have not been reported 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

Life cycle of Rickettsia rickettsii, the etiological agent of Rocky Mountain Spotted Fever.

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.

Fever Anorexia Depression Mucopurulent Ocular

Discharge Tachypnea Coughing Vomiting and Diarrhea Muscle Pain Acute Renal Failure Coma

Central Nervous Signs Ex: Ataxia

Severe Weight loss Retinal Hemorrhages Scrotal Edema Hypertension Shock Heart blocks or

arrhythmia Seizures Pulmonary Edema

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, 

RMSF Rash Rash appears 2-5 days after onset Macules– spots – wrists, forearms, ankles Spots can become raised

(non-itchy) 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

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

DIAGNOSTIC TESTS AND EXPECTED RESULTS CONT.

CBC Anemia Leukopenia to Leukocytosis Thrombocytopenia

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

Antibiotic treatment should be administered based on clinical suspicion, delayed treatment may result in a higher rate of severe or fatal outcome Doxycycline Tetracycline

Supportive care for dehydration Due to alterations in vascular integrity,

conservative rates of fluid administered are advised

FROM THE MERCK VET MANUAL

Doxycycline 5-10 mg/kg, PO or IV, SID for 10-21 days

Tetracycline 22 mg/kg, PO, TID for 2 weeks

MORBIDITY AND MORTALITY 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 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

PROGNOSIS

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

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

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.

Common acaricides currently available on the market include repellants such as 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.

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 TICK1. Use fine-tipped tweezers and protect your

fingers with a tissue, paper towel, or latex gloves. Avoid removing ticks with your bare hands.

2. 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.

3. 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

What is it? 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.

How can my dog get RMSF? 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? 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.

Is it treatable? 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? 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.

How can I protect my dog and myself from RMSF? 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

Summers, A. (2007). Common Diseases of Companion Animals. St. Louis: Mosby Elsevier.

http://www.cfsph.iastate.edu/DiseaseInfo/disease.php?name=rocky-mountain-spotted-fever&lang=en

http://www.cdc.gov/ticks/removing_a_tick.html http://www.peteducation.com/article.cfm?c=2+1556&aid=472 http://www.petside.com/health/petvet/rocky-mountain-spotted-fever-

canine.php http://www.petside.com/health/petvet/rocky-mountain-spotted-fever-

canine.php http://www.vetstream.com/canis/Content/Disease/dis60191 http://www.ivis.org/advances/Disease_Factsheets/RMSF.pdf http://www.peteducation.com/article.cfm?c=2+1556&aid=472 http://www.merckvetmanual.com/mvm/index.jsp?cfile=htm/bc/

57304.htm&word=rokcy%2cmountain%2cspotted%2cfever http://www.ivis.org/advances/Disease_Factsheets/RMSF.pdf http://www.drsfostersmith.com/pic/article.cfm?aid=62

http://textbookofbacteriology.net/themicrobialworld/Rickettsia.html

http://www.petside.com/health/petvet/rocky-mountain-spotted-fever-canine.php

http://www.peteducation.com/article.cfm?c=2+1556&aid=472

http://www.cdc.gov/ncidod/dbmd/diseaseinfo/ Common Diseases of Companion Animals

(Second Edition) by Alleice Summers