Smallpox vaccination and bioterrorism with pox viruses

Bioterrorist attacks occupy a special place amongst the innumerable potential types of terrorist attack, with the intentional release of pox viruses being especially feared in this connection. Apart from the variola virus, the agent responsible for smallpox in humans, the monkeypox virus and numerous other animal pox viruses pose potential risks for humans and animals. This risk scenario also includes recombinations between the various pox viruses, changes in hosts and genetically engineered manipulations of pox viruses.

For over 200 years, the method of choice for combatting smallpox was via vaccination with a reproductive, original vaccinia virus. Worldwide eradication of smallpox at the end of the 1970s and the discontinuation of routine smallpox vaccination in 1980 can be credited to such vaccination. Unfortunately, these vaccinations were associated with a large number of postvaccinal impairments, sometimes resulting in death (e.g. postvaccinal encephalitis). The only way to restrict such postvaccinal complications was to carry out initial vaccination within the first 2 postnatal years. Initial vaccination at a later age led to such a sharp increase in the number of vaccines with complications that vaccination had to be discouraged.

The dilemma of the smallpox vaccine stocks stems from the fact that a large portion of these stocks are produced with the same vaccinia strains as before. This is irresponsible, especially as the percentage of immune-suppressed persons in the population, for whom vaccination-related complications pose an especial threat, is increasing.

One solution to the dilemma of the smallpox vaccine stocks is the MVA strain. It is harmless, protects humans and animals equally well against smallpox and can be applied parenterally.     

Substitution of vaccinia virus Elstree by modified vaccinia virus Ankara to test the virucidal efficacy of chemical disinfectants

After the eradication of variola in 1980, the smallpox vaccination was considered to be no longer required and was subsequently abandoned mainly because of possible adverse effects of vaccinia virus especially in first‐time vaccinees. Despite a growing number of humans without immunity against vaccinia virus, vaccinia virus Lister Elstree (VACV) is still prescribed for testing virucidal efficacy of chemical disinfectants in the guidelines of the German Veterinary Medical Society [Deutsche Veterinärmedizinische Gesellschaft (DVG)], the German Association for the Control of Virus Diseases [Deutsche Vereinigung zur Bekämpfung der Viruskrankheiten (DVV)] and the Robert Koch Institute (RKI). To evaluate a possible substitution of VACV, with the attenuated modified vaccinia virus Ankara (MVA) the virucidal efficacy of four different DVG‐listed commercially available chemical disinfectants representing different groups of chemicals was tested against these two viruses. Quantitative suspension tests and qualitative carrier tests with poplar wood and gauze were performed. Distinction of VACV and MVA was confirmed by cytopathogenic effects, such as differences in plaque morphology. No significant difference in disinfection efficacy between VACV and MVA was observed for any of the disinfectants tested. Implying that vaccinia virus poses a risk after inadvertent inoculation, our results show that MVA, which does not replicate in humans, should replace VACV in the chemical disinfectant testing guidelines.     

Bluetongue vaccines in Europe

The article reviews the history, present status and the future of BT vaccines in Europe. So far, an attenuated (modified live viruses, MLV) and inactivated virus vaccines against BT were developed and used in the field. Moreover, the virus-like particles (VLPs) produced from recombinant baculovirus, and live recombinant vaccinia or canarypox virus-vectored vaccines were tested in the laboratory. The main aims of BT vaccination strategy are: to prevent clinical disease, to reduce the spread of the BTV in the environment and to protect movement of susceptible animals between affected and free zones. Actually, all of the most recent European BT vaccination campaigns have used exclusively inactivated vaccines. The use of inactivated vaccines avoid risk associated with the use of live-attenuated vaccines, such as reversion to virulence, reassortment of genes with field strain, teratogenicity and insufficient attenuation leading to clinical disease. The mass vaccinations of all susceptible animals are the most efficient veterinary method to fight against BT and successful control of disease. The vaccination of livestock has had a major role in reducing BTV circulation and even in eradicating the virus from most areas of Europe.     

