RMSF

Rocky Mountain Spotted Fever (RMSF) is a serious and potentially fatal tick-borne bacterial infection caused by Rickettsia rickettsii that affects dogs and humans throughout the Americas. Despite its name suggesting geographic limitation to mountain regions, RMSF occurs throughout much of the United States, with highest incidence in the southeastern and south-central states. This disease represents one of the most severe tick-borne infections affecting dogs, capable of causing rapid clinical deterioration and death within days if not promptly recognized and treated. The gravity of RMSF makes awareness of its presentation and the urgency of treatment essential for owners and veterinarians in endemic areas.

The pathophysiology of RMSF involves bacterial invasion and multiplication within the endothelial cells lining blood vessels throughout the body. Rickettsia rickettsii is an obligate intracellular bacterium, meaning it can only survive and reproduce inside host cells. After transmission through tick bite, the bacteria spread via the bloodstream and lymphatics to infect vascular endothelium in virtually every organ system. This widespread vascular infection produces vasculitis, or inflammation of blood vessels, which underlies all clinical manifestations of the disease. Damaged blood vessels become leaky, leading to edema, hemorrhage, and impaired blood supply to affected tissues and organs.

Clinical presentation of RMSF in dogs typically involves acute onset of severe illness developing two to fourteen days following infected tick attachment. High fever is nearly universal and often exceeds 104°F. Dogs appear profoundly ill with lethargy, depression, and complete loss of appetite. Characteristic features include peripheral edema affecting the limbs, face, and scrotum; petechial hemorrhages visible as tiny red spots on gums and skin; and neurological signs ranging from depression to seizures. The disease progresses rapidly, and dogs can deteriorate from apparently minor illness to life-threatening condition within days. Without treatment, mortality rates in dogs are significant, particularly among certain breeds.

Treatment of RMSF constitutes a medical emergency requiring immediate initiation of appropriate antibiotic therapy. Doxycycline is the treatment of choice and dramatically improves outcomes when started early. Dogs with suspected RMSF should begin treatment immediately based on clinical suspicion without waiting for confirmatory laboratory results, as delays worsen prognosis substantially. Supportive care addresses specific complications including fluid therapy, blood transfusions if needed, and management of organ dysfunction. With prompt, aggressive treatment, most dogs survive and recover fully. Prevention through consistent tick control remains the most effective strategy for avoiding this potentially devastating infection.

The causative agent of Rocky Mountain Spotted Fever is Rickettsia rickettsii, a small gram-negative obligate intracellular bacterium belonging to the spotted fever group of Rickettsia. This organism cannot survive outside host cells and has evolved sophisticated mechanisms for entering, surviving within, and exploiting eukaryotic cells. Rickettsia rickettsii is considered one of the most pathogenic members of the Rickettsia genus, capable of causing severe disease in both dogs and humans. The bacteria maintain their lifecycle between tick vectors and mammalian hosts, with dogs and humans serving as incidental dead-end hosts that develop disease but do not contribute significantly to ongoing transmission.

Tick vectors responsible for transmitting RMSF to dogs vary by geographic region. The American dog tick (Dermacentor variabilis) serves as the primary vector in the eastern United States and California. The Rocky Mountain wood tick (Dermacentor andersoni) transmits the disease in the Rocky Mountain states. The brown dog tick (Rhipicephalus sanguineus) has emerged as an important vector, particularly in the southwestern United States and areas with high brown dog tick populations. More recently, the Gulf Coast tick (Amblyomma maculatum) has been implicated in transmission. Ticks acquire infection by feeding on infected small mammals, then transmit bacteria to subsequent hosts during blood meals.

Environmental and geographic factors profoundly influence RMSF risk. Despite the disease name, cases occur throughout the contiguous United States, with highest incidence in North Carolina, Oklahoma, Arkansas, Tennessee, and Missouri. Any area with suitable tick habitat and infected tick populations can experience RMSF. Seasonal patterns show peak transmission during warmer months corresponding to increased tick activity, typically April through September in most regions. Year-round transmission occurs in southern areas with mild winters. Urban and periurban settings with abundant brown dog tick populations may have high transmission, and outbreak situations have been documented in specific communities.

