Pathology for VetsPathology for VetsThe 2009 Combo ChallengeThe 2009 Combo Challenge

Dr Rick Last

Specialist Veterinary PathologistCPD Accredited Activity

Dilated cardiomyopathy of dogsDilated cardiomyopathy of dogsKey Gross Pathological FindingsKey Gross Pathological Findings

Biventricular dilatation

Two apexes (arrows)

Heart has rounded shape

Ventricular lumen dilatation

Ventricular wall thinning

Distension of AV valve (arrows)

Dilated Cardiomyopathy of DogsDilated Cardiomyopathy of DogsHistopath Diagnostic ClinchersHistopath Diagnostic Clinchers

Fatty infiltration degenerative type

Myofibre atrophy and dissaray

Interstitial fat deposits and fibrosis

Diffuse subendocardial fibrosis

Attenuated wavy type Myofibres thin and attenuated (L ventricle) Arranged in a loose wavy pattern Diffuse subendocardial fibrosis

Two Histopathological Forms = different disease process

Dilated Cardiomyopathy of DogsDilated Cardiomyopathy of DogsFact FileFact File

Dilated cardiomyopathy (DCM) has been recognized in many breeds butseems more prevalent in certain breeds, a recent survey of 76 dogs with DCMindicated this condition to be most common in Great Danes (46%) followedby St.Bernhard (10%), Newfoundland (10%), Neapolatan mastiff (5%),Rottweiler (3%), Dougue de Bourdeux (3%), Boxer, Labrador, Leonberger,Collie, Dalmation, English Cocker Spaniel, GSD, Greyhound, IrishWolfhound and mongrel (2% each). The exact aetiology of individual casesusually remains undetermined however, several factors have been proposedincluding genetic factors, nutritional deficiencies, metabolic disorders,immunological abnormalities, infectious diseases and drug toxicities.

In dogs familial DCM has been shown in a number of breeds; (Irishwolfhounds, boxers, dobermans, Newfoundlands, weimaraners) an autosomaldominant mode of inheritance is suspected, while in the Portugese Water Dogautosomal recessive transmission has been documented. It is likely thatdifferent breeds have different gene defects. A defect in the cytoskeletal genedystrophin has been identified as a cause of X-linked DCM in Germanshorthaired pointers which also have concurrent skeletal myopathy.

Nutritional myopathies causing myocardial hypokinesis (decreased motoractivity) i.e. carnatine and taurine deficiencies have been documented in dogs,cats and humans. Metabollic disorders which have been associated withDCM include hypothyroidism, diabetes mellitus and phaeochromocytoma.Cardiotoxin agents which induce tachycardia with chamber dilatation andCHF include doxirubicin and other antineoplastic agents, ethanol, cobalt, lead,catecholamines, histamine, methylxanthines and vitamin D.

Mycotic Abortion in the BovineMycotic Abortion in the BovineKey Gross Pathological FindingsKey Gross Pathological Findings

Cotyledons enlarged brown withroughened leathery necrotic surface

Extension of lesions fromcotyledons to intercotyledonaryarea (arrow), consistent withhematogenous spread

Fetal mycotic dermatitis frequentlyaccompanies mycotic placentitis

Lesions are raised white plaques

Distribution of fetal skin lesions areperi-orbital, shoulders, backs andflank

Mycotic Abortion in the BovineMycotic Abortion in the BovineHistopath Diagnostic ClinchersHistopath Diagnostic Clinchers

Aspergillus fumigatus characterized in section by septate, uniform fungalhyphae (image on left) accounts for 75% of cases

Zygomycetes (Absida, Mucor, Rhizopus, Mortierella) non-septate, variablethichness hyphae in section (image on right) account for 25%

Pseudallescheria boydii and yeasts (Candida, Torulopis) are considered rarecauses of mycotic abortion in cattle

Invasion of blood vessels by fungal elements (asterix) = consistent finding

Mycotic Abortion in the BovineMycotic Abortion in the BovineFact FileFact File

Mycotic Rumenitis

Mycotic abortions in cattle tend to occur between 6-8 months gestationand placenta’s are usually firmly retained. Gross lesions are usuallyconfined to the placenta and fetus. Endometrial lesions are usually lesssevere than placental lesions but secondary infections may followretention of the placenta. In ruminants it is thought that fungi originatefrom the maternal respiratory tract or from ruminal lesions and spreadhematogenously to the placentomes with further spread to theintercotyledonary areas of the placenta.

