Rural areas could be characterised by a lower level of natural immunisation to the infectious agent which may occur either because children have fewer opportunities for person-to-person transmission than in more urban areas, or because the population is not large enough to maintain the disease in an endemic form (Kinlen, 1988).
This grouping most likely signifies that the 1998 outbreak strains re-emerged from older strains that have been maintained in the endemic area since the early 1970s, i.e. from 1975 to 1998 (23 years).
These viruses are endemic in poultry in Eurasia, continue to reassort with other as yet unidentified influenza viruses, and maintain the human receptor specificity (R. Webster).
This constitutes a serious epidemiological scenario, in which the neediest population has been gathered throughout peripheral areas without infrastructure, and thereby destroying natural environments and establishing suitable conditions for maintaining the transmission cycle of this endemic disease in new areas, such as the case in Porto de Galinhas.
However, protected areas still remain vital for maintaining the full complement of species, especially flightless endemics.
To maintain an endemic state, I* must be much greater than 1, otherwise infection will fade-out due to stochastic processes [ 7].
In order for a disease to maintain an endemic infection, there must be a reliable source of susceptible hosts and high enough transmission rates from infected to susceptible individuals (Burdon et al. 1995; Ericson et al. 1999).
It is obvious that the persistence of enteric viruses in water contributes to maintain endemic diseases.
What regions are more likely to maintain endemic cholera?
This may be related to the fact that the poultry density in Cambodia is lower (average 94 heads/km) (9 ) compared with that in neighboring countries such as Thailand and Vietnam (average 640 heads/km) (10 ), and one may speculate that a minimum density of poultry is required for maintaining an endemic virus.
