Poxes great and small: The stories behind their names

The word "pox" indicated, during the late 15th century, a disease characterized by eruptive sores. When an outbreak of syphilis began in Europe during that time, it was called by many names, including the French term "la grosse verole" ("the great pox"), to distinguish it from smallpox, which was termed "la petite verole" ("the small pox"). Chickenpox was initially confused with smallpox until 1767, when the English physician William Heberden (1710-1801) provided a detailed description of chickenpox, differentiating it from smallpox. The cowpox virus was used by Edward Jenner (1749-1823) to develop a successful vaccine against smallpox. He devised the term "variolae vaccinae" ("smallpox of the cow") to denote cowpox. Jenner's pioneering work on a smallpox vaccine has led to the eradication of this disease and opened the way to preventing other infectious diseases, such as monkeypox, a poxvirus that is closely related to smallpox and that is currently infecting persons around the world. This contribution tells the stories behind the names of the various "poxes" that have infected humans: the great pox (syphilis), smallpox, chickenpox, cowpox, and monkeypox. These infectious diseases not only share a common "pox" nomenclature, but are also closely interconnected in medical history.

Field Trial Vaccination against Cowpox in Two Alpaca Herds

In Europe, cowpox virus (CPXV) infection in South American camelids occurs as a so-called spill-over infection. Although infected animals generally have a mild form of the disease and survive, cases of fatal generalised CPXV infection have also been described. Prevention by prophylactic vaccination is the only way to protect animals from disease. In the present study, modified vaccinia virus Ankara (MVA) vaccine, which has been successfully used in many animal species, was used in a prime-boost vaccination regimen in two alpaca herds with a history of CPXV infection. The focus of the study was the prevention of further clinical cases, and to determine the safety and immunogenicity of the MVA vaccine in alpacas. The MVA vaccine was well tolerated and safe in the 94 animals vaccinated. An indirect immunofluorescence assay (IFA) using MVA as an antigen showed that the seroprevalence of antibody after booster vaccination was 81.3% in herd I and 91.7% in herd II. Detectable antibody titres declined to 15.6% in herd I and 45.8% in herd II over a 12-month period after booster vaccination. Animals could be divided into four groups based on individual antibody titres determined over one year: Group 1 consisted of 19.3% of animals that were seropositive until the end of the trial period; Group 2 consisted of 58.0% of animals that were seropositive after booster vaccination, but seronegative one year later; Group 3 consisted of 14.7% of animals that were not seropositive at any time point; and Group 4 consisted of 7.9% of animals that were seropositive after initial immunisation, seronegative six months later, but seropositive or intermediate in IFA one year after immunisation, likely because of natural exposure. In new-born crias born to MVA-vaccinated mares, specific maternal antibodies were detected in 50.0% of animals up to 14 weeks of age. Our results confirm that MVA vaccination is a feasible tool for the prevention of CPXV disease in alpacas. Long-term studies are needed to verify future vaccination regimen in CPXV affected herds.

Effects of nasal or pulmonary delivered treatments with an adenovirus vectored interferon (mDEF201) on respiratory and systemic infections in mice caused by cowpox and vaccinia viruses

An adenovirus 5 vector encoding for mouse interferon alpha, subtype 5 (mDEF201) was evaluated for efficacy against lethal cowpox (Brighton strain) and vaccinia (WR strain) virus respiratory and systemic infections in mice. Two routes of mDEF201 administration were used, nasal sinus (5-µl) and pulmonary (50-µl), to compare differences in efficacy, since the preferred treatment of humans would be in a relatively small volume delivered intranasally. Lower respiratory infections (LRI), upper respiratory infections (URI), and systemic infections were induced by 50-µl intranasal, 10-µl intranasal, and 100-µl intraperitoneal virus challenges, respectively. mDEF201 treatments were given prophylactically either 24 h (short term) or 56d (long-term) prior to virus challenge. Single nasal sinus treatments of 10(6) and 10(7) PFU/mouse of mDEF201 protected all mice from vaccinia-induced LRI mortality (comparable to published studies with pulmonary delivered mDEF201). Systemic vaccinia infections responded significantly better to nasal sinus delivered mDEF201 than to pulmonary treatments. Cowpox LRI infections responded to 10(7) mDEF201 treatments, but a 10(6) dose was only weakly protective. Cowpox URI infections were equally treatable by nasal sinus and pulmonary delivered mDEF201 at 10(7) PFU/mouse. Dose-responsive prophylaxis with mDEF201, given one time only 56 d prior to initiating a vaccinia virus LRI infection, was 100% protective from 10(5) to 10(7) PFU/mouse. Improvements in lung hemorrhage score and lung weight were evident, as were decreases in liver, lung, and spleen virus titers. Thus, mDEF201 was able to treat different vaccinia and cowpox virus infections using both nasal sinus and pulmonary treatment regimens, supporting its development for humans.

