Public Health Importance

Usinger (1966) listed 27 human pathogens, including viruses, bacteria, protozoa, and helminths, that have been shown to survive for varying lengths of time in C. lectularius and C. hemipterus. However, there is little or no evidence to incriminate bed bugs as vectors of these or any other disease agents.

Recent attempts to explain transmission of hepatitis B virus and, to a lesser extent, HIV in otherwise unexplained situations have focused on the possibility of cimi-cid transmission. Hepatitis B antigens survive in cimicid tissues and feces under laboratory conditions; however, attempts to transmit the virus from infected bugs to chimpanzees failed. These results and those from transmission studies with mosquitoes suggest that it is unlikely that hepatitis B transmission occurs via either infective feces or interrupted feedings.

Although transmission studies with bed bugs and HIV indicate that these insects may harbor the virus for up to 8 days, replication of the virus does not occur and the virus is not present in cimicid feces. These observations, together with failed attempts to experimentally transmit HIV by interrupted feedings, suggest that cimicids are neither biological nor mechanical vectors of HIV.

Despite the fact that cimicids do not play a significant role as vectors of human pathogens, bed bugs are medically important because they cause unpleasant bite reactions and significant blood loss in people living in dwellings that are chronically infested. The actual feeding by bed bugs generally does not produce any pain. If interrupted, a bug will often bite again close to the previous site, thereby creating a linear array of punctures that is characteristic of cimicid bites. People are most often bitten on the limbs, trunk, and face.

Sensitivity reactions to bed bug bites are the result of substances injected during feeding. These reactions may be localized cutaneous responses, or they may be generalized and systemic. The most common local reactions are wheals similar to uncomplicated mosquito bites or, in some individuals, large fluid-filled bullae. Erythema is not a common response but may occur as a result of multiple feedings that cause extensive hemorrhaging under the skin. Individual reactions to cimicid bites vary from no response to severe immediate or delayed sensitivity reactions, including anaphylaxis. In most cases, swelling and itching associated with the bites can be relieved by application of ice and use of an oral antihistamine. Chronic bed bug bites are sometimes misdiagnosed as allergic dermatitis or other skin disorders. Accurate clinical assessment often requires careful epidemiological evaluation of a patient's living quarters.

People living with chronic infestations of bed bugs often are subject to nightly attacks, resulting in a marked loss of blood and associated iron deficiency. Children who are marginally nourished are especially vulnerable to developing anemia and other medical problems as a result of such chronic blood loss. Individuals subjected to continued feeding by bed bugs may also develop extreme irritability that results from restless nights and chronic sleep deprivation. If the source of the disturbance goes undetected, the emotional stress caused by such infestations may be misdiagnosed as a neurosis.

In addition to the three cimicid species directly associated with human habitations, there are several species that occasionally feed on people. These include swallow bugs of the genus Oeciacus; the bat bugs C. pilosellus(New World) and C. pipistrelli (Europe); and the bird bugs, such as the

Other Cimicids Which Occasionally Attack Humans

Mexican chicken bug Haematosiphon inodorus andCimex-opsis nyctalis from the nests of chimney swifts. Human bites by these species generally occur only in the vicinity of the nesting or roosting sites of their natural hosts.

The swallow bugs that occur in mud nests of swallows include two species: Oeciacus birundinisin Eurasia south to Morocco and O. vicarius in North America south to Durango in Mexico. Both species are members of the subfamily Cimicinae and will bite people who disturb infested bird nests. Swallows may be heavily infested with the bugs, and nestlings often die as a result of blood loss. The eggs of Oeciacusspecies are attached to the outer surfaces of swallow mud nests, often being so abundant that they can be seen from a distance. There is some evidence that Oeciacus species are carried as nymphs by the birds from nest to nest.

An arbovirus has been isolated from the cliff swallow bug O. vicarius, nestling cliff swallows, and house sparrows in eastern Colorado. This is an alphavirus> part of the western equine encephalitis complex called Fort Morgan virus. It is not known to cause pathology in its avian hosts or in humans. Occurrence of this virus in bugs and birds suggests that viruses can overwinter in swallow bugs that occupy nests left vacant by their migrating hosts.

Cimicids can be significant pests in commercial poultry production. Cimicids attacking domestic poultry include Cimex kctularius 'm North America, Europe, and the former Soviet Union; H. inodorus in Central America; and Ornithocoris tolsdoi in Brazil.

Raised slats and wood shavings in nest boxes in broiler breeder houses provide harborage for the bugs. Indications of cimicid infestations include fecal spots on eggs, nest boxes (Fig. 5.14), and wooden supports, skin lesions on the breasts and legs of birds, reduced egg production, and increased consumption of feed. Chicken bugs are not known to transmit any avian pathogens. However, chickens and other fowl raised in poultry houses heavily infested with chicken bugs are irritable and often anemic. Morbidity in such cases may be high, and young birds may succumb from blood loss.

Two species of nonpathogenic trypanosomes which undergo development in cimicids have been isolated from bats in North America. Trypanosoma hedrickizn√° T. my-oti, both closely related to T. cruzi, have been found in big brown bats and little brown bats in southern Ontario, Canada. Developmental stages infective to bats form in the rectum of C. brevis and C. lectularius, which suggests that these trypanosomes are transmitted by the

Black Fly Public Health Important
FIGURE 5.14 Fecal spots, indicative of cimicid activity, along scams of nesting boxes of laying hens in a poultry house heavily infested with Cimex lectularius. (Photo by G. R. Mullen)

bugs via the posterior-station route. Because bats also are known hosts for T. cruzi, the differentiation of other bat trypanosomes and the elucidation of their transmission are important. Furthermore, because of the similarities of the life cycles and transmission of these nonpathogenic trypanosomes to those of T. cruzi, they could be suitable candidates for developing laboratory models of the Chagas disease pathogen.

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Oplan Bed Bugs

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