Insects and the Transmission of Bacterial Agents.

Arthropods are small invertebrate animals, among which some species are hematophagous. It is during their blood meal that they can transmit pathogenic microorganisms that they may be harboring to the vertebrate host that they parasitize, which in turn will potentially develop a vector-borne disease. The transmission may occur directly through their bite, but also through contaminated feces. Zoonotic diseases, diseases that can naturally be transmitted between humans and animals, are a considerable part of emerging diseases worldwide, and a major part of them are vector-borne. Research and public attention has long been focused on malaria and mosquito-borne arboviruses, and bacterial vector-borne diseases remains today a neglected field of medical entomology. Despite the emphasis on Lyme disease in recent decades, and despite the major outbreaks caused by bacteria in the last few centuries, this field has in fact been poorly explored and is therefore relatively poorly known, other than the most famous examples such as the plague and epidemic typhus outbreaks. Here we propose to review the state of knowledge of bacterial agents transmitted by arthropod vectors.

Rickettsia australis and Queensland Tick Typhus: A Rickettsial Spotted Fever Group Infection in Australia.

Rickettsia australis, the etiologic agent of Queensland tick typhus (QTT), is increasingly being recognized as a cause of community-acquired acute febrile illness in eastern Australia. Changing human population demographics, climate change, and increased understanding of expanding vector distribution indicate QTT is an emerging public health threat. This review summarizes the epidemiology, pathogenesis, clinical features, treatment principles, and future directions of this disease. Increased recognition of QTT will enable consideration of and prompt treatment of R. australis infection by clinicians in Australia.

A Mixed Outbreak of Epidemic Typhus Fever and Trench Fever in a Youth Rehabilitation Center: Risk Factors for Illness from a Case-Control Study, Rwanda, 2012.

In August 2012, laboratory tests confirmed a mixed outbreak of epidemic typhus fever and trench fever in a male youth rehabilitation center in western Rwanda. Seventy-six suspected cases and 118 controls were enrolled into an unmatched case-control study to identify risk factors for symptomatic illness during the outbreak. A suspected case was fever or history of fever, from April 2012, in a resident of the rehabilitation center. In total, 199 suspected cases from a population of 1,910 male youth (attack rate = 10.4%) with seven deaths (case fatality rate = 3.5%) were reported. After multivariate analysis, history of seeing lice in clothing (adjusted odds ratio [aOR] = 2.6, 95% confidence interval [CI] = 1.1-5.8), delayed (≥ 2 days) washing of clothing (aOR = 4.0, 95% CI = 1.6-9.6), and delayed (≥ 1 month) washing of beddings (aOR = 4.6, 95% CI = 2.0-11) were associated with illness, whereas having stayed in the rehabilitation camp for ≥ 6 months was protective (aOR = 0.20, 95% CI = 0.10-0.40). Stronger surveillance and improvements in hygiene could prevent future outbreaks.

Human louse-transmitted infectious diseases.

Several of the infectious diseases associated with human lice are life-threatening, including epidemic typhus, relapsing fever, and trench fever, which are caused by Rickettsia prowazekii, Borrelia recurrentis, and Bartonella quintana, respectively. Although these diseases have been known for several centuries, they remain a major public health concern in populations living in poor-hygiene conditions because of war, social disruption, severe poverty, or gaps in public health management. Poor-hygiene conditions favour a higher prevalence of body lice, which are the main vectors for these diseases. Trench fever has been reported in both developing and developed countries in populations living in poor conditions, such as homeless individuals. In contrast, outbreaks of epidemic typhus and epidemic relapsing fever have occurred in jails and refugee camps in developing countries. However, reports of a significantly high seroprevalence for epidemic typhus and epidemic relapsing fever in the homeless populations of developed countries suggest that these populations remain at high risk for outbreaks of these diseases. Additionally, experimental laboratory studies have demonstrated that the body louse can transmit other emerging or re-emerging pathogens, such as Acinetobacter baumannii and Yersinia pestis. Therefore, a strict survey of louse-borne diseases and the implementation of efficient delousing strategies in these populations should be public health priorities.

