Babesia and Rickettsial Disease.docx

**[Babesia and Rickettsial Disease:]** 1. **[Learning Objectives:]** Welcome to Week Two, Lesson Three of Canine Infectious Diseases. During this week we\'re going to focus on some of the tick borne diseases that we see both in the UK but also across many other countries worldwide. Simon Tappin...

**[Babesia and Rickettsial Disease:]** 1. **[Learning Objectives:]** Welcome to Week Two, Lesson Three of Canine Infectious Diseases. During this week we\'re going to focus on some of the tick borne diseases that we see both in the UK but also across many other countries worldwide. Simon Tappin MA VetMB CertSAM DipECVIM-CA FRCVS **By the end of this lesson, you should be able to:** 1. Explain the life cycle of the tick borne diseases caused by Babesia and Rickettsia species; 2. Recall the clinical signs associated with infection; 3. Discuss how to make a diagnosis of these conditions; 4. Consider the treatment options for Babesiosis and Rickettsial disease; 5. Outline the preventative strategies available. 2. **[Introduction:]** Babesiosis is a tick-borne parasitic disease which leads to infection of erythrocytes and can result in a severe, life-threatening anaemia in dogs. Simon Tappin It is particularly prevalent in France due to the presence of *Babesia canis* (with an increasing incidence in the south of the country), however tick vectors are widespread and the disease in endemic in most of Southern Europe. In early 2016, several cases of *Babesia canis* infection in dogs from the Essex area were reported that had not travelled outside of the United Kingdom.  These cases, combined with a fatal case of *Babesia vogeli* infection in an untravelled dog from Kent and unpublished reports of Babesia in untravelled dogs identified by the Acarus Laboratory in Bristol, suggest that canine babesiosis is becoming established within specific areas of the United Kingdom. 3. **[The First Reports of Babesiosis in Dogs:]** The first reports of babesiosis in dogs were made in Africa in the 1890's and since then, at least nine genetically distinct intraerythrocytic piroplasm parasites, including Babesia and the closely related Theileria and Cytauxzoon species have been identified. Babesia species are divided morphologically into the large (3-7µm in length) and small species (1-3µm in length) and the species of Babesia seen varies by geographic region, largely dependent on the tick vectors present. *Babesia canis* (previously called *B. canis canis*) is transmitted by *Dermacentor* reticulatus (the ornate cow or marsh tick) and to a lesser degree by *Rhipicephalus sanguineus* (the brown dog tick). 1. **[Dermacentor reticulatus: ]** *Dermacentor reticulatus* has historically been found in the southern parts of Europe, with 45-70% of French practices reporting confirmed infection each year. Recent work has shown that the tick vector has become established in more northerly parts of Europe, with *Dermacentor reticulatus*reported in Poland, Belgium and Germany. Milder winters have reduced tick mortality, leading to increasing tick numbers. Several studies have also documented pockets of *Dermacentor reticulatus *within the United Kingdom, mainly in west Wales, parts of Essex and the coastal areas of both North and South Devon, although until recently they were not thought to harbour *Babesia species*. The geographic incidence of *Babesia canis *infection largely mirrors the distribution of its tick vector, with outbreaks of babesiosis seen in polish sled dogs and the recent cases in the UK and Norway reflecting a northerly increase in its geographic range. 2. **[Rhipicephalus sanguineus:]** *Rhipicephalus sanguineus* is a vector for both* Babesia canis* and *Babesia vogeli*. It has a worldwide distribution in warm and humid areas, which reflects the geographic distribution of *Babesia vogeli *infection. *Rhipicephalus sanguineus* is very rarely found within the United Kingdom in association with imported animals, but it is unlikely to become endemic as climatic conditions are too cold; Defra does however acknowledge a risk of establishment within dwellings. 3. **[Babesia gibsoni: ]** *Babesia gibsoni* is a small form of *Babesia*, often associated with chronic or insidious disease and is present through most parts of the world, although rarely reported in Europe. It is transmitted by Heamaphysalis species and possibly *Rhipicephalus sanguineus*. Interestingly, a recent PCR study of 742 ticks collected from areas throughout the United Kingdom, found *Babesia gibsoni*DNA in 11 fed Ixodes ricinus ticks. Ixodes species are not a known vector for *Babesia gibsoni*, however its presence in the UK is a surprising finding, as it has not previously been documented within the UK tick population. Given its previous rare documentation in Europe, it has been suggested that its range is expanding, with two clinical cases of *Babesia gibsoni* recently reported in Germany. In the United States, where competent vectors are not endemic, *Babesia gibsoni* can be passed by direct dog to dog transmission through fighting and perinatal transmission. 