L. Kirk Clark

Evaluation of antibiotics for the elimination of the tonsillar carrier state of Streptococcus suis in pigs

Seventy clinically normal 13-day-old crossbred pigs from 10 litters from a Streptococcus suis-infected herd were randomly assigned by litter and weight to 7 groups of 10 pigs each to determine whether different antibiotic regimens would eliminate the tonsillar carrier state of S. suis. Six antimicrobial regimens were tested: penicillin intramuscularly (IM) once daily (s.i.d.) for 3 consecutive days; penicillin IM s.i.d. for 5 consecutive days; ampicillin IM s.i.d. for 5 consecutive days; ampicillin per os s.i.d. for 5 consecutive days; ampicillin intranasally s.i.d. for 5 consecutive days; and ceftiofur sodium IM s.i.d. for 5 consecutive days. The seventh group consisted of untreated control pigs. Tonsillar swab samples were collected before treatment, and tonsillar tissue samples were collected after treatment for cultural examination for S. suis. Streptococcus suis was identified in pigs from all groups prior to treatment and after treatment. Pigs did not have clinical signs of disease during the study. All antimicrobial treatments tested in this study failed to eliminate the tonsillar carrier state of S. suis. Early weaning and medication used in this study were not effective for the elimination of the tonsillar carrier state of S. suis in pigs. Optimization of management and environment of pigs coupled with strategic medication of clinically ill animals should be used for control and prevention of mortality caused by streptococcosis.

Ultrastructural observation of the airways of recovered and susceptible pigs after inoculation with Mycoplasma hyopneumoniae

To determine the morphological differences in the epithelium of the airways of recovered and susceptible pigs after Mycoplasma hyopneumoniae challenge, twenty-four 4-week-old M. hyopneumoniae-free pigs were intratracheally inoculated with 107ccu/ml of a pure low-passaged culture of the P5722-3 strain of M. hyopneumoniae challenge material. Eight pigs (group I) were challenged at the beginning of the experiment and rechallenged 3 months later. Group II pigs were also challenged at the beginning of the experiment and necropsied 3 months later. Group III pigs were challenged at the same time as the rechallenge of group I pigs. Eight nonchallenged pigs served as controls (group IV). Three days after the second challenge of group I and the first challenge of group III, and every 3 and 4 days thereafter, two pigs from each group were euthanatized by electrocution and necropsied. Samples of bronchi and lung tissue were examined using light and electron microscopy (SEM and TEM). Macroscopic lesions were observed in the lungs of all group III pigs (average = 4.74%) and were characterized by purple-red areas of discoloration and increased firmness affecting the cranioventral aspect of the lungs. Macroscopic lesions of pneumonia in groups I and II were minimal (less than 1%). There were no gross lesions of pneumonia in control (group IV) pigs. Microscopic lesions were characterized by hyperplasia of the peribronchial lymphoid tissue and mild neutrophilic infiltrates in alveoli. Electron microscopy showed patchy areas with loss of cilia and presence of leukocytes and mycoplasmas in bronchi of susceptible pigs (group III). The bronchial epithelium of rechallenged (group I), recovered (group II), and control (group IV) pigs was ultrastructurally similar indicating recovery of the former two groups. Although mycoplasmas were seen among cilia, a second challenge on pigs of group I did not produce another episode of the disease nor did it enhance morphological changes, suggesting that those pigs could become carriers of M. hyopneumoniae.

Epidemiology and management of selected swine reproductive diseases

Abstract The epidemiology of selected swine reproductive diseases is discussed in relation to herd size and management systems. The reproductive disease agents of major importance in the U.S. are porcine parvovirus, Leptospira spp., pseudorabies virus, swine influenza virus, and porcine reproductive and respiratory syndrome virus. In sow herds, each reproductive disease expresses clinical signs specific to that disease dependent on herd size and management systems, but sick sows, conception failures, resorption of fetuses and abnormal returns, abortion, birth of litters with few pigs, premature births, presence of excessive stillborn or mummified fetuses at term, and birth of weak pigs are the signs usually observed. Dependent on the disease present, individual sows express clinical signs related to the time during the reproductive cycle they are infected. The clinical expression of these diseases in individual sows and in herds can be used as an aid to diagnosis. Vaccines are available for all the diseases listed, but protocols for effective use of vaccines for influenza and porcine reproductive and respiratory syndrome are subject to further investigation.