Evidence of a louse-borne outbreak involving typhus in Douai, 1710-1712 during the war of Spanish succession.

BACKGROUND: The new field of paleomicrobiology allows past outbreaks to be identified by testing dental pulp of human remains with PCR. METHODS: We identified a mass grave in Douai, France dating from the early XVIII(th) century. This city was besieged during the European war of Spanish succession. We tested dental pulp from 1192 teeth (including 40 from Douai) by quantitative PCR (qPCR) for R. prowazekii and B. quintana. We also used ultra-sensitive suicide PCR to detect R. prowazekii and genotyped positive samples. RESULTS AND DISCUSSION: In the Douai remains, we identified one case of B. quintana infection (by qPCR) and R. prowazekii (by suicide PCR) in 6/21 individuals (29%). The R. prowazekii was genotype B, a genotype previously found in a Spanish isolate obtained in the first part of the XX(th) century. CONCLUSION: Louse-borne outbreaks were raging during the XVIII(th) century; our results support the hypothesis that typhus was imported into Europe by Spanish soldiers from America.

The plague of Athens: epidemiology and paleopathology.

In 430 BC, a plague struck the city of Athens, which was then under siege by Sparta during the Peloponnesian War (431-404 BC). In the next 3 years, most of the population was infected, and perhaps as many as 75,000 to 100,000 people, 25% of the city's population, died. The Athenian general and historian Thucydides left an eye-witness account of this plague and a detailed description to allow future generations to identify the disease should it break out again. Because of the importance of Thucydides and Athens in Western history and culture, the Plague of Athens has taken a prominent position in the history of the West for the past 2500 years. Despite Thucydides' careful description, in the past 100 years, scholars and physicians have disagreed about the identification of the disease. Based on clinical symptoms, 2 diagnoses have dominated the modern literature on the Athenian plague: smallpox and typhus. New methodologies, including forensic anthropology, demography, epidemiology, and paleopathogy, including DNA analysis, have shed new light on the problem. Mathematical modeling has allowed the examination of the infection and attack rates and the determination of how long it takes a disease to spread in a city and how long it remains endemic. The highly contagious epidemic exhibited a pustular rash, high fever, and diarrhea. Originating in Ethiopia, it spread throughout the Mediterranean. It spared no segment of the population, including the statesman Pericles. The epidemic broke in early May 430 BC, with another wave in the summer of 428 BC and in the winter of 427-426 BC, and lasted 4.5 to 5 years. Thucydides portrays a virgin soil epidemic with a high attack rate and an unvarying course in persons of different ages, sexes, and nationalities.The epidemiological analysis excludes common source diseases and most respiratory diseases. The plague can be limited to either a reservoir diseases (zoonotic or vector-borne) or one of the respiratory diseases associated with an unusual means of persistence, either environmental/fomite persistence or adaptation to indolent transmission among dispersed rural populations. The first category includes typhus, arboviral diseases, and plague, and the second category includes smallpox. Both measles and explosive streptococcal disease appear to be much less likely candidates.In 2001, a mass grave was discovered that belonged to the plague years. Ancient microbial typhoid (Salmonella enterica serovar Typhi) DNA was extracted from 3 skeletons. Because typhoid was endemic in the Greek world, it is not the likely cause of this sudden epidemic. Mt Sinai J Med 76:456-467, 2009. (c) 2009 Mount Sinai School of Medicine.

Cluster of sylvatic epidemic typhus cases associated with flying squirrels, 2004-2006.