Mycotic abortion accounts for 6-7% of bovine abortions. Asendometrial lesions, in general, are less severe than in the placenta, longterm fertility of these animals is not affected and the majority of cowsrecover after abortion and calve again. However, in cases of severeendometrial destruction breeding future of the cow maybe adverselyaffected.

Fetal cutaneous lesions have a site predeliction for periorbital areas,shoulders, back and flanks. Occasionally the fetus may aspirateorganisms from the amniotic fluid initiating a bronchopneumonia, buttypically there is no systemic spread from the skin sites. Swallowing ofamniotic fluid by the fetus on the other hand is a common occurrenceand hence fungal culture from the abomasal fluid of the fetus is a usefuland effective diagnostic tool.

Greasy Pig DiseaseGreasy Pig DiseaseKey gross featureKey gross featureAcute, often fatal bacterial dermatitis with a peakincidence between 5 and 35 days of age. The causativeorganism is Staphylococcus hyicus which produces anexotoxin “exfoliatin”,. There is direct proteolysis ofswine desmoglein-1 (Dsg-1), a calcium-dependant cell tocell adhesion molecule in desmosomes, by S.hyicusexfoliative toxin. Resulting in the pustular crustinglesions.

Predisposing factors include cutaneous lacerations, poornutrition and viral infections. Dermatitis with abrownish exudate usually develops around the eyes,pinnae, snout, chin, medial legs and spreads to theventral thorax , abdomen and coronary bands.

Aortic spirocercosis in dogsAortic spirocercosis in dogsIngested L3S.lupi larvae penetrate the gastric mucosa of thefinal host, from where they migrate subintimally, in theadventitia and media of the walls of arteries, reaching thecranial aorta within about 3 weeks. Here they may remain asaortic granulomas for 2 - 4 months, before moving to theirfinal destination in the oesophagus, reaching adulthood.

Heavy aortic larval loads can cause severe transmural aorticinflammation with numerous necrotic tracts and proliferativeendarteritis. Such aortas are prone to rupture with fatalhemothorax and this frequently occurs in the absence ofoesophageal granulomas. The rise in systemic vascularpressure (blood pressure) following tranqulization can putincreased shear stresses on an already compromised aorta,making these dogs an anaesthetic risk.

Canine severe eosinophlicCanine severe eosinophlicdermatitisdermatitisCanine severe eosinophilic dermatitis characterized byacute eosinophilic dermatitis with vasculopathy /vasculitis and oedemaand has been described as a discretesyndrome in dogs. Recent retrospective studies haveshown that many cases have followed treatment of severegastrointestinal illness and it is proposed that the skincondition may have a causal drug association, possiblydrug combination effects or perhaps due to a moregeneralized hypersensitivity response. Skin lesionsusually develop within 7 days or sooner followinginstitution of treatment with multiple drugs for GI disease.Cutaneous lesions are characterized by erythematous tohemorrhagic macule or plaques through to ulceratednodules, distribution being predominantly on the ventralabdomen , flanks and limbs.

Rhodococcus equiRhodococcus equipneumonia in foalspneumonia in foalsRhodococcus equi is an important bacterial pathogen of horsesbeing associated with pyogranulomatous bronchopneumonia offoals, with about 50% of these foals developing concurrentulcerative colitis and in some foals intestinal lesions occuralone. It is less commonly associated with clinical disease inother animal species (cats, cattle, sheep, goats, pigs and llamas)and is emerging as an important pathogen inimmunocompromised humans (HIV, hematopeiticmalignancies, chemotherapy patients, transplant recipients).

