As of July 2022, two people have been been diagnosed with monkeypox in New Zealand. Both men appear to have acquired the infection overseas.
Both are very likely to have been advised to isolate at home, and both may be expected to recover completely in the next couple of weeks. It is expected that, by following simple precautions recommended by Public Health specialists, they will not transmit the infection to others in New Zealand. However, it will not be surprising if other cases of infection do occur in New Zealand in the coming months.
So what is this virus and why is it causing such concern now? The monkeypox virus is closely related to other pox viruses that have a long history of causing disease in humans. Smallpox was a major cause of severe disease and death from the time of the pharaohs. It was eradicated by immunisation with a vaccine that contained viable cowpox virus, the cause of a relatively mild disease of cows, horses, rodents and cats. Dairy maids with a history of cowpox were recognised to be immune to smallpox, which led to cowpox vaccination campaigns in many nations from 1800, and the eventual eradication of smallpox in 1977. The origin of smallpox is uncertain, but is presumed to have been a closely related pox virus that infected rodents in Africa thousands of years ago. The main source of cowpox is also rodents, and cats occasionally acquire infection from rodents and may then transmit cowpox to humans.
Monkeypox has great similarities with these two other closely related pox viruses. Its natural hosts, in central and West Africa, include rodents. Outbreaks of human cases intermittently occur in Africa as the result of people coming into contact with the skin of infected wild rodents, or with the skin of other wild or domesticated animals that have themselves been in contact with an infected rodent.
Monkeys are not the usual hosts, but may suffer infection in the same manner as humans. The name is misleading. The virus was first identified in 1958 in monkeys in captivity in Denmark, with the first recognised human case a child in the Democratic Republic of Congo in 1970.
Infection is transmitted by contact either with the skin lesions of an infected animal or human, or with respiratory secretions contaminated by fluid leaking from sores inside the mouth. The virus has been identified in ejaculate, raising concern that it may be transmitted by genital fluids. Following infection there is an asymptomatic incubation period that usually lasts one to two weeks. This is usually followed by the development of headache, fever, muscle aches, tiredness and swollen lymph nodes. Sores develop in the mouth and a few days later the rash appears as scattered red patches on the skin.
Over the course of days each patch progresses to become a papule, which then forms a blister, that initially contains clear fluid which then becomes cloudy. The blister dries and the scab falls off. The scattered patches appear in successive waves that usually appear first on the head, and the skin around the genitals, and then spread centrifugally to the skin of the limbs, and then of the hands and feet. The skin rash usually resolves after two to three weeks. Once the scabs have fallen off the person is no longer infectious. A photograph, that clearly shows multiple typical skin lesions, in varying stages of development, on the face of a young European man with monkeypox, is available here .
The disease is usually suspected in people who report activities that might have brought them into close contact with an infected animal or person, and who have the characteristic rash and other associated features. The diagnosis is confirmed when PCR testing detects the monkeypox DNA in swabs from blisters on the unwell person. Testing of blister fluid for the DNA of monkeypox virus can be performed by laboratories in New Zealand.
The disease can be severe and it has been reported that approximately three percent of cases in Nigeria and approximately 10 percent of cases in the Democratic Republic of the Congo were fatal. However, there have been less than 10 fatalities in several thousand cases in the West in recent months.
A remarkable feature of the monkeypox cases in the current epidemic in mostly high income countries in Europe and the Americas is that virtually all cases are in men, with the overwhelming majority being men who have sex with men (MSM). In contrast, the male predominance has been much less marked in cases that have previously occurred in Africa. The marked concentration of cases in men in the current epidemic suggests that we may be witnessing the emergence of a new sexually transmitted infection (STI), that as with many other STIs, predominantly affects MSM. Further research is necessary to determine whether the concentration of virus is particularly high in ejaculate and other fluids shared during sexual activity.
Almost all patients with active monkeypox will be able to isolate at home. They should use precautions similar to those recommended for patients with COVID-19. However it is especially important that skin to skin contact should be avoided. Contact with contaminated clothing or bedding also should be prevented, by the use of gloves, and careful hand hygieneshould be performed after handling these or other potentially contaminated items.
Cowpox vaccination, which until the 1960s was used to prevent smallpox, is effective in preventing monkeypox. More modern versions of the cowpox vaccine (such as ACAM2000 and JYNNEOS) have been developed and approved for use in humans, but their efficacy has not been extensively investigated. Two antiviral agents, Cidofovir, and Tecovirimat have been approved for use, as has immune globulin purified from the blood of people who have received cowpox vaccination.
The present outbreak of monkeypox has resulted in more than 7,500 confirmed cases (at the time of writing), most of which have occurred in a variety of European countries, the UK, US and Canada. The first case in this outbreak occurred in a British resident who had travelled to Nigeria and then returned to the UK on 4 May. Subsequent cases have largely occurred in MSM, and many early cases appear to have been linked to attendance at a Gay Pride festival in the Canary Islands or a fetish festival in Belgium. Close contact during sex is presumed to have facilitated person to person spread, which has been surprisingly frequent during this outbreak when compared with other outbreaks in the West that have usually affected very small numbers of people.
The daily number of cases by date of onset of symptoms, or diagnosis, or notification, for the epidemics in the UK , Europe and the Americas are shown in Figure 1. While each graph shows a decline in the daily number of cases for the most recent two week period, this may be misleading with regard to the actual new number of cases occurring, because there commonly are delays of about two weeks between onset of illness and notification. It is therefore difficult to predict the course of the epidemic in affected countries during the coming months, and years.