In February 2006, a diagnosis of sylvatic epidemic typhus in a counselor at a wilderness camp in Pennsylvania prompted a retrospective investigation. From January 2004 through January 2006, 3 more cases were identified. All had been counselors at the camp and had experienced febrile illness with myalgia, chills, and sweats; 2 had been hospitalized. All patients had slept in the same cabin and reported having seen and heard flying squirrels inside the wall adjacent to their bed. Serum from each patient had evidence of infection with Rickettsia prowazekii. Analysis of blood and tissue from 14 southern flying squirrels trapped in the woodlands around the cabin indicated that 71% were infected with R. prowazekii. Education and control measures to exclude flying squirrels from housing are essential to reduce the likelihood of sylvatic epidemic typhus.

Epidemic typhus.

Epidemic typhus is transmitted to human beings by the body louse Pediculus humanus corporis. The disease is still considered a major threat by public-health authorities, despite the efficacy of antibiotics, because poor sanitary conditions are conducive to louse proliferation. Until recently, Rickettsia prowazekii, the causal agent, was thought to be confined to human beings and their body lice. Since 1975, R prowazekii infection in human beings has been related to contact with the flying squirrel Glaucomys volans in the USA. Moreover, Brill-Zinsser disease, a relapsed form of epidemic typhus that appears as sporadic cases many years after the initial infection, is unrelated to louse infestation. Stress or a waning immune system are likely to reactivate this earlier persistent infection, which could be the source of new epidemics when conditions facilitate louse infestation. Finally, R prowazekii is a potential category B bioterrorism agent, because it is stable in dried louse faeces and can be transmitted through aerosols. An increased understanding of the pathogenesis of epidemic typhus may be useful for protection against this bacterial threat.

Survey for zoonotic rickettsial pathogens in northern flying squirrels, Glaucomys sabrinus, in California.

Epidemic typhus, caused by Rickettsia prowazekii, is maintained in a southern flying squirrel (Glaucomys volans) sylvatic cycle in the southeastern United States. The northern flying squirrel (Glaucomys sabrinus) has not been previously associated with R. prowazekii transmission. A second rickettsial pathogen, Anaplasma phagocytophilum, infects dusky-footed woodrats (Neotoma fuscipes) and tree squirrels in northern California. Because northern flying squirrels or their ectoparasites have not been tested for these rickettsial pathogens, serology and polymerase chain reaction (PCR) were used to test 24 northern flying squirrels for R. prowazekii and A. phagocytophilum infection or antibodies. Although there was no evidence of exposure to R. prowazekii, we provide molecular evidence of A. phagocytophilum infection in one flying squirrel; two flying squirrels also were seropositive for this pathogen. Fleas and ticks removed from the squirrels included Ceratophyllus ciliatus mononis, Opisodasys vesperalis, Ixodes hearlei, Ixodes pacificus, and Dermacentor paramapertus.

Pathogenic rickettsiae as bioterrorism agents.

Because of their unique biological characteristics, such as environmental stability, small size, aerosol transmission, persistence in infected hosts, low infectious dose, and high associated morbidity and mortality, Rickettsia prowazekii and Coxiella burnetii have been weaponized. These biological attributes would make the pathogenic rickettsiae desirable bioterrorism agents. However, production of highly purified, virulent, weapon-quality rickettsiae is a daunting task that requires expertise and elaborate, state-of-the art laboratory procedures to retain rickettsial survival and virulence. Another drawback to developing rickettsial pathogens as biological weapons is their lack of direct transmission from host to host and the availability of very effective therapeutic countermeasures against these obligate intracellular bacteria.

Arthropod-borne diseases in homeless.