Sporadic human cases of cowpox in Germany

Cowpox has been enzootic in cattle for a long time. Over the past years, however, no cowpox virus infections of cattle were diagnosed in Germany. Instead, cowpox viruses are increasingly found in cats, which can develop lesions and secrete large amounts of virus.

Vaccination with Venezuelan equine encephalitis replicons encoding cowpox virus structural proteins protects mice from intranasal cowpox virus challenge

An anti-poxvirus vaccine based on replicon particles of Venezuelan equine encephalitis virus (VRP) is being developed. The cowpox virus genes encoding structural proteins corresponding to vaccinia virus proteins A33, B5, and A27 were each expressed from VRP. High serum IgG titers against these proteins were generated in BALB/c mice vaccinated with each of these VRP. VRP induced both IgG1 and IgG2a with a strong predominance of IgG2a production. The response is long-lasting, as evidenced by the retention of high anti-B5 serum IgG titers through at least 50 weeks after priming immunization. Mice vaccinated with B5-, A33- or A27-VRP individually or together survived intranasal challenge with cowpox virus, with the multivalent vaccine formulation providing more effective protection from weight loss and clinical signs of illness than the monovalent vaccines. These results demonstrate that VRP may provide an effective alternative to vaccinia virus vaccines against poxvirus infection.

Inference of cowpox virus transmission rates between wild rodent host classes using space-time interaction

There have been virtually no studies of 'who acquires infection from whom' in wildlife populations, but patterns of transmission within and between different classes of host are likely to be reflected in the spatiotemporal distribution of infection among those host classes. Here, we use a modified form of K-function analysis to test for space-time interaction among bank voles and wood mice infectious with cowpox virus. There was no evidence for transmission between the two host species, supporting previous evidence that they act as separate reservoirs for cowpox. Among wood mice, results suggested that transmission took place primarily between individuals of the opposite sex, raising the possibility that cowpox is sexually transmitted in this species. Results for bank voles indicated that infected females might be a more important source of infection to either sex than are males. The suggestion of different modes of transmission in the two species is itself consistent with the apparent absence of transmission between species.

Aerosolized cidofovir is retained in the respiratory tract and protects mice against intranasal cowpox virus challenge

We employed a murine model to test the concept of using an aerosolized, long-acting antiviral drug to protect humans against smallpox. We previously showed that a low dose of aerosolized cidofovir (HPMPC [Vistide]) was highly protective against subsequent aerosolized cowpox virus challenge and was more effective than a much larger dose of drug given by injection, suggesting that aerosolized cidofovir is retained in the lung. Because the nephrotoxicity of cidofovir is a major concern in therapy, delivering the drug directly to the respiratory tract might be an effective prophylactic strategy that maximizes the tissue concentration at the site of initial viral replication, while minimizing its accumulation in the kidneys. In the present study, we found that treating mice with aerosolized (14)C-labeled cidofovir ((14)C-cidofovir) resulted in the prolonged retention of radiolabeled drug in the lungs at levels greatly exceeding those in the kidneys. In contrast, subcutaneous injection produced much higher concentrations of (14)C-cidofovir in the kidneys than in the lungs over the 96-h time course of the study. As further evidence of the protective efficacy of aerosolized cidofovir, we found that aerosol treatment before or after infection was highly protective in mice challenged intranasally with cowpox virus. All or nearly all mice that were treated once by aerosol, from 2 days before to 2 days after challenge, survived intranasal infection, whereas all placebo-treated animals died.

Treatment of aerosolized cowpox virus infection in mice with aerosolized cidofovir

The Brighton strain of cowpox virus causes lethal bronchopneumonia when delivered as a small-particle (1 microm) aerosol to weanling BALB/c mice. We showed previously that this disease can be prevented or cured with one subcutaneous injection of cidofovir (HPMPC, Vistide). To determine whether even better results could be obtained by delivering the drug directly to the respiratory tract, we administered cidofovir by small-particle aqueous aerosol before or after aerosolized cowpox infection. In a series of five experiments, aerosol doses of 0.5-5 mg/kg were always more effective than 25 mg/kg and sometimes more effective than 100 mg/kg injected subcutaneously, as measured by changes in body and lung weight, lung viral titers, pulmonary pathology and survival. A cyclic analog ((1-[(S)-2-hydroxy-2-oxo-1,4,2-dioxaphosphorinan-5-yl)methyl] cytosine) (cHPMPC) was less protective. The results suggest that aerosolized cidofovir would be effective for prophylaxis or early post-exposure therapy of human smallpox or monkeypox virus infection.