4. **[Babesia rossi: ]** Clinical reports of Babesia rossi infection are mainly limited to South Africa, with over 10% of dogs evaluated in veterinary hospitals affected. It is transmitted by the yellow dog tick, Haemophysalis elliptica (previously called H. leachi) and leads to particularly virulent clinical signs. It is most commonly seen in the summer months and Bull terrier. +-------------+-------------+-------------+-------------+-------------+ | **Species** |   | **Distribut | **Tick | **Clinical | | | | ion** | Vector** | Findings** | +=============+=============+=============+=============+=============+ | *Babesia | **Large | Southern & | *Rhipicepha | Moderate | | canis* | Forms** | Central | lus | clinical | | | | Europe | sanguineus* | disease | |   | | | | | | | | | *Dermacento | Haemolytic | | | | | r | anaemia | | | | | reticulatus | Thrombocyto | | | | |  * | penia | | | | | | | | | | | | Fever | +-------------+-------------+-------------+-------------+-------------+ | *Babesia | | South | *Haemaphysa | Very | | rossi* | | Africa | lis | virulent | | | | | elliptica* | haemolytic | | | | | | anaemia  | | | | | | | | | | | | Immune | | | | | | mediated | | | | | | disease  | +-------------+-------------+-------------+-------------+-------------+ | *Babesia | | Africa, | *Rhipicepha | In affected | | vogeli* | | Asia, | lus | animals, | | | | Australia\ | sanguineus* | fever, | | | | \ | | anaemia and | | | | Central, | | thrombocyto | | | | North and | | penia | | | | South | | will be | | | | America | | present | | | | | | | | | | Northern & | | Often | | | | Central | | unapparent | | | | Europe | | clinical | | | | | | disease | | | | | | | | | | | | Young | | | | | | animals may | | | | | | have more | | | | | | severe | | | | | | signs | +-------------+-------------+-------------+-------------+-------------+ | *Babesia | **Small | USA, Asia, | *Rhipicepha | Haemolytic | | gibsoni * | Forms** | North & | lus | anaemia | | | | East | sanguineus  | | | | | Africa, | * | Thrombocyto | | | | Australia, | | penia | | | | likely | *Haemaphysa | | | | | extending | lis | Chronic | | | | through | bispinosa* | subclinical | | | | southern | | infection | | | | Europe | | leading to | | | | | | weight loss | | | | | | and | | | | | | progressive | | | | | | debilitatio | | | | | | n | +-------------+-------------+-------------+-------------+-------------+ | *Babesia | | North west | *Probably | Severe | | annea | | Spain | Ixodes | haemolytic | | (Theileria | | | hexagonus* | anaemia  | | annae)* | | | | | | | | | | A | | | | | | proportion | | | | | | develop | | | | | | renal | | | | | | failure | | | | | | | | | | | |   | +-------------+-------------+-------------+-------------+-------------+ 4. **[The Life Cycle:]** Babesiosis is transmitted when high numbers of Babesia sporozoites are passed to the host's circulation within tick saliva as the tick feeds. This happens relatively late after attachment, with the tick needing to be attached for 48-72 hours for transmission to occur. Simon Tappin These infectious sporozoites infect erythrocytes and differentiate into merozoites, allowing reproduction and the production of even more infectious merozoites. Afbeelding met tekst, Lettertype, schermopname, wit Automatisch gegenereerde beschrijving Zygotes penetrate the tick salivary gland, enabling infection of a host when the tick feeds. Within the tick's ovaries, the zygotes transform into infectious merozoites within eggs. As female ticks can produce many eggs over their lifetime (a fully fed Rhipicephalus sanguineus tick can lay over 5000 eggs in her lifetime), one infected tick may quickly become an infected population.  5. **[Clinical Signs:]** Babesia infection results in an array of clinical signs which vary between the infecting strain and species. Host factors such as age and the immunogenic response to the parasite and/or the tick vector also play a role. Simon Tappin Most clinical signs result from anaemia or the systemic inflammatory response this generates, leading to tissue dysfunction and eventually resulting in multiple organ failure. Afbeelding met paal Automatisch gegenereerde beschrijving  In addition, antibodies against normal erythrocyte and platelet targets can also be produced, leading to an immune mediated haemolytic anaemia and/or thrombocytopenia which doesn't correlate to the number of parasites present. Presenting clinical complaints are very variable and may be compounded by concurrent diseases transmitted by the tick vector, for example *Ehrlichia canis*. Acute illness with pyrexia, pallor and splenomegaly are frequently noted with *Babesia canis*infection and in severe cases, patients can present collapsed. Haemoglobinuria and bilirubinuria can also be reported secondary to excessive red cell breakdown. The systemic inflammatory response can lead to organ dysfunction and a more severe syndrome often referred to as 'complicated babesiosis', which includes acute kidney injury, hepatic dysfunction, acute lung injury, cerebral dysfunction and coagulation defects secondary to disseminated intravascular coagulation and immune mediated thrombocytopenia; these signs are also frequently associated with *Babesia rossi *infection. Compared to *Babesia canis*, *Babesia vogeli* infections are usually milder and rarely complicated, they may also be subclinical without significant haematological abnormalities. Simon Tappin 6. **[Diagnosis:]** Diagnosis of canine *Babesia* is most convincingly made by demonstrating the presence of organisms within infected erythrocytes, with *Babesia canis *usually forming pairs of pyriform organisms. Simon Tappin The level of parasitism is often low, especially in chronic cases, which can make detection difficult. Collecting blood from peripheral capillary beds with lower flow rates (e.g. the ear tip or nail bed) can yield a higher number of infected cells. Yield can also be improved by examining cells from spun microhaematocrit tubes, taken from just below the buffy coat, as the parasite is present in higher numbers in immature red cells.  