Dog-related risk factors include tick exposure through outdoor lifestyle, lack of effective tick prevention, and living in or traveling to endemic areas. Working dogs, hunting dogs, and dogs with regular access to tick habitat face elevated exposure risk. Dogs without consistent tick preventative treatment have dramatically higher infection rates. Young adult dogs may be slightly overrepresented in case reports, possibly reflecting their activity levels and outdoor exposure. All breeds are susceptible, though German Shepherds and possibly other purebred dogs may develop more severe disease when infected. Previous RMSF infection does not confer complete protective immunity.

The mechanism of disease following tick-transmitted infection involves vascular endothelial cell targeting and subsequent vasculitis. After inoculation during tick feeding, Rickettsia rickettsii organisms spread through blood and lymph to reach small and medium blood vessels throughout the body. The bacteria specifically invade endothelial cells using specialized surface proteins that mediate attachment and entry. Once inside cells, bacteria escape the phagosome and multiply freely in the cytoplasm. Infected cell death releases bacteria to infect additional cells while triggering inflammatory responses. Vasculitis results in increased vascular permeability causing edema, microthrombi formation, and tissue hypoxia. Virtually every organ can be affected, with particularly serious consequences in brain, kidneys, and lungs.

Early warning signs of Rocky Mountain Spotted Fever may be subtle initially but typically progress rapidly to obvious illness. Within the first one to two days of clinical disease, dogs often show nonspecific signs including mild lethargy, decreased enthusiasm for food or activities, and slightly elevated body temperature that owners may not notice without measurement. Some dogs exhibit mild stiffness or reluctance to move. These early signs are easily attributed to minor illness or simply being tired. The critical point is that RMSF can progress from these vague early signs to life-threatening illness within just two to three days, making recognition of the trajectory rather than just individual signs important.

Common symptoms of RMSF develop as the disease progresses and vascular damage becomes widespread. High fever ranging from 104°F to 106°F is nearly universal and often the most obvious initial sign owners notice. Profound lethargy develops, with dogs becoming weak, reluctant to stand, and showing no interest in surroundings. Complete anorexia is typical. Joint and muscle pain causes stiffness, painful movement, and vocalization when handled. Many dogs develop a characteristic cough or respiratory difficulty as pulmonary involvement progresses. Vomiting and diarrhea may occur. The combination of high fever with rapidly progressive weakness should raise strong suspicion for RMSF in endemic areas during tick season.

Behavioral changes in dogs with RMSF reflect severe systemic illness affecting multiple organ systems. Depression progresses from mild lethargy to near unresponsiveness in severe cases. Dogs may become anxious or restless due to difficulty breathing or neurological effects. Some dogs vocalize apparently due to pain. Complete disinterest in food, water, and surroundings indicates severe illness. Dogs may seek isolation or conversely become unusually clingy. Confusion or disorientation suggests neurological involvement. Changes in gait ranging from stiffness to inability to walk may occur. House-trained dogs commonly have accidents due to weakness or altered mentation.

Physical signs of RMSF are distinctive and help differentiate this disease from other causes of acute febrile illness. Peripheral edema, or swelling of dependent areas, characteristically affects the limbs, ears, lips, prepuce or scrotum, and muzzle. This edema may be dramatic and is caused by increased vascular permeability. Petechial hemorrhages appear as tiny red to purple spots on the gums, inside ear flaps, whites of eyes, and unpigmented skin. Larger bruises (ecchymoses) may develop. Gums may appear pale if anemia develops or hyperemic (dark red) from vasculitis. Eye abnormalities including redness, discharge, and anterior chamber inflammation (uveitis) occur frequently. Lymph nodes may be enlarged. Scrotal swelling and necrosis can occur in intact male dogs.

Symptom progression in RMSF is notably rapid compared to many other infectious diseases. Dogs may appear relatively stable one day and be critically ill the next. Fever persists and may increase. Edema typically worsens over one to three days. Bleeding tendencies increase as thrombocytopenia progresses, with spontaneous hemorrhage occurring in severely affected dogs. Respiratory symptoms progress from mild cough to respiratory distress as pulmonary edema and hemorrhage develop. Neurological signs including depression, head tilt, seizures, or coma indicate central nervous system involvement, which carries poor prognosis. Kidney failure may develop, causing decreased urination and uremia. Without treatment, death can occur within one to two weeks of symptom onset.