New emerging viral zoonoses

New developments in the field of viral transmission from animal to man can be divided into four areas of study. First are the new viral zoonoses such as diseases caused by rotaviruses, Lassa virus and the animal orthopox viruses which will be more prevalent after the cessation of mandatory vaccination against smallpox. Secondly are the numerous ubiquitous viruses, such as adeno and herpesviruses, which in healthy animals lead only to clinically inapparent infections. A typical example of the third area is the recombination and hybridisation between animal and human influenza type A viruses. The final area is concerned with the transmission of viral zoonoses to man through food of animal origin.     

Immunization of cattle against Aujeszky's disease with inactivated adjuvant vaccine

The experiments with sheep and young cattle were carried out to test the immunizing efficacy of inactivated adjuvant vaccine against Aujeszky's disease. The vaccine application at doses of 1 ml and 2 ml to lambs at the age of eight to ten months caused the neutralizing antibody production with a significant rise of titres after revaccination. A survival of infection induced with a dose of 10(5.5) TKID50 of virulent virus was recorded in 62.5% of once vaccinated animals and in 87.5% of twice vaccinated animals. When applying different doses of vaccines (from 1 to 10 ml) to young cattle, the antibody reaction level was directly dependent on the inoculum quantity. The double inoculation of animals with vaccines of 2 ml and 5 ml caused the neutralizing antibody production at titres of 1:35, or 1:46. The animals, immunized with the live or inactivated IBR-vaccine possessing high antibody titres against IBR-virus, reacted upon the vaccination with inactivated Aujeszky's vaccine anamnestically, by early production of antibodies in high titres. Metaphylactic vaccination (2 ml of vaccine) of cattle in herds with an acute course days, however earlier during five days from the revaccination when it was carried out in seven days following the first vaccination.     

Taking advantage of the positive side-effects of smallpox vaccination

From the introduction of smallpox vaccination approximately 200 years ago right up to its discontinuation (1980), reports by physicians and scientists about positive side-effects such as healing of chronic skin rashes, reduced susceptibility to various infectious diseases, e.g. measles, scarlet fever and whooping cough, and even the prophylactic use of the vaccination, e.g. against syphilis, were published again and again. Comparison with the period after cessation of vaccination confirms the experiences of the above vaccinators. As early as 1956, targeted research on these observations led to evidence of the 'ring-zone phenomenon', i.e. the production of soluble antiviral substances in infected chicken embryos and cell cultures. With the help of modern immunological and bioengineering methods, it was later possible to demonstrate that these effects are based on the activation of lymphoreticular cells and the regulatory effect of certain cytokines within the context of the non-specific immune system. These findings led to the development of paramunization with paraspecific vaccines from highly attenuated animal pox viruses. During attenuation, deletions in the virus DNA occur. Attenuated animal pox strains are therefore suited for the production of vector vaccines. The fact that these vector vaccines demonstrate an especially high level of paraspecific efficacy and lack harmful effects is likewise the result of the attenuated animal pox viruses. Optimum regulation of the entire immune system leads to increased paramunity already in the first few days after vaccination and to enhanced antigen recognition and thus accelerated commencement of specific immunity.     

Animal poxviruses transmitted from cat to man: current event with lethal end.

We report about the infection of an 18-year-old man with an orthopox virus (OPV) which was transmitted by a cat. The infectious route from cat to man could be proved by epidemiological, virological and serological methods. The corresponding techniques are described. The patient had not been vaccinated against smallpox and was intensively immunosuppressed by medication on account of a severe endogeneous eczema combined with an allergic asthma bronchiale. A cyclic poxvirus disease developed with a generalised, partly confluent pox virus exanthema disseminated over the body. The clinical symptoms were similar to a "variola pustulosa haemorrhagica". The young man died of a lung embolism in the course of the intensive medical therapy. The haemorrhagic character of the pox virus pustules with central necrosis (pox navel) could be reproduced in the rabbit skin and on chorioallantois membranes. The pox virus isolated from the patient could be differentiated from variola, vaccinia and monkeypox virus. It is a member of the group of "cowpox-like viruses". The environmental importance of these OPVs is discussed.     