PCR on EDTA anticoagulated blood is the most sensitive and specific way of diagnosing infection and also allows determination of the species present. Serology is possible and can support exposure; however, PCR and direct identification of the parasite are preferred. Haematology results will typically reveal a normocytic normochromic anaemia, which becomes regenerative a few days after infection. Afbeelding met tekst, Lettertype, schermopname, wit Automatisch gegenereerde beschrijving Autoagglutination is seen in around 20% of cases, with 85% reported to have positive Coombs test results.  Thrombocytopenia is usually not particularly severe and overt signs of bleeding are uncommon. Concurrent infection with Ehrlichia canis may worsen the risk of bleeding due to platelet dysfunction. A leucocytosis with neutrophilia and a left shift is usually present, although a moderate neutropenia has been reported in some Babesia canis cases. Biochemistry results are not specific and include elevated bilirubin, globulins and liver enzymes, with hypoglycaemia, azotaemia and marked acid-base imbalances associated with a Babesia rossi infection.  7. **[Treatment:]** Treatment for babesiosis is based on providing symptomatic supportive care and parasite clearance. Supportive care usually consists of cautious intravenous fluid therapy, with balanced crystalloid solutions to correct fluid balance, support renal function and improve acid-base imbalances. Simon Tappin Symptomatic treatment of specific clinical signs such as vomiting may require specific antiemetic therapy. In cases of severe anaemia, blood transfusions can be required. The decision to perform a transfusion is made on an individual patient basis, with it being strongly considered in any patient with a haematocrit less than 0.15l/l, or showing clinical signs associated with poor oxygen carriage and delivery (tachypnoea, tachycardia, systemic weakness, etc).  Afbeelding met tekst, schermopname, Lettertype Automatisch gegenereerde beschrijving In general, imidocarb dipropionate is suggested as the most effective drug for clearance of Babesia canis. Imidocarb is used off label under the cascade, as there is no licensed product for the treatment of canine babesiosis available in the UK, but it is readily available in an injectable format as a treatment for Babesia divergens, which causes redwater fever in cattle. If imidocarb is not immediately available, high dose clindamycin is suggested until definitive treatment can be given (25 mg/kg q12h po). Various dose regimes have been reported, but two treatments (5mg/kg) given intramuscularly 14 days apart is most commonly recommended. In general, improvement is normally seen within 24 to 72 hours of treatment, but some dogs can respond more slowly, taking up to 7 days to respond.  Imidocarb is an aromatic diamidine derivative that interferes with parasite DNA metabolism and aerobic glycolysis. It also has anticholinesterase activity, which leads to commonly seen side effects relating to stimulation of muscarinic cholinergic receptors. These include excessive salivation and lacrimation, nausea and vomiting, tachycardia, diarrhoea and unsettled or agitated behaviour. Simon Tappin Premedication with atropine (0.02-0.04mg/kg i/m) is suggested to prevent these signs occurring; an alternative strategy is to monitor closely and administer atropine (0.02mg/kg) intravenously should side effects be noted. Pain at the injection site is also commonly reported. Transient increases in liver enzymes will be seen post-administration. Acute hepatic and renal tubular necrosis are rarely reported with high doses (\>10mg/kg). It is suggested that dose reductions should be made in animals with hepatic or renal insufficiency. As imidocarb is excreted slowly, it persists in tissues and provides up to 6 weeks of protection against reinfection (Vercammen and others 1996). 