The laboratory as an aid to clinical diagnosis

The clinician may use the clinical pathology laboratory as a valuable aid to diagnosis and management, for the assessment of response to treatment, and in preventive medicine programs. Each "link in the chain," that is, sample selection, collection, handling, analysis, result reporting, and interpretation must be carefully and efficiently managed, using an informed combination of art and science, to provide a useful endpoint. This general introduction precedes more specific and detailed articles.     

A new approach for the diagnosis of hog cholera

Pestiviruses were isolated from seven cases of suspect hog cholera. Using peroxidase conjugates of monoclonal antibodies (Mabs) six isolates were identified as hog cholera viruses (HCV), while one isolate was of ruminant origin, possibly bovine viral diarrhea virus. In parallel attempts were made to develop an ELISA for the detection of HCV-specific antibodies in pig sera. The Mab HCTC26 coated to polystyrol plates efficiently captured the major viral glycoprotein gp53 from crude antigen suspensions prepared from infected cells. The immobilized gp53 served as diagnostic antigen. Five pigs experimentally infected with the HCV strain Glentorf were sequentially bled and the development of antibodies was monitored by neutralization tests and the ELISA. Results showed that both tests detected antibodies simultaneously after infection. Titres measured by ELISA were slightly higher than those registered by neutralization.     

Transmission of hog hog cholera virus by mosquitoes.

Mosquitoes trapped during an epizootic of hog cholera (HC) in Maryland in 1969 were prepared into 40 pools which were inoculated in pigs. Hog cholera virus was confirmed in pigs inoculated with 8 of 40 pools of mosquitoes. Generally, the pigs contracting HC developed chronic infections with persistent viremia that lasted 30 or more days. Two pigs seemed healthy when euthatized 62 and 80 days after inoculation, yet viremia of high titer was detected in each. Experimental studies were performed with 2 laboratory strains of mosquitoes, Aedes aegypti and Culex tarsalis, to determine if biological and mechanical transmission occur. Biological transmission was not confirmed, but HC virus was retained in A aegypti for 3 days. Mechanical transmission was confirmed with A aegypti in 2 of 9 experiments.     

Use of the agar diffusion precipitation test in the diagnosis of hog cholera

The application of the agar diffusion precipitation (ADP) test for diagnosing hog cholera was investigated. The test used as antigen, pancreatic tissue from 272 pigs that had been inoculated with hog cholera virus. The test was positive for 13.5% of the animals that were sick for 4 days or less, 40% of those sick for 5 days, and 77% of those sick for 6 days or more. The test was positive for 13.5% of all animals that had been vaccinated with crystal violet-glycerol hog cholera vaccine and had been sick for at least 6 days after challenge inoculation.