Neospora

• 2 main species
  • Neospora caninum in the dog
  • Neospora hughesi in the horse

• Sporulated oocysts measuring just 10μm

• Oocyst contains 2 sporocysts with 4 sporozoites

• Route of transmission not fully understood

• Often misdiagnosed as Toxoplasma gondii
  • Sarcocystis cysts have thicker walls

• Infection diagnosed by IFAT, ELISA or PCR
  • Identification of lesions and organisms in tissue using immunohistochemical staining
  • Eliminate other causes of abortion first

Life cycle

• Life cycle similar to Toxoplasma gondii

• Limited range of warm-blooded intermediate hosts
  • Asexual reproduction occurs in intermediate host forming tissue cysts

• Host range of sexual stage is unknown for N.caninum
  • Intermediate host for N.hughesi is the horse, but the definitive host is unknown

• Final host
  • Dogs pass oocysts
  • Role not fully understood in pathogenesis
  • 5 day prepatent period
  • Other wild canids may also act as final definitive hosts

• Intermediate host
  • Mostly cattle
  • Natural infection has been documented in other herbivores

• Transmission
  • Transplacental infection occurs in all intermediate hosts and in the canine final host
    • Transplacental transmission can occur in successive pregnancies
  • In cattle, vertical transmission occurs
    • Post-natal infection occurs but is less common

Pathogenesis

• Dogs
  • Occurs mainly in puppies
  • Causes ascending paralysis, especially of hind limbs, with muscle wasting
  • Causes sudden collapse due to myocarditis
  • More than 1 puppy in a litter may be affected, although this may not occur simultaneously
  • Successive litters affected

• Cattle
  • Commonest cause of infectious abortion in dairy cattle
  • Congenitally infected calves can have encephalomyelitis and paresis
  • Abortion usually occurs between 5-7 months of gestation but can occur as early as 3 months
  • No other clinical signs in the cow
  • Repeat abortions possible in same cow (persistently infected)

• Horses
  • Myeloencephalitis
  • Transplacental infection occurs
  • Disease only diagnosed in USA

• Neospora caninum in myositis

Prevention and Control

• Do not allow dogs access to calving cows, placental membranes and aborted or dead calves

• Do not allow dogs to defecate in cattle feeding areas

• Identify and cull seropositive cattle, or do not breed from them or their progeny

• Select seronegative cattle for breeding

• Vaccinate
  • Only in the USA
  • Neoguard or Intervet
  • Killed protozoal vaccine for healthy, pregnant cows
  • Dosed in first 3 weeks of pregnancy and then every 3-4 weeks during gestation
  • Revaccination with 2 doses during each subsequent pregnancy