[New taxa in Psoroptinae. Hypothesis on the origin of the group (Acarina, Sarcoptiformes, Psoroptidae)]

The author describes three new species and one new genus in the family Psoroptidae, subfamily Psoroptinae. A key is given to all the known genera of this subfamily. The fact that amongst the 16 species known from Africa South of the Sahara, 9 are endemic incites the author to believe that this group has a Centro-african origin.

Growth of Nosema cuniculi in established cell lines

Growth patterns of Nosema cuniculi (Encephalitozoon cuniculi) in cell cultures of bovine kidney, canine kidney, feline lung, and rabbit kidney were studied. All cell cultures used were easy to manage and the last 3 are commercially-available established cell lines. The dog kidney cells were the most suitable for large-scale production of Nosema. When grown in plastic flasks with a bottom area of 75 cm2, the weekly yield from Nosema-infected canine kidney cells during the 10th to 17th week after inoculation was between 4-1 times 10-7 and 9-9 times 10-7 spores per flask. An equilibrium was obtained between the Nosema infection and the kidney cells during this time. A simple method for estimating the number of harvested spores is also described.

Further studies on tularemia in Alaska: virulence and biochemical characteristics of indigenous strains

Cultures of Francisella tularensis isolated in Alaska were compared on the basis of their virulence and biochemical characteristics. Isolates from the hare, Lepus americanus Erxleben, and the hare tick, Haemaphysalis leporispalustris (Packard), conform to the description of F. tularensis nearctica Ols. in their ability to kill domestic rabbits, guinea pigs, and white mice, and in their ability to use glycerol and DL-citrulline. A rodent isolate conforms to the description of F. tularensis holarctica Ols. in its inability to kill domestic rabbits or guinea pigs, and in its inability to use either glycerol or DL-citrulline. Observations of hares experimentally infected with the hare isolate indicate that: (1) they may be fatally infected with less than 10 microorganisms; (2) the infection is fatal within 9 days; (3) no macroscopic lesions are apparent.

Effects of variations in temperature on infective larvae and their relationship to inhibited development of Obeliscoides cuniculi in rabbit

The relationship between changes in the temperature of storage of infective O. cuniculi larvae and the proportion that become inhibited in a subsequentinfection was studied. Prolonged storage at 5°C resulted in an initial inhibitionfollowed by acclimation to this temperature and subsequent normal developmentin the host. After acclimation to low temperature raising the temperature ofstorage produced no appreciable increase in the proportion of worms inhibited atthe early 4th stage. Maintenance of infective larvae at 15°C followed by a suddendecrease in storage temperature to 5°C resulted in rapid onset of inhibition. This inhibition was not reversed even after 25 days at the lower temperature. These temperature variations and the consequent pattern of arrested development werecompared to seasonal changes of spring and autumn occurring to nematode larvaeon pasture. An increase in the number of larvae given from 5000 to 15000 perrabbit had a slightly significant effect upon the proportion that remained inhibited. The need for careful assessment of the methods used for determining the extentof such inhibition is discussed.

The interaction between the immune response of rabbits to heterologous antigens and a primary infestation with Rhipicephalus evertsi evertsi

Rhipicephalus evertsi evertsi feeding on hosts inoculated with sheep red blood cells (SRBC) and bovine serum albumin (BSA) suppressed the primary antibody response to the two antigens. In addition, while the ticks paralysed most hosts in the studies, fatality associated with this toxicosis occurred only in rabbits which had received SRBC, either alone or with BSA. Only those hosts inoculated with BSA developed any resistance against the ticks, manifested by a slight reduction of engorged weights and development of anti-tick antibodies. These results suggest that R. e. evertsi infestation induces a degree of reduced host immune responsiveness to heterologous antigens.