Bed bugs were once a common Public health pest worldwide, which declined in incidence through the mid 20th century. Recently however, bed bugs have undergone a dramatic resurgence and
worldwide there are reports of increasing numbers of infestations. Australia has also been included in this trend and the Department of Medical Entomology,ICPMR, has been at the forefront of documenting this phenomena and providing information on the ecology and control of this important public health pest.
Natural History
Bed bugs are wingless insects, roughly oval in shape, 4-5mm long when fully grown, and are fast runners. They are rust brown in colour and change to a deeper red brown following a blood meal. Bed bugs are dorsoventrally flattened and being thin means that they can hide in narrow cracks and crevices,
making detection often very difficult. The two main species that bite humans include the common bed bug, Cimex lectularius, and the tropical bed bug, Cimex hemipterus. The presence of the former species has been long known in Australia, whereas the tropical bed bug was only recently recognised in the country by the Medical Entomology Department, ICPMR. There are five juvenile stages known as nymphs, which are miniature versions of the adults in
appearance. Each nymphal stage requires at least one blood meal to moult to the next stage and it takes 5-10 minutes for complete engorgement to occur. The entire nymphal development takes 6-8 weeks, while the adult bed bugs can live on average for 6-12 months. All nymphal stages and adults of both sexes require blood for nutrition and development. After mating, each female lays 2-3 eggs a day throughout her lifespan. Thecream coloured eggs (1mm in length) are cemented on rough surfaces of hiding places, and will hatch within around 10 days at room temperature, but longer in
cooler conditions.
The mouthparts of bed bugs are especially adapted for piercing skin and sucking blood. Like most blood sucking arthropods, they inject saliva during feeding, which has anticoagulant properties. Bed bugs respond to the warmth and carbon dioxide of a host and quickly locate a suitable feeding site. They tend not to live on humans and the only contact is for a blood meal. Most blood feeding occurs at night, and they generally seek shelter during the day and become inactive while digesting the blood meal. However, bed bugs are opportunistic and will bite in the day especially if starved for some time. They can survive for long periods without feeding. While their preferred host is human, they will feed on wide variety of other warm-blooded animals including rodents, rabbits, bats, and even birds. Being a cryptic species, bed bugs shelter in a variety of dark locations, mostly close to where people sleep. These include under mattresses, floorboards, paintings and carpets, behind skirting, in various cracks and crevices of walls, within bed frames and other furniture, and behind loose wallpaper. Bed bugs tend to stay in close contact with each other and heavy infestations are accompanied by a distinctive sweet sickly smell. Blood spotting on mattresses and nearby furnishings is often a tell tale sign of an infestation. Bed bugs are one of the great travellers of the world and are readily transported via luggage, clothing, bedding and furniture. As such, they have a worldwide distribution.
Clinical Presentation
Skin reactions are commonly associated with bed bugs, which result from the saliva injected during feeding. Some individuals however, do not react to their bite, whereas others note a great deal of discomfort often with loss of sleep from the persistent biting. The most commonly affected areas of the body are the arms and shoulders. Reactions to the bites may be delayed; up to 9 days before lesions appear. Common allergic reactions
include the development of large wheals, often >1cm, which are accompanied by itching and inflammation. The wheals usually subside to red spots but can last for several days. Bullous eruptions have been reported in association with multiple bed bug bites and anaphylaxis may occur in patients with severe allergies. In India, iron deficiency in infants has been associated with severe infestations. It has been suggested that allergens from bed bugs may be associated with asthmatic reactions. Bed bugs have been implicated in the transmission of a wide variety of infectious agents, although their status as vectors is uncertain. It has been suggested that they might play a role in the spread of hepatitis B, however, experimental evidence does not support this. Note that an irritation or bite experienced in bed may not
necessarily be due to a bed bug infestation.
Feeding Habits
Bedbugs are obligatory hematophagous (bloodsucking) insects. Most species only feed on humans when other prey are unavailable. They are normally out at night just before dawn, with a peak feeding period of about an hour before sunrise,[citation needed] but have been observed feeding during the day.[citation needed] Bedbugs are attracted to their hosts primarily by carbon dioxide, secondarily by warmth, and also by certain chemicals. They reach a detected host by crawling, or sometimes dropping from a height[citation needed]. A bedbug pierces the skin of its host with two hollow feeding tubes. With one tube it injects its saliva, which contains anticoagulants and anesthetics, while with the other it withdraws the blood of its host. After feeding for about five minutes, the bug returns to its hiding place.Although bedbugs can live for a year without feeding, they normally try to feed every five to ten days. When it’s cold, bedbugs can live for about a year; at temperatures more conducive to activity and feeding, about 5 months. At the 57th Annual Meeting of the Entomological Society of America in 2009, it was reported that newer generations of pesticide-resistant bedbugs in Virginia could survive only two months without feeding.
Disease Transmission
Cimicosis is a skin condition caused by bedbug bites. Depending on individual sensitivity, bites can cause a raised red bump or flat welt, sometimes accompanied by very intense itching caused by an allergic reaction to the anesthetic in the bedbug’s saliva.[citation needed] Reactions to bedbug bites may look like mosquito bites, though they tend to last longer.[citation needed] Bites may not be visible and can take up to nine days to appear.[citation needed] Bedbug bites tend not to have a red dot in the center as is characteristic of flea bites.[citation needed] As with flea bites[citation needed], bedbug bites are sometimes sequential, often in rows of three.[citation needed] Individual responses vary greatly. In about 50% of cases,[citation needed] there is no visible sign of bites, greatly increasing the difficulty of identifying and eradicating infestations. This means that itchy welts cannot be used as the only indicator, and that initial infestation can be asymptomatic and go undetected.[citation needed] Serious bed bug infestations and chronic attacks can cause anxiety, stress, and insomnia. Development of refractory delusional parasitosis is possible, as victims develop an overwhelming obsession with bedbugs.Patients given systemic corticosteroids and antihistamines for the itching associated with bites will still have visible signs of bites. Topical corticosteroids, such as hydrocortisone, can reduce lesions and decrease itching. The application of hot water may relieve symptoms. The water temperature should be about 50 °C (120 °F), or this procedure may aggravate the symptoms. Disagreement exists as to why heat causes symptoms to abate. Heat might overwhelm the nerve endings that signal itch; it might neutralize the chemical causing inflammation, or it might trigger a large release of histamine, causing a temporary histamine deficit in the area. Another theory is that the heat denatures the proteins in the bedbug saliva, changing their composition enough so that they no longer trigger the body’s defensive mechanisms.
Laboratory Diagnosis
A bed bug infestation can be diagnosed by the identification of specimens collected from the infected residence. Collection of live or dead bed bugs, cast skins, hatched or unhatched eggs will
determine an infestation. There are two species of bed bug that bloodfeed on humans but Cimex lectularius has the most widespread international distribution; the other species, C. hemipterus, is usually confined to tropical regions.