Poxviruses as vaccine vectors

The discovery of Jenner in 1798 founded the science of immunology and eventually led to smallpox eradication from the earth in 1980 after a world-wide vaccination campaign with vaccinia virus (another poxvirus) and paradoxically, despite the eradication of smallpox, there has been an explosion of interest in vaccinia virus in the eighties. This interest has stemmed in part from the application of molecular genetics to clone and express foreign genes from recombinant vaccinia viruses. Vaccinia is also gaining renewed interest due to bioterrorism.

These recombinant viruses have multiple applications in research and vaccinology and led to the development of vectored vaccines, such as the recombinant vaccinia rabies vaccine used to eliminate rabies in Western Europe and, more recently, in the United States. Secondly, alternative poxvirus vectors, such as avipox viruses, were proved to be even safer and efficacious non-replicating vectors (suiciole vectors) when used in non-avian species.     

Potency of an experimental DNA vaccine against Aujeszky's disease in pigs

Intradermal vaccination with plasmid DNA encoding envelope glycoprotein C (gC) of pseudorabies virus (PrV) conferred protection of pigs against Aujeszky's disease when challenged with strain 75V19, but proved to be inadequate for protection against the highly virulent strain NIA-3. To improve the performance of the DNA vaccine, animals were vaccinated intradermally with a combination of plasmids expressing PrV glycoproteins gB, gC, gD, or gE under control of the major immediate-early promotor/enhancer of human cytomegalovirus. 12.5 microg per plasmid were used per immunization of 5-week old piglets which were injected three times at biweekly intervals. Five out of six animals survived a lethal challenge with strain NIA-3 without exhibiting central nervous signs, whereas all the control animals succumbed to the disease. This result shows the increased protection afforded by administration of the plasmid mixture over vaccination with a gC expressing plasmid alone. A comparative trial was performed using commercially available inactivated and modified-live vaccines and a mixture of plasmids expressing gB, gC, and gD. gE was omitted to conform with current eradication strategies based on gE-deleted vaccines. All six animals vaccinated with the live vaccine survived the lethal NIA-3 challenge without showing severe clinical signs. In contrast, five of six animals immunized with the inactivated vaccine died, as did two non-vaccinated controls. In this test, three of six animals vaccinated with the DNA vaccine survived without severe clinical signs, whereas three succumbed to the disease. Comparing weight reduction and virus excretion, the DNA vaccine also ranged between the inactivated and modified-live vaccines. Thus, administration of DNA constructs expressing different PrV glycoproteins was superior to an adjuvanted inactivated vaccine but less effective than an attenuated live vaccine in protection of pigs against PrV infection. Our data suggest a potential use of DNA vaccination in circumstances which do not allow administration of live attenuated vaccines.     

Vaccination against chlamydial infections of man and animals

Vaccination is the best approach for controlling the spread of chlamydial infections, in animal and human populations. This review summarises the progress that has been made towards the development of effective vaccines over the last 50 years, and discusses current vaccine strategies. The ultimate goal of vaccine research is to develop efficacious vaccines that induce sterile, long-lasting, heterotypic protective immune responses. To date, the greatest success has been in developing whole organism based killed or live attenuated vaccines against the animal pathogens Chlamydophila abortus and Chlamydophila felis. However, similar approaches have proved unsuccessful in combating human chlamydial infections. More recently, emphasis has been placed on the development of subunit or multicomponent vaccines, as cheaper, safer and more stable alternatives. Central to this is a need to identify candidate vaccine antigens, which is being aided by the sequencing of representative genomes of all of the chlamydial species. In addition, it is necessary to identify suitable adjuvants and develop methods for antigen delivery that are capable of eliciting mucosal and systemic cellular and humoral immune responses. DNA vaccination in particular holds much promise, particularly in terms of safety and stability, although it has so far been less effective in humans and large animals than in mice. Thus, much research still needs to be done to improve the delivery of plasmid DNA, as well as the expression and presentation of antigens to ensure that effective immune responses are induced.     

