Leishmania parasites are named after W.B. Leishman, who developed one of the earliest stains of Leishmania in 1901. Widespread in 22 countries in the New World and in 66 nations in the Old World, Leishmaniasis is not found in South-east Asia. Human infections are found in 16 countries in Europe, including France, Italy, Greece, Malta, Spain and Portugal. Occurring in several forms, the disease is generally recognized for its cutaneous form which causes non-fatal, disfiguring lesions, although epidemics of the potentially fatal visceral form cause thousands of deaths.

Humans are infected via the bite of Sandflies (subfamily phlebotominae) - tiny sand-coloured blood-feeding flies that breed in forest areas, caves, or the burrows of small rodents. Wild and domesticated animals and humans themselves can act as a reservoir of infection. 

Sheep, goats, cattle, camels and man have been affected in the many subsequent epizootics, which have occurred throughout the Ethiopian faunal region. An extension beyond this range RVF has occurred to Egypt, where a dramatic epizootic in 1997 resulted in much human disease and huge losses amongst the domestic animal populations. RVF cause an acute episode of human disease, with at least 600 deaths and more than 60,000 severe clinical cases. The total morbidity was thought to be measurable in hundreds of thousands, and the resources of the hospitals in the affected areas were severely strained by the numbers of cases presenting daily. Most cases were thought to arise from mosquito bites, but many of the human cases followed close contact with infected animals, and the aerosol route of infection appeared to be responsible.

RVF can be considered to be an emerging zoonotic disease of importance, affecting the domestic livestock populations in Africa, especially where these have been improved by the introduction of genotypes originating in Europe and elsewhere. Indigenous animals appear to have a degree of resistance to the virus. The human disease component has been highly significant in recent East African and West African epizootics.

Bluetongue is an arbovirus, infecting vertebrates and invertebrates cyclically.

Bluetongue virus naturally infects domestic and wild ruminants, camelids and some other herbivores such as elephants. Historically, the primary cycle may have involved species of African antelope, but this role has now been taken over by cattle (Erasmus, 1990).

Midges of the genus Culicoides act as biological vectors of bluetongue virus. Of the approximately 1400 species of Culicoides world-wide, less than 20 are considered actual or possible vectors (OIE, 1998; Mellor, 1990). The most well-studied vector species are C. variipennis and C. insignis in the USA, C. fulvus, C. wadai, C. actoni and C. brevitarsis in Australia, and C. imicola in Africa and the Middle East (Erasmus, 1990). It is possible that additional vector species will be identified in countries such as China and Bulgaria where bluetongue has been recognized only recently.

Sweet itch is a skin condition caused by an allergy to the saliva of small midges called Culicoides. The midges swarm for an hour or two around sunset and are active from around April to October. They tend to bite equines around the tail, head, withers and base of the mane and they like to breed on wet marshy land, dung heaps or dense heavy foliage. The midge’s saliva causes an intense irritation in thousands of horses and ponies.

Affected horses are intensely itchy and rub their manes, tails and sometimes the underside of their bellies until they are red raw and virtually hairless in these areas.

The bites form blisters, which can weep, causing crusting, scabs and scaling. Open sores can often develop. Skin thickening and hair loss pigmentation may occur long-term. There is no cure for the condition - it can only be controlled.

Each year thousands of dogs become disabled or die from lung, heart or circulatory problems caused by heartworm disease. Heartworm disease in dogs and related canines is caused by a filarial nematode (a large thread-like round worm), Dirofilaria immitis. The adult worms live in the right side of the heart (right ventricle) and adjacent blood vessels (pulmonary arteries), and because of their location, are commonly called "dog heartworms."

The complete development of the nematode parasite requires two hosts: dog and mosquito. In the dog, sexually mature adult nematodes are large and cause disease by clogging the heart and major blood vessels leading from the heart. By clogging the main blood a vessel, the blood supply to other organs of the body is reduced, particularly the lungs, liver and kidneys, leading to malfunction of these organs. Once infected a dog is infected for life. The sexually mature nematodes discharge tiny (less than 1/800" long) immature worms called microfilaria into the blood stream of a dog. They do not develop further in the dog, but they can survive in the blood for up to three years. They must be ingested by a mosquito before they can progress further in their development. There is more microfilaria in the blood during the day than at night. Optimum numbers of microfilaria in the blood close to the skin coincide with times of peak feeding activity of mosquitoes. Microfilaria may also be more abundant in the summer when mosquitoes are abundant.