Emergency symptoms requiring immediate veterinary care include signs suggesting severe or rapidly progressive disease. Respiratory distress manifested as labored breathing, open-mouth breathing, or blue-tinged gums constitutes immediate emergency. Neurological symptoms including seizures, collapse, inability to stand, or altered consciousness require urgent intervention. Profuse hemorrhage including bloody vomit, bloody diarrhea, or severe nosebleed indicates critical illness. Any dog with suspected RMSF showing rapid deterioration over hours needs emergency evaluation. In endemic areas during tick season, any dog with high fever, depression, and peripheral edema should be evaluated urgently for possible RMSF.

Initial veterinary examination for suspected RMSF involves urgent assessment given the potentially rapid disease progression. The physical examination evaluates fever, edema distribution and severity, evidence of petechiae or hemorrhage, respiratory status, and neurological function. Careful examination of gums, inner ear flaps, and unpigmented skin searches for characteristic petechial hemorrhages. Assessment of hydration status guides fluid therapy needs. History taking focuses on tick exposure, geographic location, timeline of symptom development, and any previous illnesses. In endemic areas during tick season, a dog presenting with fever, depression, and peripheral edema should be considered to have RMSF until proven otherwise.

Laboratory testing provides supporting diagnostic evidence though results may not be immediately available. Complete blood count commonly reveals thrombocytopenia (low platelets), which is present in most RMSF cases and may be severe. Anemia may develop as disease progresses. White blood cell counts are variable. Serum chemistry often shows elevated liver enzymes and low albumin reflecting hepatic involvement and vascular leak. Azotemia indicates kidney involvement and carries poor prognosis. Electrolyte abnormalities may occur. Coagulation testing assesses bleeding risk. Urinalysis may show proteinuria and, in severe cases, decreased urine specific gravity indicating kidney dysfunction. These findings support the diagnosis but are not specific to RMSF.

Definitive diagnosis of RMSF relies on specific testing for Rickettsia rickettsii infection. Serologic testing using indirect immunofluorescence assay (IFA) detects antibodies against the organism, but antibody development takes one to two weeks, making serology unhelpful for immediate diagnosis. Paired serum samples showing four-fold titer rise provide stronger evidence. PCR testing can detect rickettsial DNA in blood during acute infection, providing earlier diagnosis than serology, though false negatives occur. Immunohistochemistry on skin biopsy specimens can identify organisms in blood vessels. In practice, diagnosis is often made on clinical grounds with treatment initiated immediately, and laboratory confirmation obtained subsequently.

Differential diagnosis for RMSF includes other causes of acute febrile illness with vascular manifestations. Other rickettsial diseases including ehrlichiosis produce similar presentations but typically progress less rapidly. Immune-mediated thrombocytopenia causes petechiae and bleeding but usually without high fever and edema. Leptospirosis shares fever, kidney involvement, and bleeding but typically lacks the dramatic peripheral edema. Disseminated intravascular coagulation from any cause produces bleeding manifestations. Systemic vasculitis from autoimmune disease may appear similar. Heat stroke causes acute collapse and can produce coagulation abnormalities. Given the need for immediate treatment and the consequences of delay, treatment is initiated based on clinical suspicion without waiting for definitive diagnosis.

Emergency treatment for RMSF must begin immediately upon clinical suspicion, as treatment delays directly correlate with increased mortality. The single most important intervention is prompt initiation of doxycycline therapy. Doxycycline is the treatment of choice for RMSF in dogs and should be started without waiting for laboratory confirmation. Standard dosing is 5 mg/kg twice daily or 10 mg/kg once daily. Dogs unable to take oral medication receive intravenous doxycycline. Response to treatment is often evident within 24-48 hours in dogs without severe complications, with fever resolution being an early indicator of response. Delay of even one to two days in starting appropriate antibiotics significantly worsens prognosis.

Supportive care addresses the multiple organ effects of RMSF while antibiotics work to eliminate the infection. Intravenous fluid therapy corrects dehydration, supports circulation, and maintains renal perfusion. Fluid rates must be balanced against the risk of exacerbating pulmonary edema in dogs with significant vascular leak. Colloid solutions may help maintain intravascular volume. Blood or plasma transfusion is indicated for dogs with severe anemia or coagulopathy. Oxygen supplementation supports dogs with respiratory compromise. Temperature management addresses persistent high fever. Gastroprotection prevents gastrointestinal ulceration in stressed patients.

