Leishmania and Dirofilaria.docx

**[Leishmania and Dirofilaria:]** 1. **[Learning Objectives:]** Welcome to Week Three, Lesson One of Canine infectious Diseases. In this lesson, we\'re exploring two global parasites transmitted by insect vectors. These are endemic in many regions of the world and diagnosed regularly in these co...

**[Leishmania and Dirofilaria:]** 1. **[Learning Objectives:]** Welcome to Week Three, Lesson One of Canine infectious Diseases. In this lesson, we\'re exploring two global parasites transmitted by insect vectors. These are endemic in many regions of the world and diagnosed regularly in these countries. For regions where the parasites are not endemic, they should be considered in patients presenting unwell after international travel. Simon Tappin MA VetMB CertSAM DipECVIM-CA FRCVS  **By the end of this lesson, you should be able to:** 1. Review the aetiology and pathophysiology of Leishmania and Dirofilaria; 2. Recall the clinical signs associated with Leishmania and Dirofilaria; 3. Outline how to make a diagnosis of Leishmania and Dirofilaria; 4. Consider the treatments options for dogs with Leishmania and Dirofilaria; 5. Reflect on preventative strategies. 2. **[Leishmaniasis:]** Leishmaniasis is a serious and fatal protozoan disease of dogs (and occasionally cats), and is endemic throughout South America, the Middle East and the Mediterranean areas of Europe. Simon Tappin  In southern Europe, Leishmania infantum is the causative species and is carried by its **vector** the Phlebotomus sand fly. The specific habitat and climate requirements for the sand fly vector limits endemic Leishmaniasis to southern Europe. It is estimated that at least two and a half million dogs have Leishmaniasis in south west Europe and climate change is allowing the vector and the disease to move slowly northwards. Although the risk of **zoonotic infection** is low, sand flies are considered the main route for L. infantum transmission to people from dogs and wild canids. Children and immunosuppressed adults (such as those with HIV), are particularly susceptible. Afbeelding met ongewerveld dier, ongedierte, Macrofotografie, geleedpotige Automatisch gegenereerde beschrijving Here are some key facts about Leishmaniasis. - 50% of DACTARI cases relate to Leishmaniasis. DACTARI is the dog and cat travel risk information scheme in the UK.  - Southern Europe - Disease mainly of dogs - Transmitted by Sand flies - Phlebotomus spp - Dog to dog - **Zoonotic** - rarely reported dog to human transmission - Care in immunosuppressed owners - Concurrent Ehrlichia infection is common  3. **[Epidemiology:]** Sand flies are not present within the United Kingdom (UK); however, reported cases of canine leishmaniasis are increasing as a result of animals travelling to and being imported from, endemic areas in Europe. Since the introduction of the Pet Travel Scheme (PETS) in 2000, large numbers of dogs have entered the UK under the scheme. Although PETS is designed to keep the UK free from rabies and *Echinococcus multilocularis*, there is no statutory requirement for preventative measures to be taken against exotic disease during travel. Similarly, leishmaniasis is not notifiable in the UK and the prevalence of the disease in dogs entering the UK is largely unknown. Simon Tappin  A national reporting scheme known as DACTARI (Dogs and Cat Travel and Risk Information) was set up by Defra in March 2003, allowing surveillance of exotic disease (including leishmaniasis) and to date, 51 cases of leishmaniasis have been reported. However, this scheme was voluntary and did not accurately reflect the number of cases seen, so is no longer functional. A study reviewing cases with a laboratory diagnosis of leishmaniasis around the same time, documented 257 cases in the UK over the three year period between 2005-2007 (Shaw et al, 2009). The majority of these dogs had spent at least six months in an endemic area (96%), with the most commonly reported countries of origin being Spain (57%), Greece (14%), Portugal (9%) or Italy (9%). We don't have a recent study to understand the prevalence of leishmania in the UK at present, but it is becoming an increasingly reported disease.  