8. **[Knowledge check:]** Which of the following statements are true? - **PCR is the most sensitive and specific way of diagnosing Babesiosis** - The tick vector Ixodes hexagonustransmits Babesia canis - **With Babesia infection, haematology results typically reveal a normocytic normochromic anaemia initially which later becomes regenerative. ** - Babesiosis infects granulocytes - Clindamycin is the most effective drug for the clearance of Babesia canis - **For the transmission of Babesiosis, the tick needs to be attached for 48-72 hours** - **Collecting blood from the ear tip or nail bed can improve the diagnosis of Babesiosis on a blood smear** 9. **[History:]** Let's have a look at what Babesia infection looks like in a clinical case. Simon Tappin This is Harry, a 10-year-old neutered male crossbreed dog. He presented as an emergency for further evaluation of lethargy, depression and marked haematuria. The dog had become listless 24 hours after returning with his owners from a two-week vacation near Toulouse in France. During this time, several ticks had been removed, the last one was removed seven days before returning to the UK. No ectoparasite prevention had been used during the trip.   10. **[Clinical Signs:]** At presentation, the dog was dull and depressed but in good body condition. Clinical examination revealed pale mucous membranes, bounding peripheral pulses and a moderate tachycardia. Simon Tappin Afbeelding met zoogdier, orgaan, huid, hond Automatisch gegenereerde beschrijving Mild peripheral lymphadenopathy was detected and marked splenomegaly was evident on abdominal palpation. Moderate pyrexia was present (40°C) and several *Dermacentor reticulatus*were also present. At this stage, the pale mucous membranes, increased heart rate and bounding pulses suggested the dog was anaemic, with the pyrexia and lymphadenopathy suggesting an inflammatory response. Given the recent history of travel and the presence of unusual ticks on Harry, imported disease was considered. Simon Tappin 11. **[Diagnostic Testing:]** The dog was admitted and blood samples were taken. Simon Tappin 5. **[PCV:]** A spun microhaematocrit tube revealed the dog to be moderately anaemic (PCV 20%) with evidence of haemolysed serum.  Which differential diagnoses would you consider for haemolysis? Simon Tappin ------------------------------------------------------------------------------------------------------------ **Causes of Canine Haemolysis** --------------------------------- -------------------------------------------------------------------------- Mechanical damage Haemangiosarcoma\ Vasculitis\ Disseminated intravascular coagulation\ Heart valve disease Toxins Onion\ Garlic\ Paracetamol (Acetaminophen)\ Zinc\ Naphthalene Immune-mediated destruction Primary immune-mediated haemolysis\ Secondary immune-mediated haemolysis (e.g. drugs, neoplasia, infection)\ Neonatal isoerythrolysis\ Transfusion reactions Inherited disease Osmotic fragility syndrome\ Phosphofructokinase deficiency\ Pyruvate kinase deficiency Infectious disease Mycoplasmosis\ Babesiosis\ Leptospirosis Miscellaneous Hypophosphataemia\ Haemolytic uraemic syndrome ------------------------------------------------------------------------------------------------------------ 6. **[In-saline Aggluttination Test:]** An in-saline agglutination test revealed marked macroscopic agglutination. Microscopic examination excluded rouleaux formation. Simon Tappin Afbeelding met verven, aquarium, vis, overdekt Automatisch gegenereerde beschrijving The presence of anaemia with agglutination and haemolysis, is very suggestive of immune-mediated haemolytic anaemia, however, given the history of travel, Babesia infection was a very likely differential diagnosis.  7. **[Blood Smear:]** A smear was carefully examined for the presence of *Babesia*organisms. Moderate numbers of pyriform intracellular organisms were found. PCR later confirmed these to be *Babesia canis.* Simon Tappin  8. **[Complete Blood Count and Biochemistry:]** A complete blood count also indicated a mild neutrophilia and monocytosis, consistent with an inflammatory response. A moderate thrombocytopenia was present, however a coagulation screen (PT, APTT and D-dimers) was normal. Biochemistry revealed a mild azotaemia, but was otherwise unremarkable.  9. **[Urinalysis:]** A free-catch urine sample revealed marked discolouration and analysis revealed the presence of both free haemoglobin and a smaller number of intact red cells. The specific gravity was high (1.042), suggesting the azotaemia documented was pre-renal. PCR for concurrent Ehrlichia and Leishmania was negative. 12. **[Treatment:]** Harry was admitted and placed on intravenous fluid therapy (lactated Ringer's solution, 10 ml/kg bolus then twice maintenance). Fluid therapy was given to support circulating fluid volume and to promote the excretion of haemoglobin. Simon Tappin The dog was treated with imidocarb (5mg/kg IM) in order to eliminate the parasites. As concurrent infection with *Ehrlichia *is reported in *Babesia *cases, treatment with doxycycline (10mg/kg q24h) was commenced until negative *Ehrlichia *PCR results were obtained. Doxycycline has also been shown to reduce the level of parasitaemia in dogs already on treatment at the time of *Babesia *infection.   The owners' other dog had also travelled with the patient to France. Although this dog had not developed clinical signs, several ticks had also been found and removed ten days previously. PCR for *Babesia *was negative in this dog, however clindamycin (25mg/kg q12h) was prescribed until these results became available. Over the course of the next 24 hours, Harry's demeanour worsened and he started to vomit. A repeat PCV revealed that Harry's anaemia had worsened (PCV 14%), marked agglutination was still present and a moderate number of spherocytes were detected, indicating immune-mediated erythrocyte destruction. Simon Tappin Although the PCV drop may have been partly due to haemoconcentration at Harry's initial presentation, the presence of spherocytes and marked agglutination suggested continued red cell destruction. A single injection of dexamethasone was given (0.4 mg/kg/IV) and an improvement in the PCV followed over 48 hours.   