Management of specific complications requires targeted intervention. Dogs with severe thrombocytopenia and active bleeding may benefit from platelet-rich plasma if available, though platelet transfusions are not universally accessible. Neurological complications including seizures require anticonvulsant therapy and careful monitoring. Acute kidney injury demands appropriate fluid management and potentially dialysis in severe cases. Respiratory failure from pulmonary edema or hemorrhage may require mechanical ventilation. Dogs with severe disease often require intensive care unit hospitalization for continuous monitoring and support. The intensity of supportive care needed correlates with disease severity at presentation.

Alternative antibiotics are occasionally considered when doxycycline is contraindicated or unavailable. Chloramphenicol has historical use for RMSF but carries risk of bone marrow suppression and is generally less preferred. Tetracycline can be used but requires more frequent dosing than doxycycline. Fluoroquinolones have some activity but are considered inferior to doxycycline. In very young puppies where tetracycline tooth staining is a concern, the life-threatening nature of RMSF means treatment benefits far outweigh cosmetic concerns. No effective alternative approaches or complementary treatments exist for RMSF; antibiotic therapy is essential and should not be delayed for any reason.

Treatment duration for RMSF is typically 14-21 days of doxycycline therapy, though some sources recommend continuing until several days after fever resolution with a minimum 7-day course. Shorter courses risk relapse. Dogs showing clinical improvement should complete the full prescribed course. Treatment response is assessed through clinical improvement including fever resolution, improved appetite and energy, and resolution of edema. Laboratory improvement including platelet count normalization confirms response. Dogs failing to improve within 48-72 hours require reassessment of diagnosis and consideration of concurrent conditions or complications.

Treatment decisions in RMSF prioritize rapid intervention over perfect diagnosis. In endemic areas during tick season, dogs presenting with compatible clinical signs should receive immediate doxycycline therapy while diagnostic evaluation proceeds. The consequences of withholding treatment from a dog with RMSF far outweigh those of treating a dog who turns out to have a different diagnosis. Hospitalization is indicated for moderate to severe cases and any dog with complications. Cost considerations should not delay treatment initiation, though the expense of prolonged intensive care should be discussed honestly with owners of critically ill dogs.

Recovery timeline for RMSF varies dramatically based on disease severity at treatment initiation. Dogs treated early in the disease course, before severe organ damage occurs, often show rapid improvement within 24-48 hours of starting doxycycline. Fever typically resolves first, followed by improved appetite and energy over subsequent days. Peripheral edema resolves over several days to a week. Dogs with uncomplicated RMSF treated promptly often return to normal function within one to two weeks of treatment initiation. However, dogs with severe complications or delayed treatment face prolonged recovery periods extending weeks to months, and some develop permanent sequelae.

Post-treatment care focuses on completing the antibiotic course and monitoring for adequate response. Doxycycline must be continued for the full prescribed duration even after clinical improvement to ensure infection elimination. Activity should be gradually increased as strength returns, avoiding strenuous exercise until fully recovered. Follow-up laboratory testing confirms resolution of thrombocytopenia and other abnormalities. Dogs with kidney or liver involvement need monitoring of organ function during recovery. Nutritional support maintains strength during recovery. Tick prevention should be implemented immediately if not already in place to prevent reinfection.

Prognostic factors for RMSF outcomes include time from symptom onset to treatment initiation, disease severity at presentation, specific organ involvement, and individual dog factors. Dogs treated within the first one to two days of symptoms have excellent prognosis, with greater than 90% survival reported in some studies. Delayed treatment dramatically worsens outcomes, with mortality increasing significantly when treatment is delayed beyond the first few days. Neurological involvement carries poor prognosis and may result in permanent deficits even with successful treatment. Acute kidney injury requiring dialysis has guarded prognosis. German Shepherds may have higher mortality rates than other breeds. Young puppies and senior dogs may have poorer outcomes.

Long-term outlook for dogs surviving RMSF is generally good once recovery is achieved. Most dogs return to completely normal function without lasting effects. Neurological deficits from central nervous system involvement may be permanent in some dogs. Chronic kidney disease may result from severe acute kidney injury. Dogs recovered from RMSF remain susceptible to reinfection and do not develop reliable immunity. Lifelong tick prevention is strongly recommended for all dogs in endemic areas, particularly those with previous RMSF. Annual tick-borne disease screening can be considered for high-risk dogs. Understanding that RMSF can recur reinforces the importance of consistent prevention.

