New molecular biology detection methods for tick-borne infectious agents

Tick-borne zoonotic pathogens are well known in many areas all over the world. Among the tick-borne transmitted diseases in Switzerland, Lyme disease caused by Borrelia burgdorferi, ehrlichiosis caused by various species of Ehrlichia and tick-borne encephalitis caused by the tick-borne encephalitis virus (TBEV) are the most important zoonotic diseases. Early diagnosis and treatment is necessary to prevent fatal infections and chronic damage to various tissues. Due to the variety of uncharacteristic clinical signs, tick-borne diseases are not easily recognized. Diagnosis is based on clinical findings, a record of tick exposure, and direct or indirect detection of the pathogen. Here we discuss briefly the most important tick-borne infections and their diagnosis with emphasis on a new molecular diagnostic tool--the real-time TaqMan PCR--and its importance for the diagnosis of tick-borne pathogens.     

Tick-borne zoonoses: Lyme disease, ehrlichiosis, and Rocky Mountain spotted fever

The primary health risk for veterinary staff and companion pet owners is exposure to ticks in the wooded/pasture areas or to ticks brought indoors by their pets. There are no proven cases of direct animal to human transmission for Lyme disease, ehrlichiosis, or Rocky Mountain spotted fever. Direct inoculation of blood from a bacteremic animal, eg, by needle stick is a theoretical, but, so far, undocumented health risk. However, veterinarians should record needle sticks or other inoculation-type injuries that occur in their practices. Prevention of Lyme disease, ehrlichiosis, Rocky Mountain spotted fever, and other tick-borne diseases depends on the avoidance of tick-infested areas and proper use of repellents and acaricides.     

Review of diagnostic plaque reduction neutralization tests for flavivirus infection

Flavivirus infections (including Japanese encephalitis, West Nile encephalitis and dengue fever/severe dengue) present a worldwide public health problem. Recent climate change may affect the geographical distribution of the arthropod vectors for these viruses and so the risk of flavivirus epidemics may increase. Many methods have been developed for the serological diagnosis of flavivirus infections, such as haemagglutination inhibition assay, enzyme-linked immunosorbent assay, and immunofluorescence in staining. However, the specificity of these assays varies.The plaque reduction neutralizing test (PRNT) using live viruses is currently the ‘gold standard’ for the differential serodiagnosis of flaviviruses. The specificity of results obtained with PRNT is better than that for other protocols and many laboratories apply the PRNT protocol to the differential serodiagnosis of flaviviruses. Here, recent refinements to the PRNT protocols with genetically modified recombinant viruses or reporter-harbouring virus-like particles are reviewed. Further, the problems associated with the differential serodiagnosis of flaviviruses using PRNT are discussed.     

Ganjam virus/Nairobi sheep disease virus induces a pro-inflammatory response in infected sheep

Partly due to climate change, and partly due to changes of human habitat occupation, the impact of tick-borne viruses is increasing. Nairobi sheep disease virus (NSDV) and Ganjam virus (GV) are two names for the same virus, which causes disease in sheep and goats and is currently known to be circulating in India and East Africa. The virus is transmitted by ixodid ticks and causes a severe hemorrhagic disease. We have developed a real-time PCR assay for the virus genome and validated it in a pilot study of the pathogenicity induced by two different isolates of NSDV/GV. One isolate was highly adapted to tissue culture, grew in most cell lines tested, and was essentially apathogenic in sheep. The second isolate appeared to be poorly adapted to cell culture and retained pathogenicity in sheep. The real-time PCR assay for virus easily detected 4 copies or less of the viral genome, and allowed a quantitative measure of the virus in whole blood. Measurement of the changes in cytokine mRNAs showed similar changes to those observed in humans infected by the closely related virus Crimean Congo hemorrhagic fever virus.     

Tick-borne fever: A review

The literature on tick-borne fever is reviewed. Tick-borne fever is a rickettsial disease of sheep and cattle characterised by high fever and severe leucopaenia. The causative agent,Cytoecetes phagocytophila invades the neutrophils and monocytes and is transmitted by the tickIxodes ricinus. There is very little information on the pathogenesis and immunogenesis of the disease but there is ample evidence that infected animals are predisposed to other diseases. Animals infected with tick-borne fever resist reinfection for a variable period of time. The organisms may persist in the blood of recovered animals for up to two years. Humoral antibodies are produced two weeks after infection and continue to be detected for many months but their significance on protective immunity is not clearly established.     

