Later the early stage may relapse, or latency may be terminated by the late stage of the disease, which is characterized by soft gummy ulcers of the skin, the bones, and the centre of the face, a patchy loss of skin pigment, and other conditions.
Some studies show that latency and relapse, especially the age-dependent latency and relapse, may affect the transmission dynamics of tuberculosis model.
This is because new infections are much more widely distributed over the year than the peak of clinical cases would imply, as latency of relapse results in clustering of cases.
The molecular mechanisms underlying latency and relapse remain unknown and although the patients' compromised immune system is undoubtedly a contributing factor, changes in the fungal genome may aid the escape from dormancy at the opportune moment.
Latency and relapse may be influenced by external factors, including those related to geography and the seasons, 9 10 11 12 13 but there are few studies large enough to investigate this latency, and it is difficult to explore in endemic areas owing to reinfection.
Tuberculosis, for example, causes acute disease, relapsing disease after prolonged latency and reinfection after definitive treatment.
Following the long latency to first relapse in temperate strains, the interval between subsequent relapses is considerably shorter.
We also found a trend toward a shorter stay in Africa and shorter interval between onset of symptoms and diagnosis among patients with P. ovale wallikeri infection, which could reflect easier transmission, shorter latency, or higher relapse rates.
Additionally, it is possible to answer questions about latency, seasonality, and relapse of vivax in imported cases in non-endemic countries because, unlike endemic countries, reinfection is not a possibility.
With respect to the cost of calculations in estimating the parameters, rather than the straightforward use of the semiparametric Cox cure regression discussed in the previous section, the fitting of parametric cure regression is more reasonable, where the exponential distribution is assumed to be an underlying distribution for the latency time of relapse.
Although analysis methods typically adapt the log-rank statistic for recursive partitioning procedures, the method applied here used a likelihood ratio (LR) test statistic from a fitting of cure survival regression assuming exponential and Weibull distributions for the latency time of relapse.