In addition to being a common soil inhabitant R.equi isfrequently part of the alimentary flora of mammals and birds.There are both virulent and avirulent forms of the bacteriumwith about 88% of isolates from foals being the highly virulentvariant (VapA). Nearly all isolates from pigs are theintermediate virulent VapB strains, while many humans developclinical disease with the avirulent strains, due toimmunosuppression.

Pathogenesis of foal pneumonia is related to aerosol infectionwith bacteria being taken up by macrophages. Theseintracellular bacteria survive within macrophages by interferingwith phagosome-lysosome fusion and inhibiting oxidativebacteriocidal functions of neutrophils. The primarymanifestation of disease is pyogranulomatousbronchopneumonia and abcessation in the absence of pleuritis.Repeated swallowing of respiratory exudate by foals is probablyan important source of infection for the development ofconcurrent intestinal lesions.

Feline InfectiousFeline InfectiousPeritonitisPeritonitis

Infection is usually oral although respiratory andtransplacental transmission have been described.Outcome of coronavirus infection depends largelyon the particular strain of virus involved and theability of the cat to mount a strong cell mediatedimmune response. Following inf ectionmacrophage / monocyte associated viraemia thendevelops with dissemination of the virus aroundthe body. These activated monocytes and thecytokines they produce are central in thedevelopment of the multisystemic vasculitis(phlebitis) and pyogranulomatous inflammationtypical of this disease.

Central nervous system pathology ischaracterised by a fibrinous andpyogranulomatous periventriculitis with theexudate sometimes resulting in the occlusion ofthe mesencephalic aqueduct between the third andfourth ventricles (arrows), resulting in internalhydrocephalus. Other CNS lesions which havebeen documented include meningitis,leucoencephalitis, segmental myelitis andchoroiditis.

Lymphoid leukaemia in aLymphoid leukaemia in aGaboon adderGaboon adder

Acute lymphocytic leukaemia, myelogenousleukaemia, lymphocytic leukaemia withmulticentric T-cell lymphoma, lymphoma withlymphoid leukaemia and myeloproliferativedisease, have all been described in snakes. Therehas been an association with retroviruses (TypeC) in some instances. Special cyto-chemicalstains on bone marrow and organ smears pluselectron microscopy are often required fordefinitive diagnosis. In this example there ismarked hepatomegaly due to extensiveneoplastic infiltrates in portal vessels andsinusoids. The histological images are of themyocardium with interstitial vessels engorgedwith neoplastic lymphocytes.

Ionophore poisoning in cattleIonophore poisoning in cattle

Most outbreaks involve mixing errors in commercialand home-mixed concentrate rations, althoughmaduramycin poisoning has been documented withthe feeding of chicken litter to cattle and sheep.

In cattle pathology is characterized by cardiac andskeletal muscle damage of equal severity, skeletalmuscle pathology with myoglobinuria predominatesin sheep and swine, while in horses myocardialdamage predominates. Hindlimb muscles may be thesite of severe degenerative changes. Grossly thesedegenerative changes are characterized by whitestreaking and pale foci in skeletal and cardiac musclewith haemorrhage. Terminal cardiac cases revealmyocardial necrosis (arrow + note streaking ofdiaphragm), fluid accumulation in body cavities(stars), pulmonary congestion and oedema andhepatic congestion. Histopathology is characterizedby multifocal degeneration and necrosis with lesionsof similar duration (monophasic)

Ionophore toxicity in cattle may be potentiated byconcurrent vitamin E selenium deficiency, clinical orsubclinical acidosis, gossypol contamination (onwhole cotton seed), exposure to other cardiotoxicplants or concurrent use of certain antibiotics(doxycycline, tiamulin, erythromycin,chloramphenicol, tylosin, tilmicosin)

Heart base tumoursHeart base tumoursin dogsin dogs

Extra-adrenal paragangliomas are adiverse group of neuroendocrinetumours that may arise from multiplesites in the body. The paraganglia aremade up of the adrenal medulla,chemoreceptors, vagal body and smallgroups of cells associated with thethoracic, intra-abdominal andretroperitoneal ganglia. They areclassified into 3 groupsphaeochromocytoma, extra-adrenalparagangliomas and chemodectomas.The most common heart base tumoursare hemangiosarcoma of the rightatrium, chemodectomas, ectopicthyroid tumours and ectopicparathyroid tumours. Chemodectomasare rarely invasive and slow tometastasize and thereforepericardiectomy is an option in thesecases. Neoplasms of chemoreceptororigin occur primarily in dogs withinfrequent occurence in cats and cattle.