Primary prevention of Rocky Mountain Spotted Fever centers on preventing tick attachment and transmission. Year-round tick prevention using veterinarian-recommended products provides the foundation of prevention. Available products include topical applications (spot-ons), oral medications (both monthly and longer-duration options), and tick collars. Products should be effective against the tick species in the dog's geographic area, including Dermacentor ticks and Rhipicephalus sanguineus. Consistent application following manufacturer guidelines ensures continuous protection. Combining prevention methods may provide enhanced protection for dogs with extreme tick exposure.

Environmental management reduces tick populations and exposure opportunities. Maintaining short grass and removing brush, leaf litter, and debris eliminates tick habitat around homes. Creating barrier zones of gravel or wood chips between lawns and wooded areas reduces tick migration. Fencing to exclude deer and wildlife reduces tick hosts on properties. Professional yard treatments with appropriate acaricides can decrease tick populations. Keeping dogs out of known tick-infested areas during peak tick season limits exposure. These environmental measures supplement individual dog prevention but cannot replace it.

Behavioral modifications reduce tick acquisition during outdoor activities. Avoiding heavily wooded or brushy areas during peak tick activity periods limits exposure. Staying on cleared trails rather than walking through tall vegetation decreases tick contact. Checking dogs thoroughly for ticks immediately after outdoor activities allows removal before disease transmission, which typically requires at least several hours of attachment. Focusing tick checks on common attachment sites including ears, face, neck, between toes, and groin area improves detection. Prompt proper tick removal reduces transmission risk for attached ticks.

Health maintenance and awareness support prevention and early detection. Regular veterinary care provides opportunities for tick prevention counseling and health monitoring. Owners in endemic areas should be educated about RMSF signs and the importance of immediate veterinary evaluation for compatible symptoms. Understanding local disease epidemiology, including seasonal peaks and geographic distribution, helps owners assess risk. Maintaining current knowledge about effective tick prevention products as new options become available optimizes protection. Prompt veterinary evaluation of any febrile illness in tick-exposed dogs allows early treatment if RMSF develops.

Early intervention when exposure or symptoms occur prevents severe disease. Immediate veterinary evaluation for any dog with fever, lethargy, edema, or petechiae in endemic areas enables early treatment. Dogs with known tick exposure should be monitored closely for two weeks following exposure. Starting treatment based on clinical suspicion rather than waiting for confirmatory testing can be lifesaving. Removing attached ticks promptly using proper technique reduces transmission probability. Educating family members and caregivers about RMSF signs extends vigilance beyond the primary owner. Having a relationship with a veterinarian who understands RMSF ensures appropriate urgent response when needed.

Daily management of dogs being treated for RMSF requires careful attention to medication administration, monitoring, and supportive care. Doxycycline should be administered with food to reduce gastrointestinal upset, which is a common side effect. Dairy products near dosing time should be avoided as calcium can interfere with absorption. Medication timing should be consistent to maintain therapeutic blood levels. Dogs may initially have poor appetites; offering highly palatable foods and feeding small frequent meals encourages eating. Fluid intake should be monitored, with access to fresh water at all times. Daily observation notes improvement or deterioration in energy, appetite, edema, and any concerning symptoms.

Home environment during RMSF treatment should promote rest and recovery while allowing monitoring. Comfortable bedding in easily observed areas facilitates both rest and monitoring. Activity restriction is appropriate until clinical recovery is well established, as exertion can worsen complications. Preventing rough play with other pets or excited interactions with children protects recovering dogs. Easy access to outdoors for toileting accommodates dogs too weak for normal routines. Climate control maintains comfortable temperatures. Dogs with respiratory compromise benefit from well-ventilated, dust-free environments.

Quality of life considerations balance treatment requirements with patient comfort. Dogs recovering from RMSF may feel quite ill initially and need patient, gentle care. Minimizing stress through calm handling and familiar surroundings supports recovery. Pain management ensures comfort in dogs with joint or muscle pain. Maintaining hydration and encouraging food intake supports healing. As dogs improve, gradual return to normal activities provides mental stimulation while avoiding overexertion. Social interaction with family members reassures anxious dogs. Celebrating small improvements maintains owner morale during recovery.

Ongoing monitoring tracks recovery and identifies complications requiring intervention. Temperature monitoring, if feasible at home, helps assess fever resolution. Daily assessment of edema, bruising, and overall demeanor notes improvement or deterioration. Signs warranting veterinary contact include failure to improve within 48 hours of starting treatment, worsening symptoms, development of new neurological signs, respiratory difficulty, or evidence of bleeding. Scheduled follow-up appointments allow professional assessment of recovery progress. Post-recovery monitoring ensures complete resolution and identifies any lasting effects.

