Babesia

Piroplasms are protozoan parasites that include Babesia and Theileria. These intracellular tick-borne transmitted diseases are of great economic importance because they are responsible for serious losses in domestic livestock, particularly cattle.

Babesiosis

Babesia bigemina and Babesia bovis are economically important parasites of sheep, cattle, goats, horses, pigs, dogs and cats and are responsible for a disease called babesiosis (redwater fever or tick fever). Babesiosis is transmitted by a number of one-host ticks, such as Boophilus microplus, Boophilus decoloratus, and Boophilus annulatus.

Human babesiosis has been reported mainly in North America and Europe and has been linked to B. bovis, which causes cattle babesiosis. The other parasite linked to human infection is B. microti, a natural parasite of rodents.

Life cycle

The infection begins with a bite by an infected tick, which introduces sporozoites into the blood from it salivary glands. The sporozoites invade the host’s red blood cells and undergo several schizogonic divisions, increasing their numbers enormously. Eventually some of the infected red blood cells rupture, releasing thousands of merozoites and gametocytes into the circulation.

When a tick imbibes blood from an infected animal, the female gamete and male gamete unite in the tick’s gut to produce embryos. Some of these motile embryos or ookinetes migrate through the ticks’ tissues and invade the ovaries where they are incorporated into the developing eggs. Consequently, the ticks lay eggs that are already infected.

The nymphs that arise from such eggs are therefore congenitally infected. Some of the merozoites migrate from the ovaries to the salivary glands of the young ticks and after dividing, give rise to sporozoites. These young ticks are able to pass on the infection directly to a host on taking their first blood meal.

Infected animals show increased body temperature, malaise and loss of appetite, constipation or diarrhoea, vomiting, bloody urine and anaemia. Erythrocytic parasites are present in the lumens of capillaries of all internal organs including the brain. Mortality is high and death may occur in one week.

In human babesiosis, malaise, anorexia and fatigue are usually evident a week after being bitten by an infected tick. These are followed several days later by high fever, chills, drenching sweats, muscle pain and headache. The symptoms may continue for months or abate, then recur. Some infected people do not show any symptoms at all.

Individuals who are at risk are those with reduced immunity, especially the elderly and those who have undergone splenectomy. There is no specific treatment for babesiosis, although antimalarial drugs are sometimes used.