A study on ectoparasites with special reference to chigger mites on rodents/shrews in scrub typhus endemic areas of Kerala, India

The main goal of this investigation was to record the ectoparasites living on rodents in scrub typhus endemic areas of Kerala state, India. Rodents captured alive using Sherman and wonder traps from four diverse habitations revealed, a total of 59 rodents/shrews constituted by 5 host species from families Muridae and Soricidae. In total, 1135 ectoparasites were collected on these rodents/shrews and were identified representing 23 species from 10 genera in 4 families Trombiculidae, Laelaptidae, Ixodidae and Pulicidae. Dominant insectivore species was Suncus murinus (57.6%). 42 (71.2%) rodents and shrews were found to be plagued with at least one of the 23 species of ectoparasite harvested. Mites belonging to the family Trombiculidae were the predominant ectoparasite species collected. Study revealed Tatera indica (35.5%) as the primary host harboring the chigger mites. Xenopsylla cheopis and Xenopsylla astia the flea species important vectors for the transmission of zoonotic diseases such as Leptotrombidium deliense, Schoengastiella ligula and Echinolaelaps echidninus were recorded. Twenty species of mites were reported for the first time in Kerala which add knowledge on the ectoparasites distribution.

The Effect of Temperature and Humidity upon the Survival of Certain Unfed Rat Fleas

Previous work on the effect of temperature and humidity upon the survival of unfed fleas is criticised in respect of experimental technique. In the present investigation measures have been taken to eliminate as many variables as possible and the methods employed to this end are described.In the experiments, 2027 Xenopsylla cheopis, 999 X. astia and 646 Ceratophyllus fasciatus were employed, all unfed and less than 24 hours old at the commencement of the different experiments. Records were kept individually so that a statistical measure of consistency could be made.The following conclusions have been reached:(1) Duration of life of unfed fleas is not influenced by sex.(2) High temperatures and low humidities tend to shorten life; conversely, low temperatures and high humidities, with a possible optimum of about 90 per cent., tend to produce longer lives.(3) Humidity is at its maximum efficiency in this respect at about 18° C.(4) At 37° C. humidity ceases to have any effect upon the duration of life of unfed fleas, and the evidence suggests that there is also a low temperature at which humidity has no influence upon survival.(5) There is no direct proportion between survival of unfed fleas and saturation deficiency of the atmosphere at any temperature.Comparing the species, it was found that:(1) Ceratophyllus fasciatus was the longest lived, at similar atmospheric conditions.(2) Xenopsylla astia lived longer than X. cheopis at all humidities at 23° C.

Bairamlia fuscipes Waterston, a Chalcidoid Parasite on Ceratophyllus wickhami Baker (Siphonaptera)

The Chalcidoid wasp, Bairamlia fuscipes, was found parasitising the flea Ceratophyllus wickhami in the nest of the North American Grey Squirrel (Sciurus carolinensis) from Gerrard's Cross.The larval and pupal stages of B. fuscipes were found in the cocoons of C. wickhami, and the adults were crawling about in the squirrel's nest.The parasites were scarce, only 7 per cent, of the cocoons dissected at intervals during fifteen months were parasitised.The parasite has not been reared in the laboratory beyond the second instar larva, though full grown larvae have successfully reached maturity under experimental conditions.B. fuscipes oviposits through the flea cocoon and fixes the egg on the abdomen of a resting larva or pupa. Only one egg has been found in each parasitised cocoon. The larva feeds externally on the flea, fixing itself to the fourth abdominal segment or thereabouts.Attempts were made to parasitise larvae of Xenopsylla astia, but without success.The external anatomy of the full grown larva of B. fuscipes is described.

Plague Fleas, with special reference to the Milroy Lectures, 1924.

The geographical distribution of the different species of rat flea is one of the most important factors governing the spread of plague.Xenopsylla cheopis is the most effective transmitter of both epidemic and epizootic bubonic plague in all parts of the world.The relative immunity of certain parts of India and Ceylon from plague is to be primarily attributed to the prevalence of an inefficient plague-carrying flea on the rats of these localities, viz. Xenopsylla astia.Climatic conditions play only a secondary part in limiting the spread of the disease in these relatively plague-free localities.Plague infection can be maintained in such localities by the importation of cheopis-infested merchandise.Climate does not exert an equal effect upon the transmitting power of different species of flea.Numerous attempts to transmit plague from rat to rat by means of X. astia at room temperature during the plague season in Colombo have all failed. X. astia, however, can carry plague from rat to rat under climatic conditions favourable to plague transmission. Continuous transmission of plague from rat to rat has been obtained with X. cheopis in Colombo under exceptionally unfavourable climatic conditions.Both plague and X. cheopis have a very irregular distribution within limits of Colombo City. The coefficient of correlation between two periods of human plague incidence and percentage of cheopis to total rat fleas of all species in 14 districts of the city is ·95, probable error ± ·02 for both periods.There is a close relation between premises infested with X. cheopis and premises where plague-infected rats are found.A three-fold relationship exists between the amount of imported grain, the prevalence of cheopis on rats, and the incidence of plague in the localities where grain is stored in Colombo.The measures so far devised for combating plague among Oriental populations, tolerant of all forms of animal life, have not proved conspicuously successful.Due recognition of the importance of the flea species factor should lead to marked improvement in plague preventive measures in many parts of the world.A rat flea survey of all the principal plague areas, especially the ports, becomes urgently necessary.The exports from localities where X. cheopis is found to be prevalent upon the rats should be considered actively dangerous when the locality is plague infected, and potentially dangerous even if it is plague free, since the continual importation of cheopis into a locality where this flea is not indigenous may eventually result in the extension of plague infection to a new area.I agree with Glen Liston and Norman White, that the export of produce, especially grain, from plague-infected ports should be controlled by international agreement.The limitation of imported cheopis and plague to definite zones in such localities as Colombo greatly facilitates the task of plague prevention, since all available resources can be concentrated simultaneously, or successively, on the infected areas.In such instances it is possible to mark out the potentially plague-infected zones by the simple and accurate method of surveying the rat fleas.Ten years have now elapsed since I tentatively put forward the suggestion that the spread of epizootic plague in the East Indies might be governed by the flea species factor. At first I adopted a cautious attitude towards my own hypothesis. I believe that the evidence now available warrants its acceptance by epidemiologists without further hesitation.If so, the discovery is but further testimony to the essential unity of science in its bearings on the welfare of the human race, for it is the natural outcome of the purely zoological researches of Rothschild and Jordan on the systemics of the Siphonaptera.