Epizootiological study of tick-borne encephalitis virus infection in Japan

Tick-borne encephalitis virus (TBEV) is a zoonotic agent causing severe encephalitis in humans. Rodent species that are potential hosts for TBEV are widely distributed in various regions in Japan. In this study, we carried out large-scale epizootiological surveys in rodents from various areas of Japan. A total of 931 rodent and insectivore sera were collected from field surveys. Rodents seropositive for TBEV were found in Shimane Prefecture in Honshu and in several areas of Hokkaido Prefecture. These results emphasize the need for further epizootiological and epidemiological research of TBEV and preventive measures for emerging tick-borne encephalitis in Japan.     

Epidemiological analysis of tick-borne diseases in Zambia

Tick-borne diseases are a constraint to livestock production in many developing countries as they cause high morbidity and mortality, which results in decreased production of meat, milk and other livestock by-products. The most important tick-borne diseases of livestock in sub-Saharan Africa are East Coast fever (caused by Theileria parva), babesiosis (caused by Babesia bigemina and B. bovis), anaplasmosis (caused by Anaplasma marginale) and heartwater (caused by Ehrlichia ruminantium). Despite their economic importance, information on the epidemiology of these diseases in many countries, including Zambia, is often inadequate, making rational disease control strategies difficult to implement. In this study 18S and 16S rRNA gene PCR assays were used for a comprehensive epidemiological analysis of tick-borne disease of cattle in three provinces of Zambia (Lusaka, Central and Eastern). All the disease pathogens under study (T. parva, T. mutans, T. taurotragi, B. bovis, B. bigemina, Anaplasma spp and E. ruminantium) were prevalent in each of the provinces surveyed. However, variation was observed in prevalence between regions and seasons. There was no association between live vaccination against East Coast fever and being PCR positive for T. parva. A number of risk factors were shown to be associated with (a) the occurrence of tick-borne pathogens in cattle and (b) cattle tick burdens in the wet season. A negative association was observed between the number of co-infecting pathogens and the erythrocyte packed cell volume (PCV) of carrier cattle.     

Recent progress in West Nile virus diagnosis and vaccination

ABSTRACT: West Nile virus (WNV) is a positive-stranded RNA virus belonging to the Flaviviridae family, a large family with 3 main genera (flavivirus, hepacivirus and pestivirus). Among these viruses, there are several globally relevant human pathogens including the mosquito-borne dengue virus (DENV), yellow fever virus (YFV), Japanese encephalitis virus (JEV) and West Nile virus (WNV), as well as tick-borne viruses such as tick-borne encephalitis virus (TBEV). Since the mid-1990s, outbreaks of WN fever and encephalitis have occurred throughout the world and WNV is now endemic in Africa, Asia, Australia, the Middle East, Europe and the Unites States. This review describes the molecular virology, epidemiology, pathogenesis, and highlights recent progress regarding diagnosis and vaccination against WNV infections.     

Tick- and flea-borne rickettsial emerging zoonoses

Between 1984 and 2004, nine more species or subspecies of spotted fever rickettsiae were identified as emerging agents of tick-borne rickettsioses throughout the world. Six of these species had first been isolated from ticks and later found to be pathogenic to humans. The most recent example is Rickettsia parkeri, recognized as a human pathogen more than 60 years after its initial isolation from ticks. A new spotted fever rickettsia, R. felis was also found to be associated with fleas and to be a human pathogen. Similarly, bacteria within the family Anaplasmataceae have been considered to be of veterinary importance only, yet three species have been implicated in human diseases in recent years, including Ehrlichia chaffeensis, the agent of human monocytic ehrlichiosis, Anaplasma phagocytophilum, the agent of human anaplasmosis (formerly known as "human granulocytic ehrlichiosis agent", E. equi and E. phagocytophila), and finally Ehrlichia ewingii, which causes granulocytic ehrlichiosis in humans. We present here an overview of the various tick- and flea-borne rickettsial zoonoses described in the last 20 years, focusing on the ecological, epidemiological and clinical aspects.     