Abdominal ultrasound was performed to investigate the cause of the vomiting; this was unremarkable. As pancreatitis is a frequent complication of babesiosis, a cPLi was performed; this was normal, suggesting pancreatitis was unlikely. The vomiting responded well to maropitant (1 mg/kg/SC) and was felt to be a side effect of the imidocarb. The dog made a good recovery and was discharged on day four. At this point, Harry's PCV had improved to 24%, the thrombocytopenia had resolved and no *Babesia *organisms were seen on smear evaluation. Harry returned ten days later, with his owners reporting he had returned to full health. At this stage, clinical examination was unremarkable. Haematology revealed a complete resolution of the anaemia and thrombocytopenia and no evidence of agglutination or parasitaemia was present. A second injection of imidocarb (5 mg/kg/IM) was given 14 days after the first. To prevent the vomiting seen after the first treatment, an injection of maropitant was given as an antiemetic. Repeat PCR for Babesia was negative. A further Babesia PCR was negative four weeks later, with the dog making a full recovery and remaining clinically well. 13. **[Prevention:]** Preventing tick attachment, or killing ticks before disease transmission occurs, are the best methods of reducing the risk of canine babesiosis.  A number of different topical products have been shown to have good activity in preventing tick attachment and long acting oral treatments are available that kill any ticks that attach over prolonged time periods. Simon Tappin  Regular use of these products should be suggested to all owners of dogs walked regularly in areas with high tick numbers, especially at high risk times of the year (autumn and spring) and in areas with a risk of possible canine babesiosis. As transmission of *Babesia *species classically does not occur until 48 hours after tick attachment, prompt removal of the ticks will limit transmission. Afbeelding met tekst, Lettertype, schermopname, lijn Automatisch gegenereerde beschrijving In general, canine *Babesia *species do not appear to pose a zoonotic risk, however rare cases of human babesiosis have been reported in immunosuppressed, elderly and splenectomised patients. Immunosuppressed or splenectomised individuals should therefore exercise caution in removing ticks and handling blood samples from animals infected with *Babesia *species. 14. **[Introduction to Rickettsial Disease:]** Rickettsiae are intracellular organisms which cause disease by affecting the function of their target cells, which are mainly white cells and platelets. Infection leads to clinical signs associated with deficiencies and dysfunction of the affected cell lines.  Rickettsiae are classified within α-proteobacteria and include the genera of *Ehrlichia* (which includes *Ehrlichia canis*) and *Anaplasma*(which includes *Anaplasma phagocytophilium*). Simon Tappin The nomenclature of rickettesial diseases can be confusing, as recent advances in DNA sequencing allowed reclassification of the order Rickettsiales in 2001, leading to some organisms changing their names. Also historically, individual organisms have been named by the genus of the infectious agent, the species it affects and its predominant target cell \[for example, *Ehrlichia canis *leading to canine monocytotrophic ehrlichiosis\], whereas with the advent of molecular testing, the genus and species responsible can be much more easily defined, creating less confusion as to the responsible infectious agent.  10. **[Distance tree of *Anaplasma* and *Ehrlichia* species:]**  Ehrlichia and Anaplasma are tick-borne diseases and are limited to the geographic location of the vector. *Ehrlichia canis* is the most common rickettsial disease seen in Southern Europe, but is not currently considered endemic in the United Kingdom. *Anaplasma phagocytophilum* has been isolated in Ixodes ticks within the United Kingdom, but is rarely associated with clinical disease. Simon Tappin +-------------+-------------+-------------+-------------+-------------+ | **Species** | **Distribut | **Cells**\ | **Tick**\ | **Disease** | | | ion** | **infected* | **Vector** | \ | | | | * | | **reservoir | | | | | |  ** | +=============+=============+=============+=============+=============+ | *Ehrlichia | Temperate | Monocytes & | Rhipicephal | Wild & | | canis* | and | Macrophages | us | domestic | | | tropical | | sanguineus | canids | | (Canine | areas | | | | | monocytotro | worldwide, | |   | | | pic | except | | | | | ehrlichiosi | Australia | |   | | | s) | | | | | | |   | | | | +-------------+-------------+-------------+-------------+-------------+ | *Ehrlichia | Southern | Monocytes, | Numerous | White-taile | | chaffeensis | parts of | Macrophages | ticks | d | | * | the