Cockroaches are among the oldest surviving insect forms on the planet, and they have diversified extensively in the last 300 million years. They are thought to be associated with human populations since the time of cave dwellers , but they predate humans by more than 300 million years to the geologic age known as the Carboniferous period in the late Paleozoic era. Nevertheless, modern families of cockroaches date back to Mesozoic period , some 150 million years ago. So far about 4,500 species have been identifies and described. in 515 genera, and scientists believe there are more than 5,000 species that remain undiscovered or unnamed.
Cockroaches belong to the order Blattaria, from the Greek word blattae. While the Greeks called cockroaches blats , the Romans referred to them as lucifuga for their habit of avoiding and fleeing from light, the word cockroach did not come into usage until much later. The term cockroach can be traced to the Spanish cucaracha , where it was used by a Spanish playwright in the mid-1500s.
The American cockroach despite its name, was introduced on ships directly from Africa, while the origin of the German cockroach is less certain. Some believe that it originated in East Africa and others state it comes from Southeast Asia.
Whatever the origin, cockroaches are used by humans in myriad of ways. A number of large , slow moving tropical species – most commonly the Madagascar hissing cockroach – have become popular pets sold in pet shops and by increasing number of internet vendors. Cockroaches are also sold as “feeders” for other invertebrates, reptiles, and amphibians , and as collectors’ items in ever growing market of hobbyists who raise, breed, and exchange cockroaches.
Public Health Significance of Cockroaches
Cockroaches are considered pests of public health importance because they are closely associated with humans and and commonly freed and feed in unsanitary areas such as garbage storage, sewer systems, and septic tanks.. The German and American cockroaches, especially , are usually the most prominent and therefore most important of the household cockroaches.
A survey of public housing residents reported that more than 75% of tenants considered cockroach a serious problem; when asked what people disliked most about cockroaches , some residents reported that “having them was a source of embarrassment” , and others expressed health – related concerns. Most importantly, however, in recent years, cockroaches have emerged as a major source of allergens and major cause of asthma morbidity
Cockroaches as a source of Allergens and Asthma Triggers
For nearly half a century, cockroaches have been recognized as a major cause of asthma morbidity in the urban, inner-city environment . Although successful removal of cockroach allergens ( fecal matter ) from the infested environment has been difficult to accomplish with remedial sanitation, large scale reduction in cockroach allergens below clinically relevant thresholds have recently been attained through elimination of cockroach population.Asthma is a multifaceted , chronic lung disease characterized by bronchial inflammation that leads to recurrent episodes of breathlessness, wheeze, cough, tightness or pain in the chest. In the U.S. , asthma affects over 30 million people and is one of the most costly diseases, estimated at $12.7 billion in 1998. It is the most frequent cause of hospitalization among children. The prevalence of asthma has increased dramatically over the past 40 years, mainly as a consequence of changes in housing design and more time spent indoors, resulting in a prolonged exposure to allergens. About 26% of U.S. population is sensitive to German cockroach allergen by skin test, the highest of all cockroaches. The most commonly measured allergens in environment in intervention studies are Bla g1 and Bla g2 ( both from German cockroach) both of which are produced in the cockroach gut and excreted in feces.Further studies show that inner city youth, Hispanics and African Americans are 12 times more likely to become sensitive to cockroach allergens. The main cause for this relationship is the socioeconomic status of these two groups relative to Caucasian population. Hispanic and African American children are more likely than Caucasian children to live in a multi-unit apartment buildings which are considered more conducive for cockroach infestation. The most sensitization occurs by inhalation of airborne allergens Bla g 1 and Bla g2 are carried principally by dust particles with diameter greater than 10 Micrormeter and remain airborn for about 30 minutes after disturbance.
Cockroach Allergen Control and Elimination
A clear correlation between the size of an infestation and the concentration of the allergen Bla g1 suggests that failure to reduce allergen might be related to unsatisfactory cockroach control. Most cockroach allergen mitigations have used a mix of intervention strategies, most commonly pest control coupled with cleaning, but, in most cases , allergen reductions have been short-lived and allergens subsequently increased. Most such studies assumed that pest control was effective , but without monitoring the cockroach population. Numerous studies and field research show that only a complete program based on combination of education, cleaning, and targeted bait based insecticide pest control programs produced very high or total allergen reduction. Yet again, the intensive , targeted approach was highly effective , reducing cockroach populations by 97% withing 6 months. These data show , however, that the pest management service was substantially less effective at reducing cockroach infestations ( 53% reduction after 6 months ), but comparable to most of the previous intensive environmental interventions that employed commercial service and reported trap catches. These studies underscore that while professional pest control is a pivotal strategy in allergen mitigation, the specific tactics employed to suppress cockroach population will significantly impact cockroach control and consequently the level of environmental allergens.
These findings suggest that the disparity between the efficacy of pest professionals and professional entomologists is likely the use of residual spray by the former group and baits and integrated pest management (IPM) approaches by the latter. These ideas are consistent with findings that scheduled residual insecticide treatments ( spraying ) often have little effect on cockroach population in multi-unit housing.
Cockroaches as Vectors of Human Pathogens
The potential for mechanical transmission of pathogenic organisms by cockroaches is exacerbated by their free movement between waste and food, where cockroaches can acquire, carry, and disseminate pathogenic bacteria, parasitic worms, fungi, protozoa, and viruses either externally or in their digestive system. Many pathogenic organisms have been isolated from cockroaches collected in and around human environments , including the pathogenic bacteria responsible for bubonic plague, dysentery, diarrhea, urinary track infection, abscesses, food poisoning, gastroenteritis, typhoid fever, leprosy and nocardiosis. Unlike many blood feeding arthropods whose feeding feeding behavior results in a direct transmission of pathogens to humans, cockroaches have the potential to transmit pathogens mechanically via contamination of foods or utensils used to prepare food. Surprisingly, a recent survey found that cockroaches carry more species of pathogenic bacteria than house flies.