Hematophagy is a behavior of feeding on blood taken from vertebrate hosts. It is practiced by about 15,000 species and about 400 genera of arthropods (Mans, Louw et al. 2002). It has also been reported that blood-feeding has evolved independently at least six times. In addition to arthropods, members of other phyla including annelids such as worms and leeches are hematophagous. While independent evolution and wide-spread occurrence of taking blood-meals have resulted in considerable biological diversity, there are consistent characteristics pertinent to strategies for hematophagy including: locating and accessing a suitable blood-containing host, penetrating the integument and blood circulatory system, counteracting the hemostatic system of the host, taking a blood-meal and escaping detection so as to survive to digest the meal.
To obtain blood, hematophagous ectoparasites cut or pierce the epithelium and disrupt the integrity of the circulatory system of the host. During this process of gaining access to blood and feeding on blood, hematophages may inject substances into the host such substances being brought to the symbiotic relationship by the parasite. These injected substances may be either produced by the parasite and assist in blood-feeding or present in the hematophage as a residue of previous feeding.
Blood-feeding behavior results in numerous new infections in humans per year and many more in animals. Among the most widely known of these infections are cases of malaria resulting from mosquito bites. While Yellow fever, Chagas disease, Dengue fever, Ebola, and other diseases are transmitted by tropical insects, human arthropod-borne infections also occur in non-tropical regions. Infectious diseases such as Borrelia, Babesia, Rickettsia, West Nile virus, and various types of encephalitis infections are found in cold weather climates in the Northern Hemisphere. Similarly, many non-human species are infected by hematophagous parasites and may serve as alternate hosts or reservoirs for human pathogens.
Among blood-feeding organisms, arthropods are possibly the best known. Included in this group are arachnids (ticks and mites) and insects, flies, bugs, and lice. Some hematophagous parasites require blood-meals at every stage of life, such as is the case with ticks, lice, and bedbugs, and others only as adults and in some cases only females are parasitic. Some hematophages spend their entire life on the hosts such as is the case with head lice. Other species, such as bedbugs, get onto the source of blood only to feed. The wide biological diversity of hematophagous organisms presents a challenge to detecting and controlling these pests.
Sources of blood for these parasites are vertebrates including, most importantly, terrestrial reptiles, birds, and mammals because of their association with humans. Some species of hematophages are opportunistic and will take meals from a variety of host species whereas others may preferentially or obligately feed on one host species. In many cases humans are more exposed to hematophagous organisms upon leaving shelter. Well-known blood-sucking insects, such as mosquitoes and biting flies, and ticks, live primarily outdoors. While these parasites may enter houses, primarily to feed, they usually do not infest human shelters. Typically, arthropod life cycles are more compatible with the environment outside of human dwellings and humans are opportunistically used as sources of blood.
There are, however, animals that opportunistically share houses with humans even in developed countries. These organisms are commonly known as pests. Many arthropod pests enter a dwelling with other pests; for example, fleas may come in on rodents. It is also possible that pests enter dwellings on their own, with the humans themselves, or companion animals such as dogs or cats carry pests into the homes. Infestations by hematophagous ectoparasites can cause annoyance, discomfort, health problems, and economic losses. For example, pests in structures other than those for human habitation, including but not limited to hen houses for avian egg production, barns housing domestic animals, mammalian breeding facilities, or other structures for continued occupation by birds or mammals, may cause reduced productivity. Once inside, some arthropods are able to establish breeding colonies in the home. Often the homeowner is not aware of such infestations. For example, house dust mite colonies exist in a high percentage of homes in the United States without the human co-inhabitants being aware of their presence. These organisms feed primarily on human skin flakes that are sloughed constantly and are a component of house dust. House dust can also serve as the main nutrient source for immature fleas, obligate blood-feeders as egg producing adults.
Pesticide use to control many hematophagous species has undergone significant changes with the virtual elimination of “residual insecticides” (Spielman, Pollack et al. 2001). Subsequently, current pest management practices have not eliminated hematophagous ectoparasites from shelters: school children still are infected by head lice (Pediculus capitas); bedbugs (Cimex lectularius) infest henhouses and are being found with increasing frequency in homes and lodging facilities in the United States; fleas (Ctenocephalides sp.) and several genera of ticks enter structures inhabited by humans, mice, dogs, cats, and other mammals alone or in combination; and companion animals of humans are frequently hosts for are variety arachnid and insect ectoparasites. Because modern integrated pest management practices tend toward more judicious use of pesticides, determining that an infestation exists is a necessary first step in controlling pests and is useful in evaluating the effectiveness of control measures taken. Currently visual inspection either directly or using various collection and magnification aids is the primary means to determine the presence of pests. Frequent publication of articles and patents describing new and better ways to detect the presence of pests attests to the fact that current methods need improvement.
As mentioned above, blood-sucking parasites may inject substances into the host during feeding. Compounds of parasite origin have been found to have various physiological activities including anticoagulation, platelet aggregation inhibition, pain inhibition, and anti-inflammation. Such findings have lead to published studies describing the structure and function of these compounds of possible use as pharmaceuticals. Hirudin, produced by the leech Hirudo medicinalis, has been cloned for mass production by recombinant DNA technology and is available for treating humans as “Refludan” (BERLEX Laboratories, Wayne, N.J.). This and other therapeutic applications have lead to an expanding literature base in pharmacognosy focused on proteins, especially of salivary origin, elaborated by hematophagous invertebrates to assist in blood-feeding (Valenzuela, Walker et al. 1995; Valenzuela, Charlab et al. 1998; Valenzuela, Belkaid et al. 2001). These studies have provided DNA sequences for many salivary proteins which served as useful prior art for the present invention. Salivary biomolecules are injected into the host circulatory system where the physiological effects occur. The proteins of hematophage origin are also carried by the blood into the parasite digestive system where they become part of the blood-meal and are subject to degradation by the digestive hydrolytic processes. As a result, the structure and molecular characteristics of salivary proteins may be altered during passage through the digestive system of parasites and be different from those of the salivary proteins per se or produced from recombinant genes.
Vertebrate blood is typically about 80% water. Many hematophagous invertebrates, especially ectoparasitic species, utilize diuresis mechanisms to eliminate much of the water from a blood-meal very quickly usually as feces (Quinlan, Tublitz et al. 1997). This is necessary for many reasons including improved mobility of the pest to avoid being detected and preyed upon or swatted and more efficient digestion. The very liquid feces contain compounds that have undergone little digestion during the short time between feeding and excretion. These feces will contain biomolecular markers of blood feeding activity derived from both the host blood and those associated with the hematophagous organism involved.
Various types of tests have proven to be reliable and cost-effective for detecting biomolecules. Those skilled in the art of detecting molecules of biological origin have developed various methods to offer rapid, easy-to-use, and specific tests with sufficient sensitivity to be useful for detecting markers for a wide variety of organisms including but not limited to bacteria, viruses, parasites, and arthropods in the environment. Many of these assays take advantage of the chemical composition and of specific binding properties of biochemicals including but not limited to effectors, inhibitors, modulators, and hormones binding with receptors; lipids, metals, proteins, hormones being specifically bound to carrier proteins; antibodies binding to cell surface binding domains; and the well-know interaction between antigens and antibodies. Thus, while detection assays are know in the art, such assays have not been successfully adapted to the detection of hematophagous ectoparasites that live outside of the body of the host by the methods and compositions of this invention.