Developing vaccines to control protozoan parasites in ruminants: dead or alive?

Protozoan parasites are among some of the most successful organisms worldwide, being able to live and multiply within a very wide range of hosts. The diseases caused by these parasites cause significant production losses in the livestock sector involving reproductive failure, impaired weight gain, contaminated meat, reduced milk yields and in severe cases, loss of the animal. In addition, some protozoan parasites affecting livestock such as Toxoplasma gondii and Cryptosporidium parvum may also be transmitted to humans where they can cause serious disease. Data derived from experimental models of infection in ruminant species enables the study of the interactions between parasite and host. How the parasite initiates infection, becomes established and multiplies within the host and the critical pathways that may lead to a disease outcome are all important to enable the rational design of appropriate intervention strategies. Once the parasites invade the hosts they induce both innate and adaptive immune responses and the induction and function of these immune responses are critical in determining the outcome of the infection. Vaccines offer green solutions to control disease as they are sustainable, reducing reliance on pharmacological drugs and pesticides. The use of vaccines has multiple benefits such as improving animal health and welfare by controlling animal infections and infestations; improving public health by controlling zoonoses and food borne pathogens in animals; solving problems associated with resistance to acaricides, antibiotics and anthelmintics; keeping animals and the environment free of chemical residues and maintaining biodiversity. All of these attributes should lead to improved sustainability of animal production and economic benefit. Using different protozoan parasitic diseases as examples this paper will discuss various approaches used to develop vaccines to protect against disease in livestock and discuss the relative merits of using live versus killed vaccine preparations. A range of different vaccination targets and strategies will be discussed to help protect against: acute disease, congenital infection and abortion, persistence of zoonotic pathogens in tissues of food animals and passive transfer of immunity to neonates.     

Immunoprophylaxis of bovine dermatophytosis.

The literature on immunoprophylaxis as control method for ringworm in cattle is reviewed. Scientific papers on immune response to dermatophyte antigens and vaccination against ringworm were obtained from personal files and computerized search in 4 relevant databases. Vaccines with antigens of Trichophyton verrucosum stimulate a humoral and cellular immune response. In animals vaccinated with inactivated vaccines, some protection is observed after challenge. However, the protective immunity is inadequate in most cases. Vaccination with live vaccines elicits an immune response that prevents the development of clinical disease. The protective immunity is based mainly on the cellular branch of the immune system. The efficacy and safety of live dermatophyte vaccines have been demonstrated in both challenge experiments and field trials from different countries. Effective control of ringworm in cattle has been achieved in regions implementing systematic vaccination.     

Efficacy of vaccines against bacterial diseases in swine: what can we expect?

This paper discusses what can be expected with regard to efficacy of antibacterial vaccines used in swine, based on the present knowledge of pathogen–host interactions. First, vaccination against bacteria that mainly cause disease by production of exotoxins is considered. Vaccines containing the inactivated toxin or a non-toxic but antigenic recombinant protein derived from the exotoxin can be expected to provide protection against disease. The degree of protection induced by such vaccines varies, however, depending amongst other things on the pathogenesis of the disease. Vaccination against clostridial infections, Actinobacillus pleuropneumoniae infections, progressive atrophic rhinitis and enterotoxigenic Escherichia coli, is considered. The second part of the article deals with vaccination against extracellular bacteria. Protection against these bacteria is generally mediated by antibodies against their surface antigens and certain secreted antigens, but cellular immunity may also play a role. Efficacy of vaccines against swine erysipelas, Streptococcus suis infections, Mycoplasma hyopneumoniae infections and swine dysentery is discussed. Finally, vaccination against facultatively intracellular bacteria is considered. For protection against these bacteria cell-mediated immunity plays an important role, but antibodies may also be involved. It is generally accepted that live-attenuated vaccines are more suitable for induction of cell-mediated immunity than inactivated vaccines, although this also depends on the adjuvant used in the vaccine. As an example, vaccination against Salmonella enterica serotype Typhimurium is discussed.     

