Field of Science

HIV & Measles - double hit pathogenesis?
Despite ongoing worldwide eradication efforts, measles infection still results in significant morbidity and mortality. Although, throughout most of the developed world measles infection has been considerably reduced there still exists massive (and deadly) outbreaks in areas such as Africa and South-East Asia. Investigation of the reasons why this disparity occurs therefore  is of major medical, political and social interest.
Many factors are likely to be behind this major difference - and all of which deserve our attention if we are ever to remove measles from the human population. There exists problems in rolling out vaccines in countries with poor infrastructure such as roads and transport facilities; disruption to what is known as the vaccine 'cold-chain' (vaccines have to be kept cold to avoid rendering them unusable) is likely to occur; general poor health of the population in these regions and possible interference of vaccination in children with high levels of passively acquired maternal antibody.

Measles vaccination efforts in Africa may not be entirely effective
Today in PLoS Pathogens, Nilsson and Chiodi highlight in a featured opinion article, another possible source: the link between co-infection with HIV-1 and Measles infection. They point out that HIV-1 infection and replication may result in impaired immune responses in both mothers and children leaving open the possibility of measles infection (no immune system, no protection). HIV-1, as I'm sure you will all know, is a potentially deadly pandemic retrovirus - particularly a major problem in sub-Saharan Africa- which infects humans where it resides in the bodies own immune system: T cells, dendritic cells and macrophages. Viral replication results in the death of these immune cells and destruction of important lymphoid tissues resulting in an individual without key immune functions.

The authors note that children born to mothers who are HIV-1 positive or are HIV-1 positive themselves develop lower levels of anti-measles antibody upon vaccination -a big deal if we're looking to protect these kids through vaccination. They show that memory B cells may be impaired and lower protection will result through failure to mount a B cell-generated antibody response. Immunity is a highly regulated system, if you remove one aspect-  in this case T cells - you will affect another pathway , in this case B cells. Thus there exists a major  problem with HIV-1 infected people and infection with other pathogens in the environment; HIV-1 infection significantly alters the host immune system weakening it to other invading pathogens such as measles which is endemic in these areas.

So how do we overcome this problem? Well, the authors suggest that on top of increasing vaccination coverage through catch-up programs it would be wise to administer anti-retroviral drugs  to mothers and children prior to vaccination to allow sufficient immune function; this should hopefully make a difference in combating both measles and HIV in the developing world, especially in an area where both cause so much pain. Hopefully, strategies such as this will aid treatment efforts for other pathogens rife in the developing world - targeting both HIV and the individual agents may be more effective.

Sadly, there exists another interaction between HIV and co-infection with other pathogens. Infection usually results in increased levels of immune cells in the blood and tissues yet these very cells are the target for HIV and if these cells increase, HIV replication will also. There exists a deadly interaction between multiple pathogens which must be broken.

Nilsson, A., & Chiodi, F. (2011). Measles Outbreak in Africa—Is There a Link to the HIV-1 Epidemic? PLoS Pathogens, 7 (2) DOI: 10.1371/journal.ppat.1001241

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