Rocky Mountain Spotted Fever

Definition

A potentially mortal disease affecting dogs and humans, caused by a parasite called Rickettsia rickettsii which is transmitted by ticks ("american dog tick" and "wood tick"). 

Physiopathology

Following a tick bite, the organism invades the body and is dispersed in the blood where it causes dammages to the vessels' cells. These contract, inflammation ensues, and coagulation is activated. The cells of the affected tissues die, the number of platelets decreases, and there is an accumulation of fluid in the lungs, brain, and skin. The severity dammages to the organs (especially the kidneys, brain, heart, and skin) depends on the degree of local dammages. In explosive cases, inflammation can spread throughout the whole body. 

Symptoms

The disease can be characterized as clinical or subclinical (no obvious symptoms present).

When an animal is symptomatic, this can be localized to the affected organs or can be generalized. 

The symptoms are vague: 

  • Depression
  • Anorexia
  • Muscle and joint pain 
  • Vomiting 
  • Fever 2 to 3 days after exposure 
  • Coughing and difficulty breathing
  • Skin lesions: petechiae (small red spots on the skin and the gums), ecchymosis (bruising), edema (water accumulation), vesicles (blisters).

Differential diagnosis

Other parasitic diseases:

  • Acute Ehrlichiosis
  • Babesiosis
  • Borreliosis
  • Leptospirosis
  • Immune-mediated disease
  • Distemper
  • Bacterial discospondylitis 
  • Pneumonia
  • Acute renal failure 
  • Pancreatitis 
  • Colitis 
  • Meningitis 

Diagnostic tests

General tests:

Blood tests

  • Light to severe anemia, decrease in platelet number, decrease or increase in white blood cells. 
  • Decrease in the amount of proteins and albumin, sodium, and calcium.
  • Increase in renal and hepatic enzymes.

Analysis of the cerebrospinal fluid (if there are neurological symptoms): Increase in proteins and white blood cells.

Specific tests:  

  • Antibody titer
  • Immunofluorescence to detect antigens in the tissues (biopsy or autopsy)
  • DNA tests 
  • Organism culture: not often done

Treatment

Antibiotics for a period of 2 to 3 weeks 

Corticosteroids: can lessen the complications associated with hyperactivity of the neurological system. 

Intravenous fluids and other supportive treatments to improve organ perfusion. 

Prevention

Tick protection                                                                                       Once healed, immunity is acquired for life. 

Prognosis

Excellent when quickly diagnosed.

Mortality is more likely when the diagnosis is delayed, the disease is very severe, or when using ineffective antibiotics.

Public health

There is no direct transmission from dogs to humans, but the presence of infected dogs in a human environment increases their risk of infection. 

Endemic regions

The disease is found in North America, South America, and Central America. Most of the cases in the United States occur in the Southeastern states. 

Comments/other species

The disease is found in North America, South America, and Central America. Most of the cases in the United States occur in the Southeastern states.