Gordon memorial lecture. Vaccines and vaccination--past, present and future

1. Immunisation was first practised as early as the 10th century when small doses of smallpox material administered by unusual routes were used to immunise against smallpox. The procedure was introduced into England in the early part of the 18th century. 2. The next major development was the use by Jenner of cowpox to vaccinate against smallpox in the late 18th century. 3. Some eighty years later came the classic studies of Pasteur developing vaccines for fowl cholera, anthrax and rabies. 4. The studies of Jenner and Pasteur established the major principles of vaccination which are in use to this day. 5. The major viral diseases of the domestic fowl were recognised during the 1920s and 1930s and in most cases vaccines were developed within 5 years of the discovery of the viral nature of the cause of each disease. 6. The desirable properties of poultry vaccines required by the user and producer are not completely fulfilled by currently available vaccines. 7. There is a need to use the opportunities provided by modern biotechnology and immunology to search for and develop vaccines that better fulfil the desirable properties of poultry vaccines. 8. There are a number of strategies available for the development of novel vaccines, some of which are appropriate for the needs of poultry vaccines.     

Characterization of the long-term immune response to vaccination against Mycobacterium avium subsp. paratuberculosis in Danish dairy cows

Vaccination of cattle against Mycobacterium avium subsp. paratuberculosis (MAP) provides partial protection by delayed shedding of MAP and reduced numbers of clinically affected animals. The duration of vaccine induced immune response is not known. The primary objective of this study was therefore to characterize the long-term effect of whole-cell based vaccination against MAP on the immune response. A secondary objective was to evaluate whether immunodiagnosis of MAP and Mycobacterium bovis infections is affected by MAP vaccination. Two studies were performed: (1) A retrospective longitudinal study including 895 vaccinated and 2526 non-vaccinated dairy cows in 9 Danish dairy herds aiming at characterizing the long-term antibody-response to vaccination; and (2) a cross-sectional study of responses in the IFN-γ assay carried out in 140 vaccinated animals in two herds to evaluate the effect of vaccination on the cell-mediated immune response and to evaluate a possible interference with the diagnosis of M. bovis infections. The results showed that 37% of samples from vaccinated animals and 5% of samples from non-vaccinated animals, respectively, were test positive in the milk antibody ELISA. The prevalence of antibody responses of the vaccinated animals was relatively constant from 2 to 6 years of age, but decreased in older animals. Among the 140 vaccinated animals 88% tested positive with the IFN-γ test to johnin PPD and 50% responded to PPDb with IFN-γ production above a similar cut-off. Although Denmark is free of M. bovis, two of the vaccinated animals responded with higher IFN-γ levels when cultured with PPDb compared to PPDa. In conclusion, immunization with whole-cell MAP vaccines elicits both humoral and cell-mediated immune reactions, which may interfere with surveillance and diagnosis of both MAP and M. bovis infections using currently available tests.     

抗猪繁殖与呼吸综合征高免血清的研制

为研制用于治疗和预防猪繁殖与呼吸综合征的高免血清,选取健康育肥猪作为免疫接种对象,用猪繁殖与呼吸综合征灭活苗和弱毒苗作基础免疫和强化免疫,通过优化免疫程序,制备出抗猪繁殖与呼吸综合征高免血清,并进行了临床治疗试验,结果总有效率为86.67%。表明采用这种方法制备猪繁殖与呼吸综合征高免血清是安全有效、切实可行的。     

Live vaccines against bovine babesiosis

Bovine babesiosis is an important tick-borne disease caused by Babesia bovis, B. bigemina and B. divergens. The first steps taken in the development of an effective vaccination strategy against bovine babesiosis followed the observations that animals, recovered from natural infection with Babesia were strongly protected against subsequent challenge. Further investigation indicated that the use of donor blood from recovered animals to infect recipient animals did not produce the severe form of the disease. The past century has seen a refinement of this original carrier-donor system to one using attenuated less virulent strains with standardized doses of known parasite concentration to ensure reliability. With the implementation of good manufacturing practices further changes were necessary in the production of these vaccines, such as freezing for long-term storage to allow sufficient time for pre-release safety and effectivity testing. Regardless of these improvements the vaccines are not without problems and breakdowns and breakthroughs occur from time to time. Despite considerable research efforts into the development of alternative more consumer friendly vaccines, none is immediately forthcoming and the live attenuated babesiosis vaccines are still used in many countries.     

