TICK-BORNE DISEASES
KEY POINTS
- Parasites (protozoa or bacteria) transmitted through ticks and insects
- Cases are increasing in the United Kingdom
- May cause severe and fatal disease
- Testing imported dogs is important
- Common parasites include Babesia , Ehrlichia, Borrelia, Anaplasma, Hepatozoon
Small protozoan parasite that is transmitted through tick bites.
Epidemiology
Babesia spp. are generally highly host specific with regards to the tick species and the mammalian host. Babesia canis is the most important in Southern Europe and there is at least one endemic area now in the United Kingdom. Other types may affect cats, horses, cattle, humans and wildlife.
Pathophysiology
Sporozoites infect the red blood cells. Here they differentiate in to merozoites and divide by binary fission causing cell lysis.
Clinical signs
Anaemia then occurs which can be severe and life threatining. Organ failure, red-coloured urine, anorexia, vomiting, fever, arthritis, myositis and jaundice, may also occur.
Diagnosis
Blood smears, serology and molecular diagnosis have been used for diagnosis.
Polymerase chain reaction (PCR) has been proven to be higher than blood smear examination, especially for the diagnosis of chronically infected dogs but false negative results cannot be completely excluded.
Treatment
Chemotherapy should be initiated as soon as diagnosis confirmed.
Prevention
Effective tick-control.
Vaccination can prevent severe disease, but not infection.
Chemoprophylaxis can prevent disease but not infection and may be an option for splenectomised or immunocompromised dogs spending short periods of time in endemic areas.
Zoonosis
Infections with Babesia spp. of dogs and cats have not been reported in humans.
ANAPLASMOSIS
Gram negative bacteria that infects its host through tick bites.
Epidemiolgy
Anaplasma phagocytophilum (previously Ehrlichia phagocytophila) and Anaplasma platys have been reported in dogs. They infect white blood cels (A. phagocytophilum) or platelets (A. platys) following transmission. A. phagocytophilum transmission occurs thorugh the tick (Ixodes) bite, whereas transmission of A. platys is thought to be ticks and other arthropods. Feeding is usually necessary for 24-48h for transmission to occur.
Pathophysiology
A. phagocytophilum develops by binary fission in to morulae in the phagosomes (neutrophils and eosinophils).
A. platys infections affect the platelets which causes cyclic thrombocytopaenia
Clinical signs
Canine granulocytic anaplasmosis is caused by A. phacocytophilum. Cyclic thrombocytopaenia occurs with A. platys.
Non-specific signs can be seen with both species of Anaplasma, including inappetence, lethargy, fever, anorexia, petechiae (surface bleeding), tachypnoea (fast breathing) and enlarged lymph nodes. A. phagocytophilum signs may include lameness (polyarthritis), diarrhoea and vomiting. More rarely, cough, uveitis, polyuria, polydipsia and limb oedema.
Diagnosis
Blood smears, serology, rapid antigen tests, ELISA and molecular diagnosis have been used for diagnosis.
Specialised laboratories are offering Polymerase chain reaction (PCR) which can confirm infection. Nagative results do not completely rule out infection.
Treatment
Antiricketssial agents are used to treat anaplasmosis, alomng with complimentary treatment.
Prevention
Effective tick-control.
Zoonosis
Human anaplasmosis has been reported. Transmission is from infected ticks. Direct transmission from dogs has not been reported.
BORRELIOSIS (LYME)
Bacteria (spirochaete) that infects its host through tick bites.
Epidemiolgy
Borrelia burgdordfeli can infect and cause disease in dogs and humans. There are reports of infections in cats but there is very little data and it is porrly understood. Other mammals and birds can act as reservoirs.
Ticks (Ixodes) are recognised as the disease vectors.
Lyme borreliosis is distributed throughout Europe, except from the more extreme hot Southern or Northern areas.
Clinical signs
Dogs often present with fever, lameness, myalgia and lethargy. Lyme arthropathy or polyarthritis may occur and there have been reports of a protein losing nephropathy. Clinical signs in cats are uncommon.
Diagnosis
Following a tick bite, the bacteria can be found in soft tissues, rather than in blood or urine, making diagnosis by PCR difficult. Antibodies against Borrelia usually appear after 3-5 weeks after infection and can be detected on immunochromatograhic tests. Positive results indicate exposure and not necessarily clinical disease.
Seroloogically positive dogs can lead to misdiagnosis or unnecessary treatment of dogs that may never develop Lyme disease.
Treatment
Targetted antibiotic therapy can resolve clinical symptoms but studies have shown infections are not cleared in all dogs.
Prevention
Effective tick-control - awareness often increased when a dog is seropsitive.
Vaccines are still contraversial.
Zoonosis
Dogs and cats are not reservoirs of Borrelia burgdorferi, whereas ticks may carry the pathogen that can be passed on to humans.
HEPATOZOONOSIS
Hepatozoon canis is a protozoan parasite that can infect dogs following a tick bite or ingestion.
Epidemiology
The tick (Rhipicephalus sanguineus) infects the host fowllowing tick ingestion or a bite. Dogs and foxes can be infected. Cases are reported mainly in Southern Europe and in imported dogs.
Clinical signs
Most disease processes are subclinical or mild.
Diagnosis
White blood cells can be examined on blood smears with a relatively high sensitivity. Serology and PCR can also be performed.
Treatment
Combination therapy is generally used. Infections are generally relatively easy to treat.
Prevention
Effective tick-control. and hunting reduction (reduce ingestion of ticks).
Zoonosis
Hepatozoon is not a zoonotic disease.
EHRLICHIOSIS
Ehrlichia canis is a bacterial parasite that is transmitted by ticks.
Epidemiology
The main host is the dog, although other canids can serve as reservoirs, and transmission is through tick (Rhipicephalus sanguineus) bites. Infections in cats have been reported but are considered rare and still not well described. Transmission thorugh blolod transfussions has also been described.
Countries with reported cases incluse, Italy, Portugal, Spain, Switzerland, Greece, Germany, France and the United Kingdom.
Pathophysiology
White blood cells (lymphocytes and monocytes) are infected and the typical morula stage develops.
Clinical signs
These may include apathy, weakness, weight loss, fever, splenomegaly, lymphadenopathy, peripheral oedema, haemorrhages, epistaxis, blindness, haematuria, pneumonia, arthritis (lameness), seizures, ataxia, amongst others.
Diagnosis
Blood smears, serology and molecular diagnosis have been used for diagnosis. Blood smears rarely show the morulae in the white blood cells. Serology can be negative initially for weeks.
Polymerase chain reaction (PCR) can confirm infection, although a negative results cannot exclude infection.
Treatment
Treatment with antirickettsial agents is possible and often successful.
Prevention
Effective tick-control.
Zoonosis
Infections have not been reported in humans.
