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A new formulation of yellow fever virus vaccine incorporating a stabiliser has been prepared which is very much more stable than conventional unstabilised vaccines. This vaccine has a half life of 2-4 years at 4 degrees C, 9 months at 20 degrees C and 10 days at 37 degrees C. Its greater stability should have considerable advantages, especially when it is used in tropical countries.
Female Aedes aegypti mosquitoes infected with yellow fever virus by intrathoracic inoculation transmitted the virus to a small percentage of their F1 progeny. Infected offspring were obtained from surface-sterilized as well as from untreated eggs, indicating that the virus was transovarially transmitted. Vertical transmission of yellow fever virus in mosquitoes may be an alternative mechanism for biological survival of the virus during adverse periods or in the absence of susceptible vertebrate hosts.
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During the production of yellow fever virus 17 D vaccine from chick embryos, few embryos die in the time between injection of the eggs and harvest of the embryos. In order to answer the question whether the death of the embryos is due to the infection or to the injury caused by the injection, it is necessary to examine the embryos macro- and microscopically for pathological changes. 8 and 9 days old chick embryos were inoculated into the amniotic cavity with different concentrations of yellow fever virus 17 D (table 1). The embryos were removed from the eggs between the 2nd and 7th day after inoculation. Heart, lung, kidney, brain, liver, and spleen were removed. Macroscopically observable pathological symptoms of the embryos and their organs were recorded. Sections of the organs were histologically investigated. Some embryos died soon after the infection, others on the 5th and 6th day of incubation (table 2). Their death was dependent on the dosage of the inoculum. Macroscopically, some embryos showed oedemas, petechiae on head and trunk, haemorrhages of liver and kidney, enlargement of liver and spleen, and a yellow discolouration of the liver (table 3). Microscopically, liver and brain showed the greatest pathological changes; heart and kidney were also affected, whereas lungs and spleen seemed to be unaffected. The following pathological changes were observed: slight fatty degeneration, oedemas, vascular inflammation, perivascular infiltrates, diffuse infiltrations, infiltrations in form of small nodules and necroses (table 3 and figures 1-12). the severity of the symptoms was evaluated using arbitrary units. These units are summarized on table 3 according to time of occurrence p.i., to virus dilution, to organ, and to type of symptom. An index of pathological changes was allived by dividing the sum of units by the number of organs. The maximum value of the index was demonstrable in liver and brain (table 4). Figure 13 adn table 5 show the development of the lesions during the infection. The maximum value of the index was reached on the 5th day p.i. The most significant pathological changes, as necrosis and perivascular infiltrate, were mainly observed from the 5th day p.i. on (table 6). The perivascular infiltrates were found in heart and brain, the necroses in brain and liver (table 7).
Three geographical strains of Aedes aegypti from Thailand (Amphur), East Africa (Kampala), and the West Indies (Santo Domingo) were compared for susceptibility to infection with low-passage yellow fever virus (French viscerotropic) as well as for ability to transmit virus by bite at varying extrinsic incubation periods. Santo Domingo strain appeared the most competent and Kampala the least when mosquitoes were exposed to a low level virus-infecting blood meal; at higher virus levels, a similar trend was noted but differences were less evident and in no case were the differences statistically significant. All three strains were infected with and transmitted yellow fever virus.
The yellow fever virus is isolated in natura from eggs of a Tick Amblyomma variegatum. It is then isolated from larvae issued from the same egg-cluster and also from blood of a monkey bitten by larvae of the same origin. It is reported that the same virus has been previously obtained from adults of the same species of Tick. An acarine appears for the first time as a sylvatic vector and reservoir (at least temporary) of yellow fever.
The behavior of 1,072 mice that had recovered from encephalitic infection with intracerebrally injected yellow fever virus 17D and of 216 normal mice was tested in a maze and on a horizontal rod rotating around its axle. Infected animals needed more time (average, 8.90 min) to find their food in a maze than did normal animals (average, 4.37 min). Infected mice were able to stay on the rotating rod for a shorter time (average, 6.4 seconds) than were normal animals (average, 9.0 seconds). The correlation between the concentration of virus injected and the performance of the mice was confirmed by the extent of lesions found by histologic study: animals that had anatomic lesions after surviving encephalitic infection showed abnormal behavior.
Dengue-immune rhesus monkeys were challenged with a South American and two African strains of yellow fever virus. Levels of viremia were reduced as compared with control nonimmunized monkeys. The results support the hypothesis that immunity to dengue in a human population acts as a barrier to establishment of yellow fever in that population.
During an epidemiological survey of yellow fever in Eastern Senegal, one strain of yellow fever virus was isolated in December 1976 from wild Mosquitoes. This first isolate obtained in nature from Aedes subgenus Diceromyia shows the primordial part these vectors may have in the area studied. It corroborates the existence of a selvatic focus of yellow fever in this region. It also gives information on the transmission cycle in a dry area.
A cell culture from brains of one day old mice was infected with a high multiplicity of the French neurotropic strain of yellow fever virus (FNV); the infected cell culture produced and released infectious FNV for more than 180 days post-inoculation with titres between 10(0.6) and 10(6.4) PFU/ml. The cell sheet exhibited some rare plaques of round cells with a slow centrifugal extension; the destruction of the cell sheet was not complete before 200 days post-inoculation.
Aedes (Finlaya) notoscriptus (Skuse), a mosquito which occupies a similar ecological niche to Aedes (Stegomyia) aegypti (L), the urban vector of yellow fever virus, was screened as a possible vector of this disease. The results indicate that almost certainly Ae. notoscriptus is refractory to the virus and could not act as a vector if yellow fever were introduced to Australia.
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A simple, rapid and inexpensive method of isolating yellow fever (YF) virus from naturally infected mosquitoes, human liver and the serum of a sentinel monkey by inoculation of a continuous line of mosquito cells is described. The mosquito cells were more sensitive than suckling mice and marginally better than Vero cells for primary isolation. This is the first time that mosquito cells have been successfully used for primary isolation of YF virus from field material.
Glycosaminoglycanpolysulfates (GAGPS) have virus inhibiting properties demonstrable by means of tissue culture in the plaque method. In brain preparations of children who had died of a hyperpyretic toxicosis, cell necroses were found corresponding to the picture of tissue culture plaques. The question arose from these observations whether this inhibiting effect of GAGPS can perhaps also be demonstrated in vivo. In animal experiments, cell necroses corresponding to those of the infant brain could be observed during the course of a 17 D yellow fever encephalitis in mice. The Luitpoldt-Werk Munich placed to our disposal 13 different GAGPS for tests. Each of these substances was tested in 210 mice (fig. 1). Virus dilutions (LD 50/ml) were mixed to the same volume with the indicated concentrations of substance directly before vaccination. The differing LD 50 doses is due to the fact that each ampoule contains a different content of virus.) The toxicity of all substances is practically zero (table 2a, 2b). The effect of the inhibiting substances was evaluated at first by means of a deviation of the rate between alive and dead animals (table 1). The statistical significance of the effect of some substances was that high so that an inhibition of the virus replication has obviously to be considered. The significance for L1 and L4 - they are chemically very similar - is higher than 0.001 (table 4). The virus inhibiting effect of the substances was controlled by histopathology. 31 brains of mice were dissected and histologically evaluated; the lesions of the brains were examined and recorded (table 3). The effect of the substances was measured by absence or diminution of the lesions. The most effective substance was L1 as far as its concentration was higher than the critical limit of 625 gamma/ml.
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