Worryingly, two cases of leishmania have been reported in un-travelled dogs which were **co-housed** with infected imported animals and three dogs obtained from UK rehoming centres were confirmed to have leishmaniasis having had **no history of travel**. Last year, the RVC also reported leishmaniasis in a dog that had not travelled to an endemic area (see link below). Mechanical dog to dog transmission or another as yet undetermined vector, is postulated as the route of transmission in these cases. Simon Tappin  **RVC diagnoses first case of leishmaniosis transmission between dogs in the UK ** [**CLICK HERE(OPENS IN A NEW TAB)**](https://www.rvc.ac.uk/news-and-events/rvc-news/rvc-diagnoses-first-case-of-leishmaniosis-transmission-between-dogs-in-the-uk) 4. **[Life Cycle:]** The life cycle involves the sand fly and a vertebrate host. Simon Tappin  Female sand flies harbour Leishmania promastigotes in their gut and transmit them during feeding. These promastigotes are injected with saliva into the host's skin, where they are phagocytosed by **macrophages**. Within the macrophage, multiplication occurs by **binary fission** to amastigotes. Division ruptures the macrophage, freeing amastigotes to **penetrate adjacent cells** and **disseminate** to the **visceral organs**. The cycle is completed when cells containing amastigotes are taken up by the sand fly during feeding. Amastigotes transform into promastigotes and multiply, ready to be injected into a naïve host. Vertical transmission in utero is reported and in North America,* L. infantum *has been transmitted between dogs via **blood transfusion**. Afbeelding met tekst, grafische vormgeving Automatisch gegenereerde beschrijving 5. **[The Outcome of Leishmania Exposure:]** **Not** all dogs that are infected with Leishmania will develop clinical signs. Simon Tappin  The **immune response** mounted by the dog determines whether the infection will be cleared, whether generalised symptoms develop or when the infection progresses from an asymptomatic to a symptomatic state. Studies in endemic areas show 60-70% of dogs are infected with Leishmania, but the **prevalence** of disease is much **lower**, around **10%**. There appear to be **two peaks in age** prevalence in dogs; those less than **three years old** and those around **eight to ten years old**.  Whether dogs develop clinical signs or not depends largely on their **immune response**. Simon Tappin  Afbeelding met tekst, schermopname, cirkel, diagram Automatisch gegenereerde beschrijving In the activity below, drag the words into the correct boxes to complete the paragraph. Simon Tappin   6. **[Clinical Signs:]** Classic signs of Leishmania follow a very **chronic** and often **variable course**. **Clinical signs** may occur **many years after infection** -- this can be difficult when dogs are imported into the UK for example, as unless you dig back into the history, it may not be apparent that the dog was imported from an endemic area many years previously. Simon Tappin  Afbeelding met zoogdier, Hondenras, huisdier, hond Automatisch gegenereerde beschrijving **Clinical signs** and **historical findings** can also be very varied and include **weight loss,** **lymphadenopathy**, **lameness** and **cutaneous signs**.  **Clinical and historical findings** **% of Dogs** -------------------------------------- --------------- Exercise intolerance 67.5 Weight loss 64 Lethargy 60 PU/PD 40 Anorexia 32.5 Diarrhoea 30 Vomiting 26 Epistaxis 6-15 Melaena 12.5 Sneezing 10 Coughing 6 Fainting 6 Most dogs develop **cutaneous signs** which may occur in the **absence of other systemic signs**. **Cutaneous signs** are very varied but include: **exfoliative dermatitis** with a **classic silvery scale** around the **muzzle** and **peri-orbital areas**, **peri-ocular alopecia** and **abnormal nail growth**. Due to **chronic immune system stimulation**, **polyclonal** **gammopathies** are often seen. **Proteinuria** **secondary** to **glomerulonephritis** is also commonly reported. Simon Tappin   7. **[Physical Examination:]** Clinical examination findings are also quite varied, however, **lymphadenopathy** and **cutaneous signs** are most frequently reported. Simon Tappin **Physical Examination Abnormalities** **% of Dogs** ---------------------------------------- --------------- Lymphadenomegaly 62-90 Skin lesions 81-89 Cachexia 10-48 Abnormal locomotion 37.5 Hyperthermia 4-36 Ocular disease 16-81 Splenomegaly 10-53 Onychogryphosis 20-31 Rhinitis 10 Pneumonia 2.5 Icterus 2.5 8. **[Knowledge Check:]** Which cells do progmastigotes invade in a mammalian host? Select all that apply. - **Macrophages ** - Lymphocytes - Monocytes - Erythrocytes - **Granulocytes** What are the peak age prevalences for Leishmania infection?  