Emerging zoonoses

The food-borne zoonoses are the most important zoonoses in England and Wales measured in terms of human morbidity and mortality and they include the most important emerging infections. Over the past decade there were over 100,000 laboratory reported cases of salmonellosis, about 1–5 per cent with serious extra-intestinal complications with 427 registered deaths; there were nearly 90,000 Campylobacter infections. In salmonellosis the sources and modes of spread of infection are largely known, but veterinary and human public health measures have so far failed to control the disease. In Campylobacter enteritis however, the source and spread in most of the reported cases are unknown and control is not yet possible. Amongst the remaining less common food-borne zoonoses, listeriosis and yersiniosis are most prominent. Both are increasing with food-borne outbreaks of both infections having been reported, but the origin of infection of most cases recorded in England and Wales is not known. Of the new food-borne or water-borne diseases the most common are giardiasis and cryptosporidiosis but in neither is it clear whether the infections are predominantly of human or animal origin. The place of haemorrhagic colitis and of S. zooepidemicus infection is not yet apparent, both may emerge as important zoonoses. Streptobacillary fever, on the other hand, seems unlikely to recur with normal hygienic standards of water and milk supply. Of the occupational zoonoses Q fever and leptospirosis are the most important. Although only 1,330 cases of Q fever were reported in 10 years, it is a severe disease; 123 of them had endocarditis. Leptospirosis probably increased in incidence and emerged as a new disease of farmers and others working with cattle. S. suis type 2, a ‘new’ disease, remained a rarity. Zoonoses acquired from pets made up only a small proportion of human zoonotic infections and the only apparent change was an increase in psittacosis, the reason for which is unknown. Lastly, among the zoonoses acquired from wild and captive animals the viral haemorrhagic fevers have emerged as an important hazard in hospitals and laboratories.     

Public Health Argument to Retain Current UK National Controls for Tick and Tapeworms Under the Pet Travel Scheme

At present, the European Council is debating whether the current national controls under the Pet Travel Scheme (PETS), which aims to prevent the introduction of rabies and tapeworms or live ticks and their associated diseases into the United Kingdom (UK), should be harmonized amongst European Union (EU) Member States. There is a strong case to support the retention of control measures on human health grounds. Although many are aware of the implications of rabies infection, few realize the risk to the UK population if current tick and tapeworm controls under PETS were to be removed. If this were to occur, there is a risk that a number of diseases of human health importance may be introduced and become established in the UK. Such diseases include alveolar echinococcosis, tick borne encephalitis, tularaemia and Mediterranean spotted fever; all of which are found in other EU Member States but do not occur in the UK. These four diseases are responsible for a significant burden of disease in Europe, and current national controls under PETS have been highly effective in so far preventing their introduction into the UK.     

AVMA guide for veterinary medical waste management

Lawmakers have enacted a variety of laws and regulations to ensure proper disposal of certain potentially infectious or otherwise objectionable waste. The veterinary medical profession supports scientifically based regulations that benefit public health. In 1988, Congress passed the Medical Waste Tracking Act, a federal program that mandates tracking certain regulated waste. Several types of waste generated in the typical clinical veterinary medical practice are considered regulated veterinary medical waste. Discarded needles, syringes, and other sharps; vaccines and vials that contained certain live or attenuated vaccines; cultures and stocks of infectious agents and culture plates; research animals that were exposed to agents that are infectious to human beings and their associated waste; and other animal waste that is known to be potentially harmful to human beings should be handled as regulated veterinary medical waste. Regulated veterinary medical waste should be handled with care. It should be decontaminated prior to disposal. The most popular, effective methods of decontamination are steam sterilization (autoclaving) and incineration. Chemical decontamination is appropriate for certain liquid waste. Waste should be packaged so that it does not spill. Sharps require rigid puncture- and leak-resistant containers that can be permanently sealed. Regulated veterinary medical waste that has not been decontaminated should be labeled with the universal biohazard symbol. Generators retain liability for waste throughout the entire disposal process. Therefore, it is essential to ensure that waste transporters and disposal facilities comply with state and federal requirements. Veterinary practices should maintain a written waste management program and accurate records of regulated veterinary medical waste disposal. Contingency planning and staff training are other important elements of a veterinary medical waste management program. The guide includes a model veterinary medical waste management program; however, it does not address all the variations in state and local regulations. Veterinarians should obtain copies of state and local laws and regulations and modify AVMA's model plan to create an individualized practice plan that complies with federal, state, and local laws and regulations. State and local veterinary medical organizations should monitor state and local regulation to influence decisions that affect veterinarians and to keep their members informed of changing requirements. Veterinarians and veterinary medical organizations must stay involved so that regulations do not unfairly burden the veterinary medical profession.     