Note in this case how thechemodectoma has entirelyencompassed but not invaded the aorta.

Renal gout in reptilesRenal gout in reptiles

In reptiles uric acid is the main end product ofprotein metabolism and in most reptiles’ uric acid isthe main component of the urine . It is primarilyexcreted by the proximal convoluted tubules withminimal excretion by glomeruli. Risk factors forthe development of gout in reptiles includehyperuricaemia caused by renal dysfunction(particularly tubular disease), dehydration and /orintake of purine rich diets. This latter conditionbeing common in herbivorous animals fed a diethigh in animal protein. (Gross image of leguaankidney showing chalky white urate accumulates).

In early renal gout deposition of uric acid crystals isin proximal tubular epithelial cells (usually seen ascrystal ghosts in histological sections). Thesecrystals act as the nidus / crystallization centers forfurther deposition, breaking through the tubularepithelial basement membrane initiating aninflammatory response resulting in the characteristicurate tophus formation. Urate tophi consist ofcentral radially arranged urate crystals surroundedby macrophages, giant cells and variable numbersof heterophils and lymphocytes. Tophi maybefound throughout the kidney often occludingtubules, in the interstitium and rarely mesangium ofglomeruli. (See histopathology image right)

Vitamin E selenium deficiencyVitamin E selenium deficiencyAborted bovine fetusAborted bovine fetusVitamin E selenium deficiency is known to affect allphases of the reproductive cycle including

Failure to conceive

Embryonic death

Abortion (fetal tissues with low selenium)

Stillbith and birth of weak calves

Retained placenta

The primary pathology in fetuses aborted due to vitaminE selenium deficiency is myocardial with accompanyingacute congestive heart failure. Most abortions are latestage with gross abnormalities characterized by visibleabdominal distension due to ascites (image top right),cardiac dilation with degeneration and/necrosis andhydropericardium, pulmonary oedema (prominentinterlobular septae), skeletal muscle degenerationand/necrosis and cardiogenic hepatic congestion (imagebottom right).

Selenium has the ability to cross the placenta in bothcattle and sheep to be sequestered in the fetal liver, evenwith low availability in the dam. Therefore, normalselenium reference ranges are significantly higher in thefetus compared to the adult (up to double the adultrange). The fetal kidney has been found to be the mostreliable organ for selenium analysis in an abortioninvestigation.

Vitamin E selenium deficiencyVitamin E selenium deficiencyBovine calvesBovine calvesIn suckling calves and weaned calves pathology is moreoutspoken in skeletal muscles used in physical activities.Suckling animals = tongue and neck muscles. In older calves= skeletal muscles and / or cardiac muscle. Extensive cardiacinvolvement (usually left ventricular) is frequentlyaccompanied by lesions in intercostal muscles and diaphragm(see gross images right) but other skeletal muscles are notaffected to the same degree. Histological lesions aremultifocal with lesions of various duration evident(polyphasic myopathy). Early changes are ofhypercontraction band formation with hyaline degenerationfollowed by necrosis and myofibre cytolysis. Mineralizationof necrotic fibres is common in calves (histo image below).Influx of inflammatory cells (macrophages and mononuclearcells) to clean up necrotic debris and replacement fibrosisfollows.

Equine PiroplasmosisEquine PiroplasmosisFetal InfectionFetal Infection

Equine piroplasmosis results from infection with eitherTheileria equi or Babesia caballi. There have beenvery rare instances of Babesia bovis infectiondocumented in horses. Infection has been reported inhorses, mules, donkeys and zebra with zebras acting asan important reservoir of infection in Africa. This is atick transmitted disease with over 14 species of ticks inthe genera Rhipicephalus, Hyalomma andDermacentor acting as vectors.