Select all that apply. - **\12 years old The most common abnormal finding on clinical examination is: - **Skin lesions** - Lameness - Lymphadenopathy - Ocular disease 9. **[Diagnosis:]** In a sick dog with overt signs of Leishmaniasis, diagnosis should be relatively straight forward. This can be done by documenting the **presence of the organisms** (through **cytology of lymph node**, **bone** **marrow** or **spleen samples**, or by **PCR** of **blood**, **bone marrow** or **tissue**), or by **detecting an immune** **response** to the **presence of the organism** (**serology**). Simon Tappin **Haematology** and **biochemistry changes** are **not specific** but reflect **chronic immune stimulation** and the **effects of immune-mediated disease**. **Laboratory Finding** **% of Dogs** ------------------------ --------------- Increased Globulins 71 Decreased albumin 68 Anaemia 58 Positive ANA 53 Neutrophilia 24 Thrombocytopenia 29 Positive Coombs test 21 Azotaemia 16 Elevated liver enzymes 16 For native British dogs that have travelled to endemic areas, Leishmaniasis should be considered in cases showing any potential clinical signs. Diagnosis in these cases can be made on the basis of clinical signs and confirmed by documenting the presence of Leishmania organisms. Simon Tappin **Cytological examination** of **fine needle aspirates** obtained from **enlarged lymph nodes** or **bone** **marrow**, is a very specific way to document Leishmania promastigotes Afbeelding met paars, violet, Lila Automatisch gegenereerde beschrijving **PCR** is also a very specific way of diagnosing infection, although the **sensitivity** **depends** on the **tissue** **submitted**. **PCR** is **most sensitive in acute infection** (**88%**) and **declines** with **chronicity** as organisms are **sequestered** **into** **tissue** (**50-70%**). Arrange the following tissue samples in order,  from the most sensitive (1) to the least sensitive (6) tissue sample for **PCR diagnosis** of leishmaniasis. Simon Tappin  1. **[Diagnostic Tree for Canine Leishmaniasis:]** Afbeelding met tekst, schermopname, Lettertype, lijn Automatisch gegenereerde beschrijving The diagnosis of chronic Leishmaniasis in dogs from endemic areas or those imported by rescue centres can be more challenging. The chronic insidious nature of the disease, coupled with vague clinical signs, is compounded by the fact that the presence of the organisms may not be the cause of the clinical signs seen. In these cases, looking for direct evidence of infection by **cytology** and/or **PCR** should be the starting point, but **negative results** **do not completely exclude** the **presence** of the **disease**. In these cases, **serology** is very helpful, **as high antibody titres suggest the disease is present**. Simon Tappin 10. **[Treatment:]** Treatment for Leishmaniasis is rarely curative, thus therapy is aimed at controlling the clinical signs rather than curing the disease. Treatment is protracted and is of variable success. Simon Tappin Allopurinol is the mainstay of treatment and is usually used in combination with meglumine antimoniate or miltefosine. Meglumine antimoniate is a pentavalent antimony compound that selectively **inhibits leishmanial glycolysis** and **fatty acid oxidation** and is used in both human and **veterinary medicine**. Miltefosine was developed as an anti-cancer drug and is now used to treat Leishmania. It is an alkylphosphocholine which **inhibits cell signalling** and **membrane synthesis** leading to **cell death**. Neither meglumine antimoniate (Glucantime) nor miltefosine (Miltefosine) is licenced for use in the UK, thus a Special Import Certificate is needed from the Veterinary Medicines Directorate. +-----------------------+-----------------------+-----------------------+ | **Drug Combination** | **Dose** | **Possible side | | | | effects** | +=======================+=======================+=======================+ | Meglumine | 75-100mg/kg SC every | Possible | | antimoniate  | 24 hours for 4 weeks | **nephrotoxicity**  | | | | | | & | 10mg/kg PO every 12 | **Pain** on | | | hours | **injection** | | Allopurinol  | | | | | | **Injection site | | | | reactions** | | | | | | | | **Xanthine | | | | urolithiasis** | +-----------------------+-----------------------+-----------------------+ | Miltefosine  | 2mg/kg PO every 24 | **Vomiting**  | | | hours for 4 weeks | | | & | | **Diarrhoea**  | | |   | | | Allopurinol  | |   | | | 10mg/kg PO every 12 | | | | hours | **Xanthine | | | | urolithiasis** | +-----------------------+-----------------------+-----------------------+  Recently, attention has been focused on treatment that may help encourage a **cell mediated Th1 immune response to infection**. Domperidone (Leisguard or generic in the UK) is a **dopamine receptor antagonist** which is usually used for its gastric prokinetic and antiemetic actions. Its **anti**-**dopaminergic effects** result in the release of serotonin, which in turn leads to the release of prolactin which is a proinflammatory cytokine thought to help modulate the **Th1 response**. A recent study using domperidone clinically found that it helped to **reduce clinical signs** and **antibody titres** in affected dogs, with no reported side effects (Gómez-Ochoa *et al.,*2009). Simon Tappin **Use of domperidone in the treatment of canine visceral leishmaniasis: A clinical trial ** Afbeelding met tekst, Lettertype, schermopname, lijn Automatisch gegenereerde beschrijving 11. **[Prevention:]** 2. **[Vaccination:]** Recently a **canine vaccination** against Leishmania has been brought to the UK market. This utilises cutting edge vaccine technology to combine a specific mixture of Leishmania surface proteins (known as excreted-secreted proteins or ESP) with a specific saponin adjuvant, to direct the **immune system** to a **Th1 cell mediated response** by the **induction of cytotoxic T-cells.** Simon Tappin Studies have shown that the **vaccine** is **extremely promising** and appears to greatly **reduce the risk** of **infection**. In a field trial performed between two sites, both in highly endemic areas, the vaccine was shown to reduce the risk of infection by **fourfold** in dogs housed outside without any other preventative treatment (CaniLeish technical product profile). It is thought that **vaccination** is likely to have a **greater protective effect in less endemic areas**. As with any vaccine, it is important to remind clients that the vaccination compliments rather than replaces other preventatives measures. The induction course is **3 injections at 3 weekly intervals**, with **annual boosters thereafter**. **Transient mild injection site reactions** have been reported with a **slightly higher frequency** than for **standard canine vaccinations**.  3. **[Parasite control:]** For naïve dogs traveling to endemic areas, reducing possible exposure to sand flies is essential in trying to prevent Leishmaniasis. Sand flies are **crepuscular**, meaning they are most active at **dawn** and **dusk**. Keeping animals **housed** during those times and using fine mesh screens to keep sand flies out of kennel areas will limit exposure. Deltamethrin-impregnated collars are also very effective at reducing bites from Phlebotomus flies. 4. **[Prognosis:]** A **cure** is **unlikely**, although clinical improvement is often seen unless severe organ disease is present. In this respect, the development of **renal failure** and **glomerulonephritis** is a **poor prognostic sign**.  12. **[Case Example -Frodo:]** This is Frodo, a 5 year old Greyhound who had been imported from Spain at the end of his racing career and had been in the UK for 18 months before he became unwell. He had gradually become listless, lethargic and lost weight, so was presented for further evaluation. Simon Tappin Afbeelding met Hondenras, huisdier, boord, snuit Automatisch gegenereerde beschrijving On examination he had markedly **crusting foot pads** with significant **hyperkeratosis**. He also had a generalised but **mild lymphadenopathy**.  