United | , | including | deer, | | | States  | Neutrophils | Amblyomma | coyotes, | | (Human | | & | americanum | racoons, | | monocytotro | | Lymphocytes | | voles | | pic | | | | | | ehrlichiosi | | | | | | s) | | | | | +-------------+-------------+-------------+-------------+-------------+ | *Ehrlichia | Midwest and | Granulocyte | Amblyomma | Wild & | | ewingi * | Southern | s | americanum  | domestic | | | United | | | canids | | (Granulocyt | States  | | | | | ic | | | | | | erhlichiosi | | | | | | s) | | | | | +-------------+-------------+-------------+-------------+-------------+ | *Anaplasma | Worldwide, | Granulocyte | Idoxes spp. | White-taile | | phagocytoph | mainly | s | | d | | ilum*  | temperate | |   | deer, mice, | | | and | | | voles & | | (Granulocyt | northern | | | migratory | | ic | areas | | | birds  | | anaplasmosi | | | | | | s) | | | | | +-------------+-------------+-------------+-------------+-------------+ | \* Anaplasm | Worldwide | Thrombocyte | Likely: | Canids & | | a | | s | Rhipicephal | small | | platys * | | | us | ruminants | | | | | sanguineus | | | (Thrombocyt | | | | | | otrophic | | | | | | anaplasmosi | | | | | | s) | | | | | +-------------+-------------+-------------+-------------+-------------+ 15. **[Introduction to Ehrlichiosis:]** *Ehrlichia canis*, the causal agent of canine monocytotrophic ehrlichiosis, is a small, pleomorphic gram-negative intracellular rickettsial parasite. It appears as round intracytoplasmic inclusions within monocytes and macrophages. Simon Tappin Afbeelding met schimmel Automatisch gegenereerde beschrijving  It was first described in Algeria in 1935, but did not gain prominence until the Vietnam War, when many American service German shepherd dogs, (which are highly susceptible to *Ehrlichia canis* infection \[or tropical canine pancytopenia as it was known at the time\]), died as a result of the disease. It also received publicity when it was confused as the cause of human monocytotrophic ehrlichiosis in the late 1980's, until *Ehrlichia chaffeensis* was discovered as the cause. Simon Tappin 16. **[Epidemiology:]** *Ehrlichia canis* infection is found worldwide in temperate and tropical areas, with the exception of Australia. The areas where canine *Ehrlichia canis *infection are reported mirrors the geographic distribution of its vector. Simon Tappin Which of the following is the main vector for Ehrlichia canis? - Ixodes ricinus  - Haemaphysalis elliptica - Dermacentor reticulatus - **Rhipicephalus sanguineus** *Rhipicephalus sanguineus* (the brown dog tick) is the main vector for *Ehrlichia canis* In Europe, accurate information on the disease prevalence is not available; however cases are particularly concentrated around the south coast of France, Corsica, Greece and the southern half of Italy. Simon Tappin Although *Ehrlichia canis* is not currently considered endemic in the United Kingdom, dogs are occasionally imported with the disease and recent cases in untravelled dogs have been reported. **JSAP Case Report; *Ehrlichia canis* infection in a dog with no history of travel outside the United Kingdom Wilson and others 2013.** [**VIEW REPORT(OPENS IN A NEW TAB)**](https://onlinelibrary.wiley.com/doi/abs/10.1111/jsap.12088) What is the reservoir for *Ehrlichia canis*? Simon Tappin - **Wild and domestic dogs ** - Small ruminants - Rodents - Migratory birds The reservoir for *Ehrlichia canis* infection is in wild and domestic dogs. Its vector *Rhipicephalus sanguineus* has a single host preference and feeds on dogs at all three stages of its life cycle. Experimentally, the American dog tick Dermacentor variabilis has also been shown to transmit infection.  Ehrlichia canis is passed to the next stage but is not passed on transovarially in the tick, so unexposed ticks must feed on an infected dog in the acute phase to become infected.  After attachment, Ehrlichia transmission may be rapid, with experimental studies showing this can occur as early as 3 hours post-exposure. 17. **[Clinical Signs:]** Once infected, the incubation period is reported as 8-20 days and the organism spreads throughout the body multiplying in macrophages. Three phases of ehrlichiosis are seen; acute, subclinical and chronic. 11. **[Acute Ehrlichiosis:]** The acute phase usually lasts 1-4 weeks and most dogs recover with appropriate treatment. Affected dogs typically have non-specific signs, such as fever, anorexia and lymphadenomegaly. Haematology results usually reveal thrombocytopenia, leucopenia and anaemia.  The dogs below have cutaneous petechial haemorrhages as a result of thrombocytopenia in the acute stages of Ehrlichia. Simon Tappin Afbeelding met Vlees, hond, persoon Automatisch gegenereerde beschrijving Ocular signs are often seen in the acute stages of Ehrlichiosis. Corneal opacity (due to oedema and/or deposition of cellular precipitates), anterior uveitis, hyphaema, tortuous retinal blood vessels and focal chorioretinal lesions are commonly reported. Subretinal haemorrhages resulting in retinal detachment may occur and lead to blindness.  12. **[Subclincal Ehrlichiosis:]** Untreated dogs, or those that do not fully clear the organism may enter a subclinical state where they become asymptomatic carriers for months to years.  