Long-term management after RMSF recovery focuses on prevention of reinfection and overall health maintenance. Implementing rigorous year-round tick prevention is essential, as recovered dogs remain susceptible to reinfection. Regular veterinary examinations monitor for any lasting effects from the illness. Dogs with residual kidney or neurological issues may need ongoing supportive care. Owner awareness of RMSF signs enables prompt response to any future illness. Connecting with the veterinary team for prevention guidance ensures optimal ongoing protection. Understanding the importance of consistent tick prevention, given the potentially fatal nature of RMSF, motivates compliance with prevention protocols.

German Shepherds have documented increased susceptibility to severe Rocky Mountain Spotted Fever, with some studies reporting significantly higher mortality rates in this breed compared to others. The reason for this increased susceptibility is not fully understood but may relate to breed-specific immune characteristics affecting response to rickettsial infection. Other purebred dogs may also have increased susceptibility compared to mixed breeds, though data is limited. Regardless of breed, any dog can develop RMSF when infected, and the disease should be considered life-threatening in all dogs. German Shepherds with suspected RMSF warrant particularly aggressive and rapid treatment given their elevated risk.

Breed-related lifestyle factors influence RMSF risk through affecting tick exposure. Working breeds commonly used for outdoor activities, including various hunting breeds, herding breeds, and sporting dogs, face elevated tick exposure through their typical activities. Dogs bred for outdoor work may spend more time in tick habitat than companion breeds. However, any dog with tick exposure in endemic areas is at risk regardless of breed. Small breeds are not protected by size; all dogs are susceptible to tick attachment and Rickettsia rickettsii infection. Mixed breed dogs have the same risk profile as purebred dogs with similar lifestyles.

Breed-specific recommendations focus on prevention and rapid response rather than different treatment approaches. All dogs in endemic areas should receive consistent tick prevention regardless of breed. German Shepherd owners should be particularly educated about RMSF signs and the critical importance of immediate veterinary evaluation for compatible symptoms. Any German Shepherd with suspected RMSF should receive immediate aggressive treatment. Breeders of German Shepherds in endemic areas may want to discuss RMSF risk with puppy buyers. Ultimately, consistent tick prevention remains the most important breed-independent recommendation for all dogs in areas where RMSF occurs.

Commonly co-occurring conditions with RMSF include other tick-borne infections acquired through vector exposure. Co-infection with multiple tick-borne pathogens occurs because the same tick may carry multiple organisms or dogs may receive bites from multiple infected ticks. Ehrlichiosis co-infection is relatively common in areas where both diseases occur. Babesiosis adds hemolytic anemia to the clinical picture if present. Lyme disease may co-occur in geographic areas with overlapping distributions. Co-infections can produce more complex clinical presentations and may require adjustments to treatment protocols. Testing for multiple tick-borne diseases is appropriate in dogs with significant exposure and atypical presentations.

Conditions producing similar symptoms to RMSF require differentiation, though treatment should not be delayed for definitive diagnosis. Ehrlichiosis and anaplasmosis cause fever, thrombocytopenia, and lethargy but typically lack the dramatic peripheral edema and rapid vasculitis progression of RMSF. Immune-mediated thrombocytopenia produces bleeding tendencies but without fever and edema. Leptospirosis shares fever, kidney involvement, and hemorrhagic potential. Disseminated intravascular coagulation from various causes can produce bleeding manifestations. Heat stroke causes acute collapse with potential coagulopathy. Doxycycline effectively treats multiple rickettsial diseases, so differentiation between RMSF and ehrlichiosis is less critical than differentiating from non-rickettsial conditions.

Potential complications of RMSF are numerous and often severe, reflecting the widespread vascular damage characterizing this disease. Neurological complications including meningitis, encephalitis, and focal neurological deficits occur with central nervous system involvement and may be permanent. Acute kidney injury from renal vessel involvement can progress to chronic kidney disease or require dialysis. Pulmonary edema and hemorrhage cause respiratory failure. Myocarditis affects heart function. Disseminated intravascular coagulation produces bleeding from multiple sites. Multi-organ failure develops in the most severe cases. Early aggressive treatment dramatically reduces complication risk, while treatment delays increase likelihood of these serious sequelae. Even with successful treatment, some dogs may have lasting effects from organ damage sustained before therapy.