Frodo was admitted and blood samples were taken. These revealed a marked **azotaemia** and a significant **hypoalbuminaemia** (12g/l). The low albumin was due to **a protein losing nephropathy** and his **UPC** **ratio** was **34**. **Serology** was positive for Leishmania and amastigotes could be seen in macrophages on cytology of the lymph nodes.  He commenced treatment with intravenous fluid therapy and allopurinol, but there was very little response and sadly he was euthanised as a result. Simon Tappin 13. **[Dirofilariasis:]** Adult *Dirofilaria immitis* reside in the **pulmonary arteries** and the **right ventricle** and usually lead to little **direct obstruction to the vasculature**. However, over time and with increasing worm burden there is **proliferation of vessel walls**, leading to **narrowing** and **obstructive signs** (pulmonary hypertension and pulmonary thrombosis). Adult worms produce microfilariae which are released into the bloodstream. More than 70 species of mosquito have been shown to be competent vectors for *D.immitis *with *Aedes caspius*, *Aedes geniculatus* and *Aedes punctor* reported in Europe. Image courtesy of Luca Ferasin 14. **[Worldwide Distribution:]** Currently,* D.immitis* is not endemic in the UK, however, it is widespread throughout most of North America and Southern Europe (see ESCCAP map below). Simon Tappin  Afbeelding met schets, diagram, tekening, kaart Automatisch gegenereerde beschrijving In the USA, the major foci of infection are along the Gulf coast, Eastern Seaboard and the Mississippi river valleys and tributaries, though any area of mainland USA except for the inland Northerly and Westerly states are affected. Incidence of disease caused by adult worms can be year-round. Dogs less than 6 months of age are not old enough to develop patent adult infections (i.e. show signs of disease), but are susceptible to infection and **prophylaxis** should start from **8 weeks of age**. Large male dogs housed outdoors are the most commonly affected group of dogs to be infected with heartworm. Simon Tappin In Europe the most common countries from which affected animals may originate are Spain, Portugal, south of France, Greece, Turkey and Eastern Europe, (especially Serbia and Croatia, although the species *Dirofilaria repens* is more common in these areas). The largest endemic area in Europe is along the Po river basin in northern Italy (near Turin, Milan, Piacenza, Ferrara). The most northerly, apparently autochthonous (i.e. occurring without the dog having travelled out of the area), case of heartworm in Europe has been reported in Cherbourg northern France, which is not too far from the southern coast of the UK.  Computer modelling studies using historical meteorological data, show that whilst it is currently not possible for more than one generation of Dirofilaria to become established in the UK, in the recent past climatic conditions have existed which would support Dirofilaria maturation. Such models in the USA have consistently shown to overestimate the risk of Dirofilaria geographic range and to overestimate also the length of the observed 'heartworm season'. Nonetheless, if global warming is a reality, then Dirofilaria may start to be seen on these shores. Simon Tappin 15. **[Lifecycle:]** Afbeelding met tekst, schermopname, Lettertype, nummer Automatisch gegenereerde beschrijving  Afbeelding met tekst, schermopname, Lettertype Automatisch gegenereerde beschrijvingAfbeelding met tekst, schermopname, Lettertype, nummer Automatisch gegenereerde beschrijving 5. **[Dirofilaria immitis:]**  1. Mosquito takes a blood meal (L1 larvae enter bite wound) 2. Adults in right ventricle of heart 3. Adults produce microfilariae that typically are found in peripheral blood 4. Mosquito take a blood meal (ingests microfilariae) 5. Microfilariae penetrate the mosquito's midgut and migrate to the malpighian tubules 6. L1 larvae 7. L3 larvae 8. Migrate to head and mosquito's proboscis Afbeelding met tekst, Lettertype, schermopname, lijn Automatisch gegenereerde beschrijving 6. **[Pathogenesis:]** The dog is the primary host for *D.immitis* and zoonotic infections are rare. **Zoonotic disease** in man is usually the result of a single nematode which **rarely** **reaches** **maturity**. As the worm dies a **thromboembolic** **event** ensues, evaluation of which can be misdiagnosed as a more severe malignant disease.  