Like the flies mentioned in the previous section, cockroaches too have been implicated in the mechanical transmission of enteric disease. Fewer species of cockroach are involved as the vast majority are found free-living in forests and grasslands and are of no medical or public health importance. Only the peridomestic species that have successfully adapted to the human environment are considered here.
Fewer studies have been conducted with cockroaches to establish their role as vectors. Nevertheless, their role as mechanical vectors Is great.
The reasons for this are as follows:
Cockroaches do not have a seasonal incidence, therefore their ability to transmit disease remains undiminished throughout the year.
Their preference for a warm, humid and temperature-controlled environment, such as a kitchen or hospital, enhances their contact with pathogenic micro-organisms.
The immature stages of cockroaches share the same habitat, behaviour and food requirements as the adult and are of equal status as efficient vectors, whereas only adult flies have been implicated.
Being an indoor pest, cockroaches seldom venture outside and so share a close association with humans.
Cockroaches are long-lived insects. The period from first-stage nymph to adult may be in excess of twenty months, depending on the species involved.
The pest species involved are largely nocturnal and their presence often goes unnoticed.
In temperate climates cockroaches tend to crawl more than fly. Their contact time with contaminated material is then increased.
Studies using cockroaches have clearly established their ability to come into contact with and eat human faecal matter and infected material. Comparative studies on the micro-organisms found in the environment from which they were taken, the external surfaces of the insect and its gut contents have shown a marked similarity. Essentially, the cockroach gut contains precisely the same organisms as are found in its environment.
As with flies, the cockroach gut provides a hospitable and stable environment for the maintenance of pathogens, allowing transmission over a longer period as well as rapid multiplication. Bacteria isolated from the gut of cockroaches include Staphylococcus spp, E. coil, Shigella spp, Salmonella spp.
Cockroaches are extremely mobile animals and their proven ability to crawl from sewers and drains through broken traps into kitchen and hospital environments illustrates their massive potential as spreaders of pathogens. Numerous studies have shown that the incidence of gastro-enteric disease has been curtailed or reduced by control of the cockroach population.
Spread of pathogens by ticks
The increased amount of leisure time enjoyed by members of the public is often spent in pursuits where they may become exposed to ticks. The diseases that ticks carry and the disorders they cause can now come within the scope of the public health pest control professional.
Ticks are not true insects, being more closely related to spiders, mites and scorpions. The tick body is divided into just two sections as opposed to the three sections of the insect body.
For the most part ticks are parasitic, and it is this parasitising of vertebrates, feeding on their blood, that makes them transmitters of disease.
Most ticks are blood sucking parasites at all stages of their life and while the diseases they transmit can be a massive problem, the bites inflicted by them can often cause immense discomfort and some species can induce a general paralysis of the human host.
Ticks can transmit many small microorganisms during their feeding process. It is worth noting that in most cases feeding in ticks is a lengthy process when compared to many of the blood-feeding insects and, therefore, there is ample opportunity for the transference of pathogens.
Some examples are the Rickettsiae, the organisms causing typhus etc; the spirochetes, which may induce many of the relapsing fevers; and many viruses amongst which are the causative agents of various encephalitis-like infections, and finally many bacteria. The bacterial disease spread by ticks, which is increasingly being encountered, is Lyme disease, which is carried by the deer tick. The bacteria can infect dogs, horses, small mammals and humans. Humans can encounter and pick up the deer tick in moorland and on forest walks, hill climbs etc. Lyme disease is easily treatable with antibiotics but the diagnosis is often difficult since initial symptoms are often difficult to spot.