Homeless people are particularly exposed to ectoparasite. The living conditions and the crowded shelters provide ideal conditions for the spread of lice, fleas, ticks, and mites. Body lice have long been recognized as human parasites and although typically prevalent in rural communities in upland areas of countries close to the equator, it is now increasingly encountered in developed countries especially in homeless people or inner city economically deprived population. Fleas are widespread but are not adapted to a specific host and may occasionally bite humans. Most common fleas that parasite humans are the cat, the rat, and the human fleas, Ctenocephalides felis, Xenopsylla cheopis, and Pulex irritans, respectively. Ticks belonging to the family Ixodidae, in particular, the genera Dermacentor, Rhipicephalus, and Ixodes, are frequent parasites in humans. Sarcoptes scabiei var. hominis is a mite (Arachnida class) responsible for scabies. It is an obligate parasite of human skin. The hematophagic-biting mite, Liponyssoides sanguineus, is a mite of the rat, mouse, and other domestic rodents but can also bite humans. Finally, the incidence of skin disease secondary to infestation with the human bedbug, Cimex lectularius, has increased recently. Bacteria, such as Wolbacchia spp. have been detected in bedbug. The threat posed by the ectoparasite in homeless is not the ectoparasite themselves but the associated infectious diseases that they may transmit to humans. Except for scabies all these ectoparasites are potential vectors for infectious agents. Three louse-borne diseases are known at this time. Trench fever caused by Bartonella quintana (B. quintana), epidemic typhus caused by Rickettsia prowazekii, and relapsing fever caused by the spirochete Borrelia recurrentis. Fleas transmit plague (Xenopsylla cheopis and Pulex irritans), murine typhus (Xenopsylla cheopis), flea-borne spotted rickettsiosis on account of the recently described species Rickettsia felis (C. felis), and occasionally cat scratch disease on account of Bartonella henselae (C. felis). The role of fleas as potential vector of B. quintana has recently been suggested. Among the hematophagic-biting mites, L. sanguineus, is responsible for the transmission of Rickettsia akari, the etiologic agent of rickettsialpox. Virtually, no data are available on tick-borne disease in this population. This article will deal with epidemiology, diagnosis, prevention, and treatment of these ectoparasite and the infectious diseases they transmit to the homeless people.

A stranger to our camps: Typhus in American history.

Medical observers during the American Civil War were happily surprised to find that typhus fever rarely made an appearance, and was not a major killer in the prisoner-of-war camps where the crowded, filthy, and malnourished populations appeared to offer an ideal breeding ground for the disease. Through a review of apparent typhus outbreaks in America north of the Mexican border, this article argues that typhus fever rarely if ever extended to the established populations of the United States, even when imported on immigrant ships into densely populated and unsanitary slums. It suggests that something in the American environment was inhospitable to the extensive spread of the disease, most likely an unrecognized difference in the North American louse population compared to that of Europe.

Eradication of typhus exanthematicus in Bosnia and Herzegovina.

Typhus exanthematicus in Bosnia and Herzegovina held in endemic areas from which especially quickly began spread after 1945. That year, in 1945, one hundred epidemics of typhus fever appeared, with the highest incidence rate in Europe of 215.04 per 1,000. Directions of unique program in the world were to eradicate lice of the body, but also establish monitoring of the recidivism, Brill-Zinsser disease. Since 1971, typhus exanthematicus (classical typhus) hasn't appeared in Bosnia and Herzegovina, so epidemic typhus can considered as an eradicated communicable disease.

[Lice and lice-borne diseases in humans]. / Les poux et les maladies transmises á l'homme.

Among the three lice which parasite the human being, the human body louse, Pediculus humanus humanus, is a vector of infectious diseases. It lives and multiplies in clothes and human infestation is associated with cold weather and a lack of hygiene. Three pathogenic bacteria are transmitted by the body louse: 1) Rickettsia prowazekii, the agent of epidemic typhus of which the most recent outbreak (and the largest since World War II) was observed during the civil war in Burundi; 2) Borrelia recurrentis, the agent of relapsing fever, historically responsible of massive outbreaks in Eurasia and Africa, which prevails currently in Ethiopia and neighboring countries; 3) Bartonella quintana, the agent of trench fever, bacillary angiomatosis, chronic bacteremia, endocarditis, and lymphadenopathy. Body louse infestation, associated with a decline in social and hygienic conditions provoked by civil unrest and economic instability, is reemergent worldwide. Recently, a forth human pathogen, Acinetobacter baumannii, has been associated to the body louse.