13. **[Chronic Ehrlichiosis:]** Persistently infected dogs may spontaneously clear *Ehrlichia*, however in some dogs, the organism persists leading to chronic infection. Not all dogs develop signs of chronic disease and why this occurs is not clear, but it appears to be more common in German shepherd dogs. GSD with epistaxis caused by chronic infection GSD with epistaxis caused by chronic infection  The spleen and its mononuclear phagocytic system seem important in determining pathogenesis and in experimental animals, splenectomised dogs show less severe clinical signs. Simon Tappin Chronic infection leads to bone marrow hypoplasia and resultant pancytopenia. Thrombocytopenia and platelet dysfunction can lead to severe bleeding in some cases (submucosal haemorrhage and epistaxis). The prognosis associated with chronic *Ehrlichia canis *infection is very guarded. In this phase, biochemistry will usually reveal a marked increase in globulins.  This increase in globulins is usually polyclonal, although occasional monoclonal increases have been reported and hyperviscosity associated with clinical signs such as retinal detachment have been occasionally seen.  18. **[Diagnosis:]** Identification of *Ehrlichia *morulae in leucocytes is diagnostic, but can be difficult and is time-consuming. Blood collected from a peripheral capillary vessel such as the ear margin, or buffy coat analysis are most rewarding. Morulae have also been reported in macrophages found within lymph node and lung aspirates. Simon Tappin  Afbeelding met tekst, Lettertype, schermopname, wit Automatisch gegenereerde beschrijving Using serology, a rising titre of a fourfold increase over a two week period confirms active infection. Several commercial ELISA tests are also available and are useful for patient-side use, however, cross-reaction and false-positive results can occur if the patient has been exposed to less pathogenic rickettsiae (this is much less of a problem in Europe than in the United States). Diagnosis can be made on the basis of PCR, which is very sensitive and effective at confirming that animals have cleared the infection after treatment.  19. **[Treatment:]** Which of the following is the treatment of choice for Ehrlichiosis? Simon Tappin  - Imidocarb dipropionate - **Doxycycline** - Enrofloxacin - Chloramphenicol Doxycycline is the treatment of choice (5mg/kg q12hrs PO or 10mg/kg q24hrs for 21 days) and generally leads to a clinical improvement within 1-3 days. Imidocarb has been suggested for use in resistant infections, however experimental work has shown it to be ineffective at clearing* Ehrlichia canis* infection. Chloramphenicol should be used in these instances (25-50mg/kg q8hrs PO for 21-28 days). Chloramphenicol has also been suggested in puppies younger than five months due to the risk of tetracycline leading to enamel staining of teeth. Why might we want to use chloramphenicol in these cases? Think about this and continue to reveal the answer.  Simon Tappin The answer is due to the risk of tetracycline leading to enamel staining of teeth. 20. **[History:]** Let\'s have a look at a second case.\ \ This is Paddy, a 4-year old female neutered Labrador who presented with acute onset blindness and ocular discomfort. Paddy had been on holiday in Spain 6 months previously and had a history of gradual weight loss. Simon Tappin Afbeelding met gras, buitenshuis, Hondenras, huisdier Automatisch gegenereerde beschrijving 21. **[Ocular Examination:]** Evaluation by an ophthalmologist revealed bilateral uveitis and intraocular haemorrhage. Treatment for the uveitis with a topical steroid was started and an evaluation was initiated  to look for an underlying systemic disease that could have triggered the uveitis. Simon Tappin  22. **[Laboratory Investigations:]** Biochemistry revealed markedly increased globulins which were monoclonal on serum electrophoresis. Haematology revealed a pancytopenia with a non-regenerative anaemia, neutropenia and thrombocytopenia. Simon Tappin Above is the SPE gel for Paddy. Serum and urine have been applied to the gel on the right side of the screen and migrate with the current towards the left. The smallest proteins get furtherest which is albumin and the largest are the globulins which are on the right - both serum and urine globulins are elevated in a very narrow spike which is a similar width to the albumin. This is a monoclonal spike, which usually seen either with lymphoproliferative disease or the response to infection. Above is the SPE gel for Paddy. Serum and urine have been applied to the gel on the right side of the screen and migrate with the current towards the left. The smallest proteins get furtherest which is albumin and the largest are the globulins which are on the right - both serum and urine globulins are elevated in a very narrow spike which is a similar width to the albumin. This is a monoclonal spike, which usually seen either with lymphoproliferative disease or the response to infection.  14. **[Diagnosis:]** Given these findings, a bone marrow based disease was suspected (most likely a lymphoproliferative disease such as lymphoma), however as the dog had recently travelled to Spain, an Ehrlichia PCR was performed and the result was positive.  