16. **[Knowledge Check:]** Heartworm contains an intracellular organism called Babesia. 1. True 2. **False** Infective L3 larvae are inoculated into the subcutaneous tissues of dogs when an infected mosquito feeds. 1. **True** 2. False Mosquitoes ingest L1 larvae when they take a blood meal. 1. True 2. **False** Adult worms reach sexual maturity at least 6 months after inoculation. 1. **True** 2. False Within the heart, the cranial pulmonary arteries are most commonly affected. 1. True 2. **False** Immature adults will test positive on antigen tests. 1. True 2. **False** 17. **[Clinical signs:]** Most infected dogs have few clinical signs, however signs can develop if **pulmonary arterial disease** is present. **Irritation** to the **pulmonary endothelium** **leads** to **pulmonary thromboembolism** and **hypertension**, which can cause coughing, dyspnoea, chronic weight loss, exercise intolerance and syncope. The severity of these signs depends on the **number** of worms present, the **duration** of **infection** and the **host immune response**. In severe cases, **haemoptysis** has been reported secondary to pulmonary arterial rupture. Simon Tappin Clinical examination findings are typical of dogs in **right sided congestive heart failure** (jugular distension, ascites, hepatomegaly), with a **systolic heart murmur** or **split** **S2**, with a **PMI** **over** **the** **right apex**.  Clinical signs vary with the **severity of disease**, but dogs have been subdivided by the American Heartworm Society into four classes based on clinical signs, physical examination findings and radiographic findings: ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- **Class** **Clinical Signs** **Physical Exam Findings** **Radiography** ------------------------- ----------------------------------------------------------------------------------------------------------- ------------------------------------------------------------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------------------- 1\ None to occasional cough Normal examination No lesions Mild 2\ Cough, moderate exercise intolerance Increased bronchovesicular sounds, fair body condition Slight pulmonary artery enlargement, mixed alveolar/interstitial lung  infiltrate Moderate 3\ Persistent cough, exercise intolerance, weight loss / cachexia, dyspnoea, overt right-sided heart failure Increased bronchovesicular sounds, accentuated or split S2, right apex gallop, tachypnoea / dyspnoea, jugular venous distension, ascites Moderate to severe pulmonary arterial enlargement, RV enlargement, severe pulmonary infiltrates Severe 4\ Acute collapse, anorexia, weakness, tachypnoea/dyspnoea Findings as listed  above and in addition pallor, haemolysis, haemoglobinuria Moderate to severe pulmonary arterial enlargement, RV enlargement, severe pulmonary infiltrates (severe caval syndrome) ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- 7. **[Caval Syndrome:]** **Caval syndrome** is an acute manifestation of a large worm burden causing obstruction to the **tricuspid valve apparatus** and results in: - **Acute decrease** **in forward blood** flow through the **pulmonary vasculature** to the **left side of** the **heart**, causing **left forward failure** and **acute signs** of **weakness**, **hypotension** and **shock** - **Right heart failure** -- **jugular venous distension**, **ascites** - **Haemolysis** due to shear stress on red cells - **Haemoglobinuria**, **acute renal failure**  18. **[Diagnosis:]** 8. **[Blood tests:]** **Routine haematology** may reveal **eosinophilia** and **basophilia** and **biochemistry** may reflect **secondary changes** to other organs (e.g. **mild increases** in **liver enzymes** and **pre-renal azotaemia**). C-reactive protein has been shown to increase in dogs with *D.immitis *and appears to correlate with the **severity** of the **pulmonary disease**. Simon Tappin The **most common** way to look for adult Dirofilaria is by using the **in-house SNAP test** (part of the D4X test that we have mentioned for other diseases such as Ehrlichia and Borrelia). This is an **antigen test** that looks for ciliary proteins from females. The higher the number of females present the **more sensitive** the **test** becomes.  