Smallpox Pneumonia (Smallpox Handler's Lung)

There is no good evidence that any patient with smallpox develops pneumonia, except for a rather vague mention by Chadwick in 1843 of a "pneumonic illness" in vaccinated contacts. Because his patients were immunized, they probably had smallpox handler's lung.

The connection between a pulmonary illness and contact with smallpox was first made and clearly recorded in 1944. Seven hospital staff caring for smallpox patients in the Middle East developed malaise, headaches, and fever up to 41°C (104°F) and suffered from chills and sweating. They had no cough. Physical signs (crepitations particularly) were more widespread than the abnormal changes seen on chest radiographs. By the 3rd day of the illness, six of the seven patients had fine diffuse mottling throughout the lungs, but particularly in the lower lobes. In the mid and lower lung fields there were also rounded opacities. It took up to 6 weeks before all the abnormal chest radiographs became normal, and sulfonamide therapy made no difference to the rate of clearing.

In 1962 there were three similar cases, all contacts with active smallpox by vaccinated and well-immunized staff. In the same year there was a severe outbreak of smallpox in Wales; 54 patients were infected and 17 died. They were looked after by 32 nurses, amongst whom 12 developed chest symptoms 9 to 12 days after contact. They described it as being like "flu without any catarrah!" They had the same severe frontal headache, profuse sweating, malaise, and cough, with fever to 40°C (103.4°F). Three had an erythematous rash. None responded to antibiotics, but in all the fever slowly resolved. All laboratory tests, including skin and nasopharyngeal samples, were negative for the variola virus. All serological tests, including those for allergy, were negative. In six of the nurses, chest radiographs showed 5 to 15 mm opacities of varying density. Some were alveolar, described as "blotchy," while others were interstitial. These opacities slowly cleared in 6 to 8 weeks. The conclusion was that there was no evidence of smallpox pneumonia, but there must have been an allergic reaction in immune hosts to some antigen, perhaps the virus in droplets or skin scale (dust).

In 1974 the six nurses who had abnormal chest radiographs 12 years earlier were all reexamined. Five had developed multiple calcified nodules, mainly in the upper segments of both lungs. The calcification occurred in 4 to 7 years and there was no relationship between the calcified lesions and the previous lung changes seen 12 years earlier, nor was there any relationship to the severity or extent of the physical signs. None had calcifications before, except for one known healed tuberculous focus. One nurse again had a chest radiograph after 30 years and there was no further change (Fig.40.9). There do not seem to have been any related lung function abnormalities at any stage, nor were any laboratory data helpful. The nurses, incidentally, had been working in several different hospitals when in contact with their smallpox patients, and none of those patients with smallpox had lung infections.

Fig. 40.9. Smallpox handler's lung. Bilateral nodular calcification in the lungs of a nurse who had cared for active cases of smallpox 30 years earlier. This will only occur in contacts who are immune to smallpox (Courtesy of Dr. D.R. Foster, FRCR, and the British Journal of Radiology 1994).

The erythematous rash in some contacts is significant. In 1908 it was noted that 10% of smallpox patients developed a prodromal rash; they were all partially immune and their disease was subsequently mild. The tissue reaction to the variola and varicella viruses is similar, although the viruses have a different structure. It is probable that this pulmonary illness resulted from the inhalation of many smallpox viruses, in droplets or dust (e.g., while making patient's beds). In highly immune attendants this caused a modified variola pneumonia, at the same time both similar to and different from chickenpox (varicella) pneumonia. This is well known to cause pulmonary calcifications which become apparent after the clinical infection has resolved.

Thus smallpox handler's lung is yet another rare cause of multiple calcified pulmonary nodules but, unlike the others, this source will slowly fade away because without contact with smallpox (and prior immunization) the pneumonia will never develop. If the last case of smallpox was in 1974, this part of the chapter will soon also be part of the historical record. Anyone who has ever seen a patient suffering from smallpox, particularly a child with severe osteomyelitis, will be quite pleased that it has been conquered.

Monkeypox

Humanity is (or was) the only reservoir of, and sufferer from, smallpox. Monkeypox (tanapox) is genetically distinct from smallpox. There are probably two forms, seen in West Africa and in the former Zaire. The reservoir host is probably squirrels, and, apart from monkeys, the great apes and also anteaters may be infected. The first outbreak of human infection (80 cases) was reported in 1970, in an area from which smallpox had been eliminated. In the following years over 400 cases were reported, the vast majority in the former Zaire, now the Democratic Republic of Congo. For example, there were over 100 cases in an outbreak between July and August 1997 (reported by Reuters Ltd., 31 July 1997). Transmission from animals to humans has previously been confirmed, and it is probable that there is now human to human transmission also. Indeed, this mode of transmission may now account for most cases, though increased consumption of animals carrying monkeypox and discontinuation of vaccination against smallpox were also suggested as possible sources of the 1997 outbreak. Clinically, monkeypox resembles smallpox, with some minor variations; all ages are affected. It can be very difficult to differentiate from varicella. About 10%-15% of those infected will die, the same fatality rate as from smallpox. Vaccination, using the vaccinia virus, provides protection from monkeypox, as it does from smallpox. There have not been any significant reports on specific imaging findings (as of 1999).