Agents Terms + Definitions

Nematodes

Roundworms

Cestodes

Segmented Flatworms (Tapeworms)

Trematodes

Non-segmented Flatworms (ie. flukes)

Infectious Dose

The minimum amount of a pathogen (bacteria, virus, or parasite) required to cause an infection or disease in a host.

Parvoviridae

A family of small, ssDNA viruses, non-enveloped. Generally host-specific. Only replicate in the nucleus of dividing cells.

Parvoviridae Examples

Porcine Parvo —> SMEDI, oronasal

Canine Parvo —> CPV2, contagious enteric disease

Feline Panleukopenia Virus (FPV) —> enteric + systemic disease common in weaned kittens

Enteric Disease

Infections of the intestinal tract. Usually faecal-oral.

Systemic Disease

Disease that affects a number of organs and tissues, or affects the body as a whole.

Pappilomaviridae

A family of dsDNA, non-enveloped virsues. Very environmentally stable and host specific. WARTS! Epitheliotrophic.

Papillomaviridae Examples

Equine Sarcoids —> Bovine Papillomaviruses 1/2 into horses.

BPV

Canine Oral Papillomaviruses —> oral warts in young dogs

Poxviridae

Very large family of dsDNA linear, enveloped viruses. Replicate in cytoplasm, epitheliotrophic, carry their own transcription enzymes and can survive in scabs for years. Causes scabs, generally enter through skin abrasions, can cause systemic disease.

Poxviridae Examples

Orf Virus / Scabby Mouth —> Pustular lesions in sheep and goats, highly contagious, direct contact and environmental contamination, no viraemia —> death usually occurs from starvation.

Myxoma Virus —> used for biological rabbit control, causes viraemia

Herpesviridae

Family of large, dsDNA, enveloped viruses. Replicate in the nucleus, host-specific and have LATENCY. Have their own replication machinery.

Herpesviridae Examples

EHV-1 —> more severe, systemic + causes abortion, respiratory disease, neonatal infection + neurological disease

EHV-4 —> respiratory disease, often 4 months - 2 years

Feline Herpesvirus —> Feline Viral Rhinotracheitis

Picornaviridae

Family of positive sense, ssRNA viruses. Stable in environment and replication occurs in cytoplasm. Localised infection followed by viraemia and tend to be very contagious.

Picornaviridae Examples

Foot and Mouth Disease Virus (FMDV) —> apthovirus, highly contagious and causes fever + formation of vesicles/blisters on epithelial surfaces (mouth + feet), NOTIFIABLE

Caliciviridae

Family of positive sense, ssRNA, non-enveloped viruses. Wide range of tissue tropism, rapid cytoplasmic replication and cause cell lysis.

Caliciviridae Examples

Rabbit Haemorrhagic Disease Virus (RHDV) —> highly contagious + fatal disease of rabbits, mainly faecel-oral route, often peracute death due to liver failure (causes protein shutdown)

Feline Calicivirus —> a highly contagious virus that causes a mild to severe respiratory infection and oral disease in cats

Coronaviridae

A family of positive sense, ssRNA, enveloped viruses. Pleomorphic, contagious, replicate in cytoplasm, faecal-oral and cause enteric disease.

Coronaviridae Examples

Feline Coronavirus (FCoV) —> mutated form causes fatal systemic disease (Feline Infectious Peritonitis Virus (FIPV))

• spread from FCoV (NON MUTANT) shed in faeces → kitten exposed

  • replicate in enterocytes

  • the virus GETS INTO BLOOD STREAM

    • viraemia within macrophages

  • recombination or mutational change → FIPV

  • mutated version is not shed

Flaviviridae

Family of positive sense, ssRNA, enveloped viruses that replicate in cytoplasm. Mainly vector-transmitted and released by exocytosis (flavivirus = arboviruses, pestivirus = no insect vector).

Flaviviridae Examples

FLAVIVIRUS

West Nile Virus —> exotic to Australia, mosquito transmitted disease causing encephalitis in humans + horses, natural reservoir = birds

Kunjin Virus

Japanese Encephalitis Virus —> mosquito borne viral disease of humans + animals that occurs throughout Asia

• abortion in pigs

• encephalitis in humans + horses

• WAS exotic to Australia

• increases around warm, wet weather (Summer/Autumn) → mossie conditions

• mosquito-pig-mosquito transmission cycle → viral amplification

PESTIVIRUS

BOVINE VIRAL DIARRHOEA VIRUS (BVDV) —> one virus causing two different syndromes:

• bovine viral diarrhoea = acute disease

• mucosal disease = chronic disease

• oral-nasal route of transmission

Togaviridae

A family of positive sense, ssRNA, enveloped viruses that replicate in cytoplasm. Majority arboviruses. Cause encephalitis.

