Category Archives: Infectious Diseases Tropical Medicine and Sexually Transmitted Diseases

Sexually transmitted diseases

Sexually transmitted diseases (STDs) remain epidemic in all societies and the range of pathogens that are known to be spread by sex continues to increase. In 1990 over 578000 new cases were seen in genitourinary medicine (GUM) clinics in the UK. In the last 50 years there has been an increase in viral conditions, particularly Herpes simplex virus (HSV) and human papillomavirus, but a decrease in cases of syp

Helminthic (cestode) infections

Tapeworms belong to the subclass Cestoda. These are flat worms measuring a few millimetres (Echinococcus granulosus) to several metres (Taenia saginata) in length. Structurally they consist of a head that is adorned with suckers and hooks (Taenia solium) or suckers alone (T. saginata). The head is attached via a short slender neck to several segments or proglottids that form a chain-like structure or strobil


Fascioliasis Fasciola hepatica infects sheep, goats and cattle, in which it produces liver disease, and is only accidentally transmitted to humans via consumption of wild watercress grown on the grazing land of infected animals. The disease is found worldwide, including the UK. Animals excrete eggs in their faeces, from which ciliated miracidia emerge. These enter the freshwater snail (the intermediate host)

Trematode (fluke) infections

BLOOD INFECTIONS Schistosomiasis (bilharzia) Three major species of schistosomes produce human disease. These have marked differences in geographical distribution. Prevalence is dependent on the presence of a susceptible intermediate snail host and faecal contamination of water supplies. The size of snail populations varies with the season and availability of freshwater breeding grounds. An increase in the worl

Trichuris trichiura (whipworm) infection

T. trichiura is a common parasite and is found worldwide. Prevalence varies from 1% to 90%, being highest in poor communities with inadequate sanitation. Adult worms are most commonly found in the distal ileum and caecum, although in heavy infection no part of the colon is spared. The adult worm embeds its cephalic region into the intestinal mucosa, leaving the distal tail free within the lumen. Such invasio


Some adult nematodes live within the intestinal lumen. The disease is spread to humans: PASSIVELY by ingesting infective eggs, as occurs with Ascaris lumbricoides (’roundworm’), Trichuris trichiura (whipworm) and Enterobius vermicularis (threadworm) ACTIVELY by percutaneous spread of filariform larvae that penetrate the skin (hookworm and Strongyloides) Ascaris deviates from the simplified life-cyc


Onchocerciasis (river blindness) is produced by the filarial bworm Onchocerca volvulus. The gravid female has a life-expectancy of 15 years. The micro filariae are found in the skin and subcutaneous tissue. Humans are the only known definitive host and the day-biting female blackfly of the genus Simulium is the vector. The flies breed in rapidly flowing water both in the rain forest and savannah. The species

Helminthic infections

Nematode (roundworm) infections FILARIASIS Several nematodes belonging to the superfamily Filarioidea are responsible for filariasis. The adult worms are thread-like. Females are larger than males. The viviparous females give birth to larvae known as microfilariae. The microfilariae of various species can be easily differentiated from each other by the presence or absence of a sheath and the pattern of nucle

Intestinal and genital infections

Amoebiasis The most important human disease due to amoebae is amoebiasis, which is caused by Entamoeba histolytica. This intestinal pathogen can be differentiated from other enteric amoebae such as  ntamoeba hartmani, Entamoeba coli and Endolimax nana, since E. histolytica is the only amoeba found in the intestine that phagocytoses RBCs. It occurs worldwide, although much higher incidence rates are found  


The incubation period varies, being: • 10-14 days in P. vivax, P. ovale and P. falciparum • 18 days to 6 weeks in P. malariae infection Although individual variations in clinical presentation are noted, febrile paroxysms, anaemia, splenomegaly and · epatomegaly are usually present. Malarial febrile paroxms typically have three stages: 1 The ‘cold stage’ is characterized by marked vasoconstricti