15. **[Treatment:]** The dog was treated with doxycycline and had a very good response. The uveitis resolved upon treatment of the underlying disease and the haematological parameters gradually returned to normal. 16. **[Knowledge Check:]** Ehrlichia transmission can occur as early as how many hours after tick attachment?  - **3 hours** - 5 hours - 12 hours - 24 hours Which breed of dog seems susceptible to developing chronic infection with Ehrlichia? - Springer spaniel - Golden retriever - **German shepherd dog** - Labrador retriever Microscopy of a blood smear can reveal *Ehrlichia *morulae in which cells?  - Reticulocytes  - Macrophages  - **Monocytes** - Leucocytes How long does the acute phase of ehrliciosis typically lasts? - 4-8 weeks  - **1-4 weeks ** - 7 days - 1-2 weeks 23. **[Anaplasma phagocytophimul and Anaplasma platys:]** 17. **[Anaplasma Phagocytophilum: ]** *Anaplasma phagocytophilum *(previously named *Ehrlichia phagocytophilum*), *Ehrlichia equi* and *Cytoecetes phagocytophilia*, all cause granulocytic ehrlichiosis. First reported in the Scottish sheep in the 1930's, it was reported as the cause of pasture fever in cattle in England in the 1950's and in Finland a decade later. The first canine cases were reported in the 1980's in Switzerland, Sweden and North America, and feline cases were reported in Sweden in the late 1990's.    Diagnostic evaluation may reveal *Anaplasma *inclusion bodies within neutrophils, accompanied by mild to marked neutropenia and thrombocytopenia. PCR for *Anaplasma *performed on whole EDTA blood is commonly available and is more sensitive than direct microscopy.  Treatment with doxycycline (10mg/kg q12hrs PO for 10-21 days) is usually successful and steroids may need to be considered if immune-mediated disease is present. Simon Tappin 18. **[Anaplasma Platys:]** *Anaplasma platys* (previously known as *Ehrlichia platys*), has a tropism for platelets and leads to canine cyclic thrombocytopenia. It was first reported in the United States in 1978 and since then has been reported in much of the world including southern Europe and the Mediterranean basin, Southeast Asia, South America, Africa and Australia. Although its mode of transmission has not been fully detailed, it is believed to be transmitted by *Rhipicephalus sanguineus*, which is supported by its geographical distribution and reported co-infection with *Ehrlichia canis*, although this has not yet been definitively proven by experimental transmission studies. Simon Tappin Afbeelding met paars, violet, Kinderkunst, Kleurrijkheid Automatisch gegenereerde beschrijving  This is followed by a period of profound thrombocytopenia, with the platelet counts often dropping below 20x109/l as a result of direct injury to the platelets and the associated immune response. Platelet levels return to normal over 3-4 days. Cyclical episodes of thrombocytopenia then occur at 7-14 day intervals. The levels of parasitaemia become less marked over time; however the thrombocytopenia is often marked, suggesting an immune-mediated mechanism during later episodes.  There are geographical variations in the strains of *Anaplasma platys* and therefore differences in the reported clinical signs. In the United States, minimal clinical signs post-infection are reported, however in the Mediterranean area, severe cyclical episodes of bleeding such as epistaxis have been reported. Co-infection with *Babesia canis* or *Ehrlichia canis* may lead to more pronounced clinical signs. Simon Tappin Diagnosis is usually made by microscopic detection of the organism; however serology and PCR tests are also available. Treatment with doxycycline (10mg/kg q12hrs po for 10 days) or enrofloxacin (5mg/kg q24hrs po for 21 days) have been shown to clear infection. 24. **[Prevention of Rickettsial Disease:]** The best method of reducing the risk of rickettsial disease is to prevent ticks from attaching, or killing and removing ticks quickly when they do attach.  Some molecules such as permethrin have a repellent effect against ticks, whilst others such as fipronil or the isoxazolines (e.g. afoxolaner) are fast acting acaricides. Simon Tappin Afbeelding met insect, leider, maatstok, ongedierte Automatisch gegenereerde beschrijving  As any acaricide will not be 100% effective in preventing tick attachment, owner vigilance and prompt tick removal using a tick hook will further reduce the risk of tick-borne disease transmission. This will help reduce the risk of Anaplasma infection which is thought to take 24-48 hours to be transmitted after tick attachment, however, may be less effective against *Ehrlichia canis*, which can occur very rapidly after tick attachment.  25. **[Completion of Online Learning:]** You have now completed Week Two, Lesson Three of Canine Infectious Diseases. Simon Tappin **To recap the learning objectives, you should now be able to:** 1. Explain the life cycle of the tick borne diseases caused by Babesia and Rickettsia species; 2. Recall the clinical signs associated with infection; 3. Discuss how to make a diagnosis of these conditions; 4. Consider the treatment options for Babesiosis and Rickettsial disease;