Infection of pregnant mares with Theileria equi at anystage in pregnancy is quite common. The consequenceof infection depends on the stage of infection butincludes reproduction failure (involved in up to 11% ofall failures in South Africa), abortion, neonatalpiroplasmosis and birth of asymptomatic carriers.Infection with Theileria equi can be persistent withdevelopment of carrier mares which can producefurther infected fetuses, randomly in subsequentpregnancies. Aborted fetuses usually demonstrateanaemia, moderate to marked icterus, petechiae onvisceral and serosal surfaces, hydrothorax,splenomegaly and hepatomegaly. (Image top right)Kidney reveals moderate nephrosis with icteric change.(bottom right) Parasitaemia is usually high.

Theileria equiTheileria equiBlood smear examinationBlood smear examination

Parasites are small with single, pairs and clusters of 4merozoites being the norm. (see images on right)

Theileria equi are fairly readily found in horses withacute infection, but are usually extremely difficult tofind in carriers.

Merozoites often connected in a tetrad “maltese cross”(see image below)

Feline hepatic lipidosisFeline hepatic lipidosis

Gross pathology: hepatomegaly with yellow-browndiscolouration, rounded borders and increasedfriability.

Histopathology: microvesicular and macrovesicularvacuolar change which alters contour of hepatocytesand displaces the nucleus. Minimal inflammation.

Hematological abnormalities

- poikilocytosis (abnormally shaped erythrocytes) inblood smears common due to abnormal erythrocytelipid membrane metabolism.

- abnormal clotting profiles observed in up to 50% ofcats with HL. Prolongation of prothrombin time dueto vitamin K deficiency most common.

- Hypofibrinogenemia is common.

Clinical chemistry abnormalities

- hyperbilirubinaemia with > 2x increase in AST, ALPand ALT with normal or mildly raised GGT

- Marked GGT increase, search secondary conditions

- Hyperkalaemia present in 30% of cases = negativeprognostic indicator

- Low urea and normal creatinine in 50% of cases dueto decreased urea formation

- Hypercholesterolaemia uncommon but if presentsearch for underlying pancreatitis or bile ductobstruction.

Rift Valley FeverRift Valley FeverBovine calvesBovine calvesNatural infection with RVF virus primarily occurs in livestock(small ruminants, cattle) and humans with rare clinical casesreported in camels, African buffalos and horses. Experimentalinfection has been recorded in mice, rats, hamsters, dogs, catsand macaques. Gross pathology in calves is characterized by;Diffuse hepatic necrosis with cholestasis (yellow discoloration)and capsular plus parenchymal haemorrhages. (Image topright).

Gastrointestinal haemorrhage with large suggillations in theabomasal serosa. (Image bottom right)

Nephrosis (image below) and splenomegaly.

Viral antigen is abundant in the RE system of multiple organs(liver, kidney, adrenals, GIT, brain, ovaries, endometrium) withvirus persisting at these sites for many weeks, making themuseful diagnostic samples for RT-PCR, virus isolation andantigen ELISA. Viraemia (virus in blood) lasts only2-5 days.

RVF histopathologyRVF histopathologyBovine calvesBovine calves-Multifocal random hepatic necrosis coalescing in someareas to form zones of pan-necrosis (Image top right)

- Fibrin deposition in sinusoids with haemorrhage and lytichepatocellular necrosis. Vasculitis is a well documentedand common lesion in calves which is not commonlydocumented in adults or fetuses. Widespread fibrinocellularthrombosis in portal vein and hepatic sinusoids (Imagebottom right).

- Hepatocyte nuclear chromatin margination with multiple,pale, eosinophilic, intra-nuclear inclusion bodies – arrows(Image below)

RVF histopathologyRVF histopathologyAdult bovineAdult bovine

-- Centrizonal pattern of hepatic necrosis (Image top right).

- - Scattered necrotic hepatocyte's, some with intracytoplasmiceosinophilic apoptotic bodies (arrow) distributed betweendegenerative hepatocyte's (Image bottom right)

- - Rare intranuclear inclusion bodies (arrows) and eosinophiliccytoplasmic apoptotic bodies (asterixis) (See image below)