Afbeelding met tekst, schermopname, nummer, diagram Automatisch gegenereerde beschrijving **Antibody tests** are **not often** **used** and are **less sensitive** and **specific** than **antigen tests**. **PCR** **tests** are **very sensitive** and **specific**, but at present they are not widely available. 9. **[Cytology:]** Microfilaria can be seen on blood smears; however, they are easier to find using the modified Knott's test. This is performed by taking **1ml of EDTA blood** and mixing it with **9ml of 2% formalin**. The tube is **inverted several times** **to** **lyse red cells** and then put through a **centrifuge** at **1000**-**1500rpm** for **5 minutes**. Any liquid is discarded and a drop of methylene blue is added to the sediment and a drop is placed onto a slide with a coverslip. Dirofilaria microfilariae will be 300-325 microns long and have tapered heads, which differentiates them from other vascular species such as Acanthocheilonema.  Image & video courtesy of Luca Ferasin 10. **[Radiographs:]** Afbeelding met röntgenfilm, Medische beeldbewerking, radiologie, röntgenfoto Automatisch gegenereerde beschrijving 1. Bronchoalveolar lung pattern, prominent caudal vena cava, enlarged right ventricle 2. **Interstitial lung pattern, prominent pulmonary artery, enlarged right ventricle** 3. Interstitial lung pattern, prominent descending aorta, normal sized right ventricle 4. Bronchoalveolar lung pattern, prominent caudal vena cava, normal sized right ventricle Thoracic radiographs may be normal, but in advanced cases they show signs associated with **right sided** **cardiac disease** and **pulmonary hypertension** due to the presence of adult worms. This manifests as a **pulmonary arterial bulge**, with **enlarged** and **tortuous pulmonary arteries**.  The dorsoventral view here shows a **prominent main pulmonary artery** (**MPA**) that becomes **tortuous** and **pruned** as the **pulmonary arteries** (**PA**) get further out into the **periphery**. **Right-sided ventricular hypertrophy** (**RVH**) is also apparent. Simon Tappin 11. **[Echocardiography:]** **Cardiac changes** are confirmed on **echocardiography** and usually, reveal **right ventricular hypertrophy** and **pulmonary hypertension** (which is documented by measurement of the velocity of any regurgitant jet from the **tricuspid valve**). Adult worms may be visualised at this point in the main **pulmonary artery** and less often in the **right-side chambers** of the **heart** as seen in the images below.  The worms are the white lines in the pulmonary artery, highlighted by the arrows. 19. **[Treatment:]** 12. **[Medical:]** **Several treatment** **options** are available and in low worm burdens this includes conservative management. Steroids at anti-inflammatory doses may help to reduce **pulmonary inflammation** and the risk of **thromboembolism** before more definitive therapy is given. **Signs** of **congestive heart** **failure** may be controlled with **thoracocentesis** and **diuretics** as required. Simon Tappin Aspirin or clopidogrel should also be considered to **reduce the risk** of **thromboembolic disease**. Killing adult worms is not without risk as these will be swept into the pulmonary tree leading to **thromboembolic events**. If attempted, this is usually under experienced specialist supervision using the drug melarsomine. This is usually given as a **single injection** (which kills 90% of male worms and 10% of female worms), followed by a **pair of injections 24 hours apart after 50 days**. This 3 injection approach **reduces** the **worm burden gradually**, **reducing the potential risk** of **thromboembolism**. Another option that has been trialled is the use of long term microfilaricidal drugs, or what are known as 'slow kill' drugs. Whilst there does seem to be some evidence that this approach helps improve the quality of life in clinical cases, the American Heartworm Society does not recommend this approach. The reason for this is that whilst effective in reducing the life span of juvenile heartworms, the data suggests that the older worms are less susceptible, taking longer to die. Simon Tappin It has been shown that it takes more than **2 years** before adult heartworms are **95% eliminated** when continuously treating a patient with macrocyclic lactones. Throughout this period, the infection would persist and pathology would continue to progress. There is also a concern that if macrocyclic lactones are used as a monotherapy in heartworm-positive dogs, there is the potential for selection of resistant subpopulations of heartworms. 