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Immunity in Canine, Piroplasmosis 
2. The duration of “ immunity ” following “ recovery 
Whilst dealing with the subject of immunity in canine piroplasmosis 
it appears to us advisable to include a discussion on certain problems 
which have arrested our attention in the course of our investigations. 
We shall first consider the matter of the partial immunity which follows 
upon the subsidence of the acute manifestations of piroplasmosis, a con¬ 
dition in which the animals are referred to as “ salted ” or “ recovered.” 
Both in the European and African disease immunity is stated to last 
for some time after recovery. Lounsbury (1901, p. 11) believes that 
under natural conditions the acquired immunity is maintained by 
“continuous infestation by ticks.” According to Nocard and Motas 
(1902, p. 277) naturally acquired immunity and that following the 
disease induced by inoculation lasts as long as 6 months in the European 
disease. Robertson (vi. 1906, p. 113) states that under natural condi¬ 
tions one attack does not protect for life and that dog owners at the 
Cape state that dogs may have three or four attacks. In Robertson’s 
experience one attack usually “ permanently salts ” a dog, but he has 
seen four cases in which dogs recovered one season and died from con¬ 
tracting the disease in the following season. This author has observed 
an instance, unique in his experience, where a dog acquired the disease 
three weeks after it had passed through a severe attack and its tempera¬ 
ture had returned to normal. The second attack followed the injection 
of 5 c.c. of virulent blood and the dog succumbed to the infection. He 
has on the other hand proved that salted animals may resist blood 
inoculation and tick infection for a considerable period. Lounsbury 
(1901, p. 11) reports the case of a dog which died from the disease, 
having suffered from it two years previously. 
It is difficult to judge of the value of these statements as the term 
immunity is usually employed in a loose sense. Properly speaking, an 
animal can only be described as immune when it no longer harbours a 
parasite and is at the same time resistant to reinfection with the same 
species of parasite. It is clear from what we note below with regard 
to the persistence of the parasites in the blood of apparently recovered 
or “ salted ” dogs, that animals are frequently termed immune when, 
strictly speaking, they are suffering from chronic piroplasmosis, from 
which it is true they may ultimately recover. It is possible, as Louns¬ 
bury suggests, that continuous reinfection through the agency of ticks 
maintains the acquired “ immunity ” since when reinfection ceases and 
the parasites disappear the animal again becomes susceptible. In other 