Pathogenicity of endophytic entomopathogenic fungi to Ornithodoros erraticus and Ornithodoros moubata (Acari: Argasidae)

The argasid ticks O. erraticus and O. moubata are of great medical and veterinary importance because they are vectors of the African swine fever virus and several species of human relapsing fever borreliae. Biocontrol of these ticks using entomopathogenic fungi has not been previously reported. We examined the pathogenicity to different developmental stages of these two argasids of six strains of the fungal species Beauveria bassiana (strains Bb1764 and Bb2157), Lecanicillium lecanii (strains Ll586, Ll618 and Ll3047) and Tolypocladium cylindrosporum (strain Tc3398). Three strains, Bb1764, Bb2157, and Tc3398, caused in Spanish O. erraticus mean mortality rates between 34.4% and 62% in 14-28 days post-inoculation. Additionally, Bb2157 also induced in African O. moubata mean mortality rates of 31.9%. The remaining strains caused lower mortality rates and were not considered effective. This is the first study in which some strains of entomopathogenic fungi are found to be effective against argasid ticks of the genus Ornithodoros, and its results might justify further efforts towards the application of entomopathogenic fungal strains as anti-argasid biocontrol agents.     

Relative adrenal insufficiency in critical illness

Objective: To review the effects of critical illness on hypothalamic–pituitary–adrenal (HPA) function in human and veterinary medicine. Data sources: Data from human and veterinary literature was reviewed. Human data synthesis: Relative adrenal insufficiency (RAI) appears to be common in critically ill human patients with sepsis or septic shock. Hypotension that is refractory to fluid therapy and requires vasopressors is the most common presentation of RAI in the human intensive care unit (ICU). Many investigators now advocate the use of a low‐dose adrenocorticotropin hormone stimulation test to diagnose RAI. It is important to evaluate for the presence of adrenal dysfunction, because current data suggest that treatment with ‘stress’ or low doses of glucocorticoids (200–300 mg hydrocortisone daily) may improve patient outcome in humans. Veterinary data synthesis: There is a paucity of controlled studies in the veterinary literature regarding the effects of critical illness on HPA function. The results of these studies are varied. However, research models of sepsis and hemorrhagic shock suggest the existence of RAI in animals. Prospective clinical studies are needed to further examine pituitary–adrenal response to severe illness in veterinary patients, and to determine if there are therapeutic options, including glucocorticoid administration, which will improve patient outcome in animals. Conclusions: RAI is well documented in critically ill human patients, yet little is known about adrenal dysfunction in veterinary critically ill patients. A small number of studies suggest that RAI may exist in certain subpopulations of veterinary patients. The syndrome of RAI could be considered as a differential diagnosis in seriously ill veterinary patients that fail to respond to appropriate therapy, especially when hypotension refractory to fluid and vasopressor therapy is encountered. This disorder may represent a previously unidentified syndrome in critically ill veterinary patients with important therapeutic implications.     

An electron microscopic study of Cytoecetes phagocytophila infection in Ixodes ricinus

Tick-borne fever, caused by a rickettsia-like organism, Cytoecetes phagocytophila, is transmitted by the sheep tick Ixodes ricinus. An electron microscopic technique was developed to examine I ricinus for C phagocytophila infection. Infected and uninfected ticks were obtained from a laboratory maintained tick culture. All stages of I ricinus collected from one field site were examined; 44 per cent of nymphae and 32 per cent of adults were infected with C phagocytophila, but larvae were uninfected. This supports the previously held theory of transtadial, but not transovarial transmission of tick-borne fever.     

Anaplasma phagocytophilum - the most widespread tick-borne infection in animals in Europe

The bacterium Anaplasma phagocytophilum (formerly Ehrlichia phagocytophila) may cause infection in several animal species including human. The disease in domestic ruminants is also called tick-borne fever (TBF), and has been known for at least 200 years. In Europe, clinical manifestations due to A. phagocytophilum have been recorded in sheep, goat, cattle, horse, dog, cat, roe deer, reindeer and human. However, seropositive and PCR-positive mammalian have been detected in several other species. Investigations indicate that the infection is prevalent in Ixodes ricinus areas in most countries in Europe. A. phagocytophilum infection may cause high fever, cytoplasmatic inclusions in phagocytes and severe neutropenia, but is seldom fatal unless complicated by other infections. Complications may include abortions, and impaired spermatogenesis for several months. However, the most important aspect of the infection at least in sheep is its implication as a predisposing factor for other infections. Factors such as climate, management, other infections, individual conditions etc. are important for the outcome of the infection. A. phagocytophilum may cause persistent infection in several species. Based on the 16S rRNA gene sequences several variants exist. Different variants may exist within the same herd and even simultaneously in the same animal. Variants may behave differently and interact in the mammalian host.     

