Mosquito transmits

but only the

Sand flies transmit

but only the

Tsetse flies transmit

both

The insect forms are

The mammalian forms are

These multiply inside macrophages. There are a number of forms of leishmania including

which is the most common, and

which is the most severe.

are the major reservoir host. It is a chronic disease with a long incubation period of

to

before clinical symptoms develop

Out of 7.2 billion people

people are at risk. Mainly those in the most

and

countries.

people actually get malaria each year. However deaths have been reduced by about half from

to

thanks to campaigns such as 'roll over malaria'.

of those deaths are in tropical africa.

There are five species in humans

Of these,

causes the greatest morbidity and mortality

The human and chimp lineage diverged around

Previous evidence suggest that P. falciparum originated in chimpanzees as until recently, the closest known relatives of P. falciparum was

the chimp parasite.

As only one p. reichenowi strain was recognised, the two hypotheses as to which diverged could not be tested. However

more strains have now been recognised. Phylogenetic relationships show that P. falciparum and P. reichenowi are the most closely related however

also harbour P. falciparum

It is specifically a disease transmitted between VERTEBRATE animals as diseases transmitted from non-vertebrates are not zoonosis

Lice are highly specialised

ectoparasites. They live on a

host species. They are transmitted by

as they cannot fly or hop like other blood-sucking insects

humans harbour

three

types of louse, each specialised to a seperate ecological niche. These types are

pediculus humanus capitis

pediculus humanus corporis

pthirus pubis. Both the head louse and the body louse are subspecies of

and are thus closely related.

Pediculus humanus corporis are vectors of several important bacterial diseases

Diseases may exert a selection pressure on a population under the following conditions:

or produce fewer offspring

or fail to nurture offspring adequately

In either case the offspring are at a disadvantage

So either

or

Resistant individuals therefore have a

targets the white blood cells. Specifically the

which it uses to enter the white blood cell. Destruction of the CD4 cells leads to a progressive loss of cell-mediated immunity

In

natural resistance to the virus was discovered. Analysis of the cell surface receptors showed a mutation in

This was a 32 BP deletion which causes the protein to become truncated and useless.

CCR5 acts in concert with CD4 in allowing entry of HIV-1 into the cell

This mutation is quite common in europe with

of individuals heterozygous for the mutation and

homozygous.

But this mutation was not selected for by HIV-1 as HIV-1 has only entered our population from great apes in the last

and the origin of the CCR5 mutation dates to 5,000 years