Togaviridae Examples

Eastern + Western Encephalitis Virus —> reservoir host = birds + small mammals (can cause mortality + disease in these), vectors = mosquitos + dead-end host = humans + horses (severe disease → EEE 90% fatality horses) BIPHASIC FEVER

Ross River Virus —> a mosquito-borne virus native to Australia and is the most common mosquito-borne disease in Australia, causing symptoms that typically manifest as severe joint and muscle pain, fatigue, and fever

Reoviridae

A family of positive sense, dsDNA, non-enveloped viruses with a segmented genomes. Replicate in cytoplasm, virions released by cell lysis.

Reoviridae Examples

Bluetongue Virus (Orbivirus) —> spread by biting midges and causes fever, ulcers and blue swelling of tongue in sheep. Replication in regional LN + carried in blood/lymph to lymphoid tissue for further replication → localisation + multiples in endothelium of small blood vessels.

Rotaviruses —> very important cause of enteritis + diarrhoea in intensively reared animals of ALL DOMESTIC SPECIES (considered to be species specific)

Orthomyxoviridae

Family of negative-sense, ssRNA viruses, enveloped and very prone to mutations. Have a segmented genome with two major glycoproteins (H and N, determine strain type).

Orthomyxoviridae Examples

Avian Influenza —> a highly contagious viral infection caused by influenza A viruses that primarily affect wild and domestic birds

• most human influenza pandemics are due to avian influenza + human influenza reassortment

  • PIG is the MIXING VECTOR → respiratory tract epithelium have receptors for both avian + human influenza virus

HPAI —> H5N1 and other H5 and H7 strains

Paramyxoviridae

A family of negative sense, ssRNA viruses, envlkoped with a non-segmented genome. Replicate in cytoplasm, fragile in evnieonemnt and released by budding. Two major glycoproteins ‘spikes’

• attachment proteins → allows virus to bind to host cell

  • Haemagglutinin-Neuraminidase protein (HN)

  • proteins without neuraminidase activity (G)

• fusion proteins (F) → causes the virus to fuse with the host cell

• glycoproteins DO NOT mutate as readily as influenza

Paramyxoviridae Examples

Hendra Virus —> deadly paramyxovirus found only in Aus

• related to Nipah virus (Asia) = bat → pigs (amplifier) → humans

• reservoir host = bats (flying foxes/fruit bats) + have no symptoms

• amplifier host = horses (~80% mortality, + euthanised if detected)

  • frothy yellow fluid

• dead end host = humans

Nipah Virus —> a rare but highly fatal zoonotic virus causes severe respiratory illness and fatal brain inflammation in humans, primarily distributed across South and Southeast Asia

• bats → pigs → humans (mortality ~30-75%)

• transmission to humans via contact with infected pig excretions

  • also infected date palm sap

    • also human to human transmission

Rhabdoviridae

A family of negative, ssRNA, enveloped, non-segmented genomes that replicate in the cytoplasm in viral factories called NEGRI BODIES.

Rhabdoviridae Examples

Classical Rabies (Lyssavirus) —> infects warm blooded animals with neurological disease

• transmission through biting + saliva

  • also aerosols in caves where bats roost

  • open wounds

  • saliva has lots of virus

• purely neurotropic → only travels through nerves (DOES NOT GET INTO BLOOD)

• zoonotic

• reservoirs = dogs, wild carnivores, bats

Australian Bat Lyssavirus —> neurological disease seen in Australian fruit bats (flying foxes) + micro bats

• transmission through bites/scratches + saliva

Retroviridae

A family of positive sense, ssRNA viruses with an enveloped genome that are very fragile in the environment. RETROVIRUSES ARE RNA VIRUSES THAT INCORPORATE THEIR GENOME INTO HOST GENOME BY CONVERTING TO cDNA. Mutation + recombination occurs at high frequency → lots of variation.

Retroviridae Examples

Feline Immunodeficiency Virus —> Feline AIDS, spread through bites from infected cat + blood sometimes milk from FIV positive queen), viraemia