Protozoa, Fungi, Helminths`

Brief description of pathogenesis of pathogenic Coccidia (protozoa)

Damage to enterocytes following rupture of mature schizonts and merozoite release

Villus atrophy = malabsorption

Epithelial erosions and ulceration = exudative enteritis

Impaired intestinal barrier and permeability = diarrhoea

Name the causative agent

Eimeria tenella

What is this?

Sarcocystis in skeletal muscle

Describe the pathogenicity of Sarcocystidae

Usually benign outside of the GIT

Forms cysts in muscle (including heart) but no inflammation

Disease occurs when

• cysts rupture

• dead/end host or nervous system infected (e.g. S. neurona in horses infects the spinal cord)

Causative agent

Trypanosoma spp.

What are the 2 major and 4 morphological forms of Trypanosoma and brief description

American (T.cruzi) and African (T. congolenese, vivax and brucei brucei)

Amastigotes (intracellular, T.cruzi only)

• no flagellum

• multiplies in mammalian cells

Trypomastigotes (blood form)

• infective

• does not multiply

Epimastigotes (intermediate form)

• found in vector (fly), multiplies in midgut

Promastigotes

• rapidly dividing stage

How do Trypanosoma evade immune system

Have antigenic variation in membrane surface glycoproteins

= host needs to constantly redevelop humoral immune response

= very hard to develop vaccine against it

What does chronic infection of T.cruzi cause

myocarditis

What does T. evansi cause in horses

meningoencephalitis = neurological signs

2 virulence factors of fungi

Capsule (yeast)

• polysaccharide. impossible to effectively phagocytose

• may contain melanin - antioxidant that inhibits lysosomal digestion

Constantly shedding surface antigens

= chronic inflammatory reaction = granulomatous inflammation

What is the causative agent?

Aspergillosis

3 virulence factors of aspergillosis

Gliotoxin = anti-inflammatory, apoptosis of phagocytes

Fumagillin and hevolic acid = antibiotics

Melanin = antioxidant

Pathophysiology of aspergillosis

Inhalation of conidia

Immunosuppression/disruption of phagocytosis = germination into hyphae. Secretion of enzymes that damage the epithelium, exposing the basal lamina and allowing easy colonisation and invasion.

Systemic spread via leukocyte trafficking, or rarely by angioinvasion

Gross appearance of aspergilosis in dogs

grey/black pseudomembraneous rhinitis/airways

Aspergillosis causes gross lesions on what organs of the cow

Lungs

Placenta

Udder

Gross appearance of fungal infections (2)

Fungal plaques (grey/red)

Haemorrhage (vasculogenic/brain, epistaxis)

4 examples of clinical signs caused by nematodes

Weight loss

Hypoalbuminaemia (PLE-causing)

Anaemia (Haemonchus contortus)

Diarrhoea

2 example nematodes that undergo hypobiosis and mass re-emergence

Cyathostomins (horse)

Ostertagia (cattle)

3 examples of nematodes that can cause death due to blood vessel damage

Strongylus vulgaris (horse = mesenteric vessels)

Angiostrongylus vasorum (dog = lungworm)

Haemonchus contortus (sheep = abomasal blood feeding)

Causative agent in a sheep

GID - tapeworm cyst from Taenia multiceps (infects dog GIT)

Causative agent

Trematode - liver fluke