13. **[Surgical:]** An alternative treatment is **surgical removal** via a **vascular approach**. This approach is suggested if worms are present in the **right side of the heart** and there are **signs** of **caval syndrome**. This is usually achieved using **Ishihara forceps** through a **right sided jugular approach** and requires a good deal of skill as well as **fluoroscopic** and **ultrasound guidance** to be successful. Simon Tappin  20. **[Prevention:]** Preventing infection by chemoprophylaxis with monthly milbemycin or selamectin has proven efficacy (both are also safe in collie breeds with MDR-1 abnormalities). If animals are travelling, their heartworm prophylaxis should be continued for at least **1 month after returning to the UK.** Further information can be found in the American Heartworm Society guidelines: Simon Tappin **American Heartworm Society guidelines** [**[CLICK HERE](OPENS IN A NEW TAB)**](https://d3ft8sckhnqim2.cloudfront.net/images/pdf/2019_AHS_Canine_Guidelines.pdf?1593655116) ------------------------------------------------------------- **Compound** **Presentation** **Dog (min-max dosage)** -------------- ------------------- -------------------------- Ivermectin Tablets/chewables 6-12 µg/kg Milbemycin Flavour tablets 0.5-1 mg/kg Moxidectin Tablets\ 3-6 µg/kg\ Injectables\ 0.17 mg/kg\ Topical 2.5-6.25 mg/kg Selamectin Topical 6-12 mg/kg ------------------------------------------------------------- 14. **[Wolbachia:]** Wolbachia organisms play a role in the pathogenesis of **canine and feline heart disease**. Wolbachia is a gram-negative bacterium of the rickettsial order. It is an endosymbiont of *D.immitis* and **antibodies** to Wolbachia are commonly found in affected animals, although its exact role is currently unclear (Kramer et al., 2008). Treatment of Wolbachia with doxycycline (10mg/kg BID for 4 weeks) has been shown to improve clinical outcomes in dogs if given prior to the administration of melarsomine. 15. **[Subcutaneous Dirofilariasis:]** Subcutaneous Dirofilariasis is mainly caused by *D.repens *and infects domestic dogs in Europe (mainly Italy, Spain, Greece and the south of France), as well as Asia and Africa. It is transmitted by a different mosquito species to *D.immitis *transmission, but has a very similar life cycle, with the worm living in the subcutaneous tissues.  16. **[Dirofilaria Repens:]**  1. Mosquito takes a blood meal (L3 larvae enter bite wound) 2. Adults in subcutaneous tissue 3. Adults produce microfilariae that typically are found in peripheral blood 4. Mosquito takes a blood meal (ingests microfilariae) 5. Microfilariae penetrate mosquito's midgut and migrate to malpighian tubules 6. L1 larvae 7. L3 larvae 8. Migrate to head and mosquito's proboscis The **clinical significance** of the **worms** is not clearly defined and most infections are asymptomatic. The **worms mature** over **6-7 months** and the females grow up to **25-30cm in length** (the males are shorter) and are **1-2mm in diameter**. **Subcutaneous nodules** are normally removed surgically (see YouTube video below) and macrolide preventatives used for *D.immitis *are usually successful in preventing disease transmission. Simon Tappin 21. **[Completion of Online Learning:]** You have now completed Week Three, Lesson One of Canine Infectious Diseases. Simon Tappin **To recap the learning objectives, you should now be able to:** 1. Review the aetiology and pathophysiology of Leishmania and Dirofilaria; 2. Recall the clinical signs associated with Leishmania and Dirofilaria; 3. Outline how to make a diagnosis of Leishmania and Dirofilaria; 4. Consider the treatments options for dogs with Leishmania and Dirofilaria; 5. Reflect on preventative strategies.