Cidofovir protects mice against lethal aerosol or intranasal cowpox virus challenge

The efficacy of cidofovir for treatment of cowpox virus infection in BALB/c mice was investigated in an effort to evaluate new therapies for virulent orthopoxvirus infections of the respiratory tract in a small animal model. Exposure to 2(-5)x10(6) pfu of cowpox virus by aerosol or intranasally (inl) was lethal in 3- to 7-week-old animals. One inoculation of 100 mg/kg cidofovir on day 0, 2, or 4, with respect to aerosol infection, resulted in 90%-100% survival. Treatment on day 0 reduced peak pulmonary virus titers 10- to 100-fold, reduced the severity of viral pneumonitis, and prevented pulmonary hemorrhage. The same dose on day -6 to 2 protected 80%-100% of inl infected mice, whereas 1 inoculation on day -16 to -8 or day 3 to 6 was partially protective. Cidofovir delayed but did not prevent the death of inl infected mice with severe combined immunodeficiency. Treatment at the time of tail scarification with vaccinia virus did not block vaccination efficacy.

[Biohazards due to Orthopoxvirus: should we re-vaccinate against smallpox?]

Although the WHO declared global smallpox eradication in 1980, the Orthopoxvirus remains a source of concern for several reasons. Firstly, stocks of the smallpox virus have been preserved for experimental use (at least officially in the USA and Russia) so that an escaped isolate could lead to reemergence and spread of the disease worldwide. Secondly discontinuation of smallpox vaccination programs has led to dwindling acquired immunity in the world population thus raising the risk of epidemic extension of several Orthopoxvirus zoonoses (e.g., monkeypox). Thirdly stocks of camelpox virus which is very similar to Smallpox virus and was intended for biological warfare were discovered during the Gulf War in 1991 and pose a potentially serious threat. Finally official stocks of Smallpox virus could be stolen and used by bioterrorists. Thus reemergence of Orthopoxvirus including smallpox, monkeypox, cowpox, and camelpox is a real danger and contingency planning is needed to define prophylactic and therapeutic strategies to prevent and/or stop an epidemics. Adverse effects from earlier smallpox vaccine (vaccinia) in healthy people or immunocompromised people (congenital or acquired as in HIV infected patients) are absolute contraindications to smallpox vaccination at this time. Further research is needed to develop new vaccines (e.g., attenuated isolates of vaccinia) and effective treatment. This is the only valid reasons for postponing planned destruction of remaining Smallpox virus stocks.

Comparison of the susceptibility of the red fox (Vulpes vulpes) to a vaccinia-rabies recombinant virus and to cowpox virus

Sylvatic rabies can be efficiently controlled by vaccination of foxes with a vaccinia-rabies recombinant virus. However, the risk of recombination between the engineered vaccine virus and other orthopoxviruses endemic in wildlife, such as cowpox virus, still needs to be investigated. In this study, foxes inoculated orally and intradermally with cowpox virus were found to be not very susceptible to cowpox virus, which was isolated from only the oropharynx and tonsils, at low titre and for only five days after inoculation. Thus the risk of recombination between these viruses in foxes is very low.

[The effectiveness of immunization with vaccinia virus type "MVA" against an infection with cowpox virus type "OPV 85" in rabbits]

The immunological efficacy of vacciniavirus "MVA" was tested against a dermal and intradermal infection with cowpoxvirus "OPV 85" in rabbits: A single vaccination with "MVA" provided only insufficient immunity, a revaccination induced good immunity. Intramuscular immunizations protected better than subcutaneous applications. Immunized rabbits showed "revaccination reactions" after infection with "OPV 85" indicating a cellular immunity. After immunization with "MVA" and after infection with cowpoxvirus "OPV 85" all rabbits developed N- and ELISA-antibodies. HAI-antibodies were not found after immunization, but indicated a multiplication of cowpoxvirus after challenge. Vacciniavirus "MVA" is suggested for immunization of man and animal against possible infections with cowpoxvirus and cowpoxlike viruses.