A quote from this paper on biological warfare programs against humans implies fleas were seriously considered to spread disease between humans. Any flea will bite a human if its normal host is not available.

"The Japanese and American biological warfare programs in the mid-twentieth century included experiments on how to breed and disseminate mosquitoes and fleas. This is more difficult to achieve on a large scale than aerosolisation and has fallen out of favour. There are so many agents which can be aerosolised that it would be unusual now to spend the time breeding insect vectors and keeping them alive in readiness for a biological attack. Iraqi scientists tried putting biological agents in missiles, planning to disperse them with the blast of an explosion. This is not a very effective method as the heat and blast of the explosion would kill most of the organisms and others would be driven into the ground rather than dispersed through the air."

In contrast with most people not wanting to spread diseases or parasites that carry diseases such as plague, here we have an example of Australian Governments spreading diseases such as Myxomatosis and Rabbit Hemorrhagic Disease and deliberately introducing foreign parasites eg the rabbit flea, to spread such diseases (and we don't know what other diseases may be spread by fleas and such between other species they may choose to bite).


Rabbit Control - Myxomatosis
http://www.dpiwe.tas.gov.au/inter.nsf/WebPages/RPIO-4ZP3EF?open
Agdex 671
Number 241
ISSN 0159-2971

Myxomatosis is a viral disease fatal only to the European rabbit. It will infect other species of rabbits and hares but not kill them, and it has no effect on any other animal species.

The disease occurs naturally in South America and only mildly affects the local rabbit species.

Australian research in the 1920s and 1930s examined myxomatosis as a rabbit control agent but it was not until 1950 after work by CSIRO scientists that myxomatosis was released for this purpose and began spreading rapidly through the Murray River valley.

The virus was a successful control agent and soon spread to many areas of Australia. By 1953 more than 90 per cent of the rabbits in Australia had died of the disease.

The original virus killed about 99 per cent of infected rabbits, which died within 12 days. But as other less virulent strains developed the mortality rate fell. The strain which now predominates in the field kills up to 70 per cent of infected rabbits. Infected animals remain alive for up to one month and therefore spread the disease for a longer period than animals with the more virulent strain.

Myxomatosis is a disease of the skin and the mucous membranes. The symptoms are swollen and discharging eyes, swellings on the skin at the infection site and in the ano-genital area and a high temperature.

Myxomatosis is more severe in cold weather. A field strain infection kills around 70 per cent of susceptible rabbits in winter but only about 30 per cent in spring or summer.

When a rabbit is infected with myxomatosis its body produces active antibodies in an attempt to kill the virus. Usually the rabbit dies but if it recovers it will have a high level of antibodies in its blood and they will protect the animal from further infections of the disease.

Rabbits with such immunity, when pregnant, can pass on some antibodies to their young so that the kittens are born with the same level of immunity as their mother. This is called passive immunity and the protection only lasts about seven weeks.

If a young rabbit with passive immunity is infected by a field strain of myxomatosis its antibodies will either kill the virus rapidly so that no active antibodies are produced and the animal remains susceptible to further infection, or the antibodies will slow down the virus and so allow active antibodies to be produced. This leaves the young rabbit immune to further infection from myxomatosis. The response will depend upon the degree of the passive immunity and the virulence of the virus involved.

The effectiveness of myxomatosis is further reduced by an accumulation of genetic resistance within the rabbit population. This is a lifelong protection and it will continue to gain strength and allow more rabbits to survive.

The most important agents involved in the transmission of myxomatosis are mosquitos and fleas.

All species of mosquito will transmit the disease from one rabbit to another but some mosquito species are particularly effective. The most rapid spread occurs with mosquito species that are active in the evening, feeding from several animals rather than engorging on a single animal. Some species of mosquito can infect up to 10 rabbits after biting one infected animal. At normal temperatures a mosquito can remain infective for four weeks and in cold conditions they can remain infective for up to seven months.

Because mosquitos are not active all year or under all conditions the European rabbit flea was introduced as a vector in 1969.

This flea, which can only breed on pregnant rabbits, readily spreads myxomatosis as it moves from rabbit to rabbit. The fleas can live on pasture for 2-3 weeks or in empty burrows for several months. They provide a reservoir of infection. (Young rabbits can become infected with myxomatosis soon after birth). However, the presence of fleas on a rabbit does not mean that it has myxomatosis. Rabbit fleas can also live on other animals (on cats for example), but they do not spread any disease to animals other than rabbits.

Rabbit fleas are most abundant during the rabbit breeding season. They can be collected by shooting some rabbits and combing their fleas with a fine-toothed comb into a container. About 50 fleas can be placed in the entrance of any active burrow. Fleas that are introduced to a rabbit population in June should be well established and plentiful by November - the major rabbit breeding time of year.

Rabbit fleas are present in most parts of Tasmania but it is necessary to check small local rabbit populations to ensure their presence before introducing myxomatosis.

As the field strains of myxomatosis are no longer as virulent as the original releases the disease can no longer be considered a reliable control agent for rabbits. But in some years it is a valuable aid. Any outbreak of myxomatosis that reduces rabbit numbers can be used as a base for further reductions through poisoning, fumigation, warren ripping or cover removal.

When poisoning is impractical, a virulent strain of the disease can be introduced to a specific area. Its success depends on a large rabbit population, the absence of field strain myxomatosis since before the previous breeding season and the presence of rabbit fleas to spread the disease.

Rabbits infected with the disease can be caught in one area and released in another if necessary but, upon release, they are disorientated, are not accepted by local rabbits and can rapidly become victims to feral cats or birds of prey.

Releasing a virulent strain of myxomatosis does not guarantee that an outbreak will occur. There may have been a non-virulent strain previously endemic in the area giving immunity to the majority of rabbits present. Alternatively, other conditions may cause infected rabbits to die before they can transmit the disease to others.

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