Porcine babesiosis

Porcine babesiosis

D T DE WAAL

Introduction

Porcine babesiosis is a tick-transmitted, protozoal disease caused by either Babesia trautmanni or Babesia perroncitoi and characterized by fever, anaemia, icterus and haemoglobinuria. Babesia perroncitoi does not occur in southern Africa.

The disease was first reported in Russia in 1911 by Dementjew.7 According to Knuth and Du Toit the first reliable description of the disease was given by Trautmann who studied the condition in Tanzania in 1914.7 The protozoan concerned was later named Babesia trautmanni.7 In 1939, Cerruti identified another protozoan parasite in the red blood cells of pigs in Italy which were exhibiting clinical signs of babesiosis, and he named this parasite Babesia perroncitoi. 1 Babesia trautmanni also occurs in pigs in Zaire9 and Nigeria.3, 14 More recently, B. perroncitoi has been identified in pigs in Egypt5 and Senegal.19

In southern Africa, porcine babesiosis was described in 1948 in pigs near the Pongola River in the south-eastern region of the Limpopo Province, South Africa,6 and in Zimbabwe. 8 It was also reported in 1958 in the Soutpansberg district in the Limpopo Province.12 In all three outbreaks the causative organism was B. trautmanni.

Although the disease is probably endemic in large parts of southern Africa, it is seldom reported and is not considered economically important.

Aetiology and life cycle

Babesia trautmanni is a large Babesia found in the red blood cells of infected pigs. The merozoites (which are usually paired) measure 2,5–4 × 1,5–2μm and are oval or pyriform in shape. Single forms, probably trophozoites, are amoeboid or round. The host cell usually contains between one and four parasites.

Babesia perroncitoi is smaller than B. trautmanni, the majority of parasites being pleomorphic, annular and measuring 0,7 to 2 μm in diameter.

A variety of other forms, such as oval, quadrangular, and pyriform, also occur. These vary in size from 1,2 to 2,6 μm in length and 0,7 to 1,9 μm in width.1

The life cycles of the organisms in the tick vector are as yet unknown.

Epidemiology

Clinical cases of babesiosis caused by B. trautmanni have only been observed in domestic pigs in southern Africa. The bushpig (Potamochoerus porcus) has been shown to be capable of harbouring the parasite for at least 24 days after artificial infection, but without apparent disease occurring.17

The disease could potentially occur in those parts of southern Africa where the tick vector(s) and bushpigs are found. Bushpigs are particularly associated with forests, thickets, riparian undercover, reed beds or heavy cover of tall grass where there is water.18 Agricultural developments have favoured them. In South Africa, bushpigs occur in the Limpopo Province, eastern parts of Mpumalanga, central and eastern KwaZulu-Natal, and along the coast in the Eastern Cape Province. They also occur in Zimbabwe, Botswana and Mozambique south of the Zambezi River. They are widespread but do not occur in the more arid west of Zimbabwe, while in Botswana they are mainly confined to the Okavango Swamps and adjacent river systems.18 They have not been recorded in Namibia.18

Infection is probably endemic in domestic pigs kept under free-ranging systems of management in endemic areas, but clinical disease is rare. Although intensely farmed pigs are usually not exposed to the parasites, clinical cases of babesiosis may occur when they are turned out to pasture, or when infected ticks are introduced into pigsties via grass used for bedding.

Circumstantial evidence suggests that the ticks Boophilus decoloratus7 and Rhipicephalus turanicus13 are the vectors of B. trautmanni in Africa, but, it was only relatively recently that B. trautmanni was succesfully transmitted with Rhipicephalus simus2 and Rhipicephalus turanicus.10

The nymph and adult progeny of experimentally infected female R. simus and R. turanicus ticks transmitted the infection to pigs. The prepatent period varied from 6 to 15 days after tick infestation. Attempts at transmitting the disease with Hyalomma marginatum, Hyalomma truncatum, Hyalomma marginatum rufipes, Rhipicephalus sanguineus, Rhipicephalus maculatus, Rhipicephalus rossicus, Amblyomma hebraeum and Dermacentor silvarum have failed.10, 13 The possibility of mechanical transmission by haematophagous flies, such as tabanids and Stomoxys spp., has been suggested.3

Although not proven, R. sanguineus, Dermacentor reticulatus and Hyalomma aegyptium have been suggested as vectors of B. perroncitoi in Europe.1

Clinical signs and pathology

Babesiosis caused by B. trautmanni is a mild disease4, 11, 12 which, in endemic situations, usually only results in severe clinical signs when the animals are under stress, such as that caused by malnutrition or helminth infestations. Healthy adult pigs exposed to infection for the first time, however, may contract a severe or even fatal disease.

The disease is less severe in younger pigs than in adults. Clinical signs include listlessness, fever, anorexia and anaemia. Icterus and haemoglobinuria may appear during the later stages of the disease and abortions may result.

Necropsy findings include anaemia, icterus, a slight increasein volume of the fluids in the body cavities, pulmonary congestion and oedema, petechiae on the serous membranes, epi- and endocardial haemorrhages, splenomegaly, and hepatomegaly with pigmentation.

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