Poxvirus infection in a rat (Rattus norvegicus) in Kuwait.

A poxvirus was isolated from skin lesions on the tail of a rat (Rattus norvegicus) in Kuwait in February, 1982. The virus grew on the chorioallantoic membrane (CAM) developing chicken embryos and induced small generalized haemorrhagic pock lesions, 72 hours post-inoculation. It grew also with cytopathic effect (CPE) in CER and Vero cell lines. In cultured cells it produced cell rounding and syncytia 48-72 hours post-infection. The virus was resistant to the effect of ether as well as to chloroform, and showed haemagglutinating activity against chicken red blood cells in a low titer (1:16). It induced in the rabbit skin nodular lesions 4-5 days post-infection. Electron microscopy of the negatively stained preparations revealed brick-shaped typical poxvirus virions measuring 220-250 millmicron in diameter. By using vaccinia antiserum the virus antigen was precipitated in the agargel immunodiffusion test and this indicates its relation to the genus Orthopoxvirus.

Effects of sublethal doses of DDT on the reproduction and susceptibility of Culex pipiens L.

The effect of non-selecting doses of DDT on the induction of resistance was investigated in the house mosquito, Culex pipiens. Sublethal doses of DDT were applied to the adults in each generation, at levels which just fell short of causing mortality in these adults. A susceptible strain, a DDT-resistant strain, and a slightly DDT-tolerant strain were so treated for 6-7 generations.It was found that the treatment initially caused approximately 25% of the ovaries to degenerate, and reduced the proportion of females that fed and oviposited. This reduction in biotic potential became aggravated in successive generations of the DDT-resistant and DDT-tolerant strains, which failed to show any material increase in resistance level. In the susceptible strain, however, the biotic potential became enhanced, and considerable resistance was developed. It was concluded that the increase of resistance in this strain was due to hidden selection, of eggs in the ovary, and of females which failed to oviposit.