2 BULLETIN 36, PUERTO RICO BXPERIMEX1 STATION 
DAMAGI in i-ak LBITEfl 
llic seriousness of parasites depends on the kind or kinds and the 
numbers present as well as the Length of time the animals are in- 
fested. Parasites may cause injury or death to the bost in one or 
more of the following ways: (1) Loss <d* blood; (2) interference 
with digestion ; (3) damage or destruction of tissue ; I i) secretion or 
excretion of toxins which may be absorbed by the h< con- 
stant irritation, itching, pain, etc.; (<>) transmission <d' dis< 
directly or indirectly. 
The death rate from parasitic infestations may uot he high, but 
results from slow and stunted growth, uneconomical use of iwd. 
Lowered capacity for work, reduced production, and condemnation of 
the meat carcasses in whole or in part. A heavily parasitized ani- 
mal Is likely t<> be more susceptible t<> bacteria] injections and other 
diseases, and such an animal becomes a " poor risk " when treatment 
is attempted with drugs and biologies. 
SUSCEPTIBILITY TO PARAS1 I i - 
The damage from parasites is greatest as a rule among young 
animal-, as they seem to become more easily infested than older 
animal.-, and young tissues are more easily injured. As growth must 
be made in youth and cannot be made up later, it i- important to 
pay special attention to the care of young >tock. 
In Puerto Rico calve- suffer more from parasites than from dis- 
eases due to other causes, with the possible exception of morbid col 
ditions caused by improper feeding. Mature cattle are injured by 
externa] parasites and protozoan diseases, hut are Less susceptible to 
the worm parasites. The liver fluke seems to he the only serious 
worm parasite <>f older cattle. 
SYMPTOMS OF PARASITISM 
The symptoms of parasitic worm diseases are usually less noti *- 
able than those from infectious diseases caused by bacteria, because 
the onset is seldom noticeable and the symptoms are usually more 
vague. The presence of worm parasites may he suspected where 
there is a lack of growth or a loss in weight, distended abdomen, and 
diarrhea or constipation with little or no fever. 
Anemia and edema are characteristic of the bloodsucking para- 
sites. Anemia is shown by thinness of the blood and paleness or 
whitening of the mucous membranes revealed by examining the in- 
side of the mouth and inner surface of the eyelid-. Edema i> a 
swelling caused by an accumulation of fluid in the tissues, usually 
m the pendent portions of the body such as underneath the jaw or 
in the lower abdominal region. Heavily parasitized work animals 
such as oxen and horses tire easily and frequently are unable to 
stand heavy work. 
Protozoan diseases are more like specific bacterial diseases in that 
they usually run a more definite and acute cour-e and -how charac- 
teristic symptoms. Stockmen are more or less familiar with the 
arthropod- or external parasites and the injuries produced by them. 