The current status of major tick borne diseases in Zambia

Tick-borne diseases occurring in Zambia are assuming more importance as they continue to be a major economic problem not only in Zambia, but in many parts of Eastern, Southern and Central Africa. The current control methods, which include the use of toxic acaricides to kill ticks, and the virulent sporozoite infection and treatment method have limitations. Recombinant vaccines, currently in their experimental stages, offer hope for the future. The use of acaricides is hampered by the development of acaricide resistance and live vaccines are dependent on cold chain facilities, which are a formidable obstacle in the poorly developed infrastructure in parts of Zambia where the vaccine is most needed. Amidst these drawbacks are the results of the recent research on parasites and vector recombinant vaccines which promise to circumvent these problems. The history, current status and attitudes regarding the control of these diseases, taking into account their complexity, are reviewed. The establishment of the well-designed Central Veterinary Research Institute (CVRI) and Japanese International Cooperation Agency (JICA) sponsored veterinary school, both have a potential for high quality research, with access to a wealth of specimens a veritable goldmine of research material. It is thus hoped that this review will stimulate the desire to maximize the value of the tick and tick-borne disease research in both Zambia and the international research community.     

Cellular adhesive phenomena in apicomplexan parasites of red blood cells

The apicomplexan parasites Babesia and Plasmodium are related, yet phylogenetically distinct haemoprotozoa that infect red blood cells and cause severe diseases of major human and veterinary importance. A variety of cellular and molecular interactions are pivotal in many aspects of the pathogenicity of these two parasites. Comparison of the cellular and molecular mechanisms that culminate in accumulation of parasitised red blood cells in the microvasculature of cattle infected with Babesia bovis (babesiosis) and humans infected with Plasmodium falciparum (falciparum malaria) is particularly instructive given the striking similarities in the pathophysiology of these two important medical and veterinary diseases. While such adhesive phenomena have been studied extensively in malaria, they have received relatively little attention in babesiosis. In this review, we summarise the findings of more than 25 years of research into cellular adhesive phenomena in malaria and speculate on how this body of work can now be applied to Babesia parasites. Such information is fundamental if we are to learn more about the biology of Babesia parasites, the cellular and molecular mechanisms by which they cause infection and disease and how to develop novel therapeutic strategies or vaccines for both Babesia and malaria infections.     

Visceral larva migrans and alveolar hydatid disease. Dangers real or imagined.

For both visceral larva migrans and alveolar hydatid diseases, it is the feces of companion animals that are the primary source of human infection. Clearly, whatever is done to reduce this form of environmental contamination and the prevalence of the parasites' infective stages will help to protect the health of the human population in the United States and Canada, particularly the children. Very important are appropriate anthelmintic treatment programs, especially for T. canis, and proper control of close associations between pets and people. Probably the known incidence of visceral larva migrans in humans and the range of its known pathogenicity will increase as better diagnostic methods become available. In addition, other animal helminths, for instance Toxocara cati and Toxascaris leonina, may become more substantially documented as causes of human visceral larva migrans. Until more is known of the geographical distribution and prevalence of Echinococcus multilocularis among animals in North America, it will be difficult to assess accurately the future significance of alveolar hydatid disease in the continent's human population. Another important advance would be the development of anthelmintics that are effective for somatic second stage larvae of T. canis, and others effective for adult or larval Echinococcus species. Meanwhile it is a most important responsibility of the veterinary profession to educate its clients thoroughly concerning these dangerous helminths.     

Epidemic patterns of encephalitis, hemorrhagic fever and rabies in Korea (1979–1988)

In 1983, 1197 human cases (3.04/10 000 population) of epidemic encephalitis were reported, but practically no further cases of this condition have been reported since 1984. Human cases of encephalitis occurred primarily among those younger than 19 years in rice-field regions in the autumn. The mean number of patients registered annually with hemorrhagic fever from 1979 to 1988 was 46.5 (0.19/10 000 population), being highest in 1979 (73 cases, 0.19/10 000) and lowest in 1982 (32 cases, 0.08/10 000). Hemorrhagic fever occurred among adults mainly in autumn in mountain regions. Two cases of rabies in human and dog were reported in 1984.