Relationship between two serotypes of avian mycoplasmas by serological and DNA-DNA hybridization tests.

Genetic relatedness among eight strains of avian mycoplasmas representing two serotypes, C-O and D-P, was determined using DNA-DNA hybridization tests. One strain from each serotype was found to be misclassified. The average percent homology between the two serotypes was 34.1% at 56 C and 18.6% at 66 C. The average homology among the four C-O organisms was 99.6% at 56 C and 93.5% at 66 C, while among the four D-P strains the average homology was 91.6% at 56 C and 92.2% at 66 C. These relationships correlated with antigenic cross-reactions observed in complement fixation (CF) and fluorescent antibody (FA) tests. Thermal denaturation of the pure DNA from each strain resulted in base compositions of 25.0 to 28.2 moles percent guanosine plus cytosine (GC). Thermal denaturation of selected hybrid DNA revealed a linear relationship between percent homology and delta melting temperature (1 C delta Tm for 15% difference in percent homology). Thirty-four percent homology between the organisms of C-O and D-P serotypes indicates a minor antigenic relationship; thus, it is recommended that these two serotypes be retained as separate groups.

Passive haemagglutination test for antibodies against rabies virus.

All the procedures now available for the measurement of rabies virus antibodies in serum have certain disadvantages. The serum neutralization test (SN), whether carried out by assay in mice or by the plaque-reduction technique, requires several days before the titrations are completed, necessitates special facilities for keeping large numbers of animals and tissue-culture plates, and is relatively expensive. A complement-fixation test is very insensitive, giving low titres in comparison with SN tests, and a haemagglutination-inhibition procedure is complicated by the presence of nonspecific reactions. A rabies passive haemagglutination technique (RPHA), developed to overcome many of these problems, is described.Titres obtained with human sera by the RPHA procedure correlated well with those obtained by SN tests. Both IgG and IgM classes of antibodies were measured by the RPHA procedure; however, it appeared to be more sensitive for detecting IgM than was the SN test and, therefore, gave higher titres for this class of immunoglobulins.

Effects of homologous or heterologous antiserum on neutralizing-antibody response to rabies vaccine.

Heterologous antirabies serum is commonly used in the treatment of persons exposed to rabies. However, the high incidence of serum sickness which accompanies its use has prompted work to develop a homologous human product. As human antirabies serum is expensive and difficult to obtain in large quantities, a series of experiments was done on guinea-pigs to test the effects of homologous and heterologous antirabies serum.Similar amounts of homologous and heterologous antisera administered to guinea-pigs produced similar circulating neutralization titres one day later. The homologous antibody titres, however, decreased more slowly than the heterologous antibody titres.When homologous antiserum was given, followed by duck-embryo rabies vaccine, an apparent response to the vaccine was suppressed or delayed longer than when heterologous antiserum and vaccine were administered. However, when homologous antiserum was given with suckling-mouse-brain vaccine, of a much higher potency, the response to vaccine was apparent in the presence of a passive titre of 1:120.If a similar relationship is seen in man with the use of a homologous antirabies product, it will be essential to use high potency vaccines or alter the established vaccination schedules in order to overcome the inherent interference problems.

Isolation, characterization, and pathogenicity studies of a bovine respiratory syncytial virus.

The isolation and characterization of a bovine respiratory syncytial (RS) virus is described. Serological studies indicate that bovine RS virus is widespread in Iowa cattle and that it is involved in some outbreaks of respiratory disease. Experimental infection in calves indicates that the virus can cause illness in calves, particularly those with serum neutralizing antibody.

A bovine adenovirus type 3: isolation, characterization, and experimental infection in calves.

A virus was isolated from a group of feedlot cattle with acute respiratory disease that was characterized by physicochemical methods as an adenovirus and identified serologically as a bovine adenovirus type 3. Intratracheal inoculation of three 4 month old colostrum deprived calves resulted in pyrexia, hyperpnea, dyspnea, anorexia and in one animal a mild diarrhea.

Rabies group-specific ribonucleoprotein antigen and a test system for grouping and typing of rhabdoviruses.

Cell-associated ribonucleoprotein (RNP) was isolated from BHK-21 cells infected with several strains of rabies and rabies-related viruses. The RNP-antigen from rabies and related viruses induced the formation of complement-fixing, precipitating, and immunofluorescent antibodies, and proved to be the group-specific antigen common to all rabies viruses. Antigens of the envelope which induce virus-neutralizing antibodies are apparently determinative for the serotype of a virus as evidenced by two-way neutralization tests. A combination of these methods seems to be a useful approach to the serological grouping and typing of rhabdoviruses.