Comparative evaluation of live marker vaccine candidates "CP7_E2alf" and "flc11" along with C-strain "Riems" after oral vaccination

Due to the tremendous socio-economic impact of classical swine fever (CSF) outbreaks, emergency vaccination scenarios are continuously under discussion. Unfortunately, all currently available vaccines show restrictions either in terms of marker capacities or immunogenicity. Recent research efforts were therefore directed at the design of new modified live marker vaccines. Among the most promising candidates the chimeric pestiviruses "CP7_E2alf" and "flc11" were identified. Within an international research project, these candidates were comparatively tested in challenge experiments after a single oral vaccination. Challenge infection was carried out with highly virulent CSF virus strain "Koslov", 14 or 21 days post vaccination (dpv), respectively. Safety, efficacy, and marker potential were addressed. All assessments were done in comparison with the conventional "gold standard" C-strain "Riems" vaccine. In addition to the challenge trials, multiple vaccinations with both candidates were performed to further assess their marker vaccine potential. All vaccines were safe and yielded full protection upon challenge 21 days post vaccination. Neither serological nor virological investigations showed major differences among the three vaccines. Whereas CP7_E2alf also provided clinical protection upon challenge at 14 days post vaccination, only 50% of animals vaccinated with flc11, and 83% vaccinated with C-strain "Riems" survived challenge at this time point. No marked differences were seen in protected animals. Despite the fact that all multiple-vaccinated animals stayed sero-negative in the accompanying marker test, the discriminatory assay remains a weak point due to delayed or inexistent detection of some of the vaccinated and subsequently infected animals. Nevertheless, the potential as live marker vaccines could be confirmed for both vaccine candidates. Future efforts will therefore be directed at the licensing of "Cp7_E2alf" as the first live marker vaccine for CSF.     

牛结节性皮肤病病毒研究进展

牛结节性皮肤病(LSD)在全世界范围内均有流行和记载,对我国养牛业构成了严重的威胁。接种疫苗是目前防控LSDV最有效的方法,其中减毒活疫苗在许多国家均有使用。近年研究表明,LSDV活疫苗的使用会造成疫苗重组病毒的流行,接种后会引起动物不同程度的不良反应。对LSDV的病原学特征、分离鉴定方法、流行病学的情况、检测方法以及LSDV疫苗的研究进展进行了阐述,以期为牛结节性皮肤病的免疫预防以及鉴别诊断提供研究思路。     

Zoonotic poxviruses

Poxviruses compromise a group of long known important pathogens including some zoonotic members affecting lifestock animals and humans. While whole genome sequence analysis started to shed light into the molecular mechanisms underlying host cell infection, viral replication as well as virulence, our understanding of poxvirus maintenance in nature and their transmission to humans is still poor. During the last two decades, reports on emerging human monkeypox outbreaks in Africa and North America, the increasing number of cowpox virus infections in cats, exotic animals and humans and cases of vaccinia virus infections in humans in South America and India reminded us that – beside the eradicated smallpox virus – there are other poxviruses that can cause harm to men. We start to learn that the host range of some poxviruses is way broader than initially thought and that mainly rodents seem to function as virus reservoir. The following review is aiming to provide an up-to-date overview on the epidemiology of zoonotic poxviruses, emphasizing orthopoxviruses. By outlining the current knowledge of poxvirus transmission, we hope to raise the awareness about modes of acquisition of infections and their proper diagnosis.