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Blood (Intracellular) and Other Tissue Protozoa 95

the salivary glands of the fly after it feeds on an infected trypanosomes in the blood of diseased cattle, but pro-
host. The infective trypanosomes are injected into a new ceeded to show that the organisms caused nagana in
host when the fly again feeds on an uninfected host. The cattle and horses and that the same organisms also were
infection itself causes a number of symptoms including capable of infecting dogs. He determined that all the
anemia, wasting, and lethargy, and in some cases the par- infected cattle had stayed for a period of time in the fly-
asites pass into the brain and cerebrospinal fluid, result- infested “tsetse belt” and that the disease was similar to
ing in coma and death. that in humans. Common names for the disease included
The disease is widespread because similar parasites “negro lethargy” and “fly disease of hunters.”
are found in a large variety of both wild and domesticated
animals. The first definitive accounts of sleeping sickness Morphology
were by an English naval surgeon, John Atkins, in 1721
and Thomas Winterbottom in 1803 (Cox, 2002) showing The causative organisms for the two species of human
humans as a reservoir for the organism (Figure 4-14). An infections in Africa, T. gambiense and T. rodesiense, are
appreciation of the real cause of the disease was not pos- part of the T. brucei-gambiense-rhodesiense complex.
sible until Pasteur had established the germ theory toward T. brucei is believed to be responsible for a wild type of
the end of the nineteenth century as microorganisms were the organism found chiefly in wild game that over time
not yet discovered. Besides herd animals, trypanosomes has evolved to a form that gave rise to the two variants.
have been discovered in the blood of fishes, frogs, and The “tsetse fly belt” widely confines and limits the ex-
smaller mammals. Knowledge of the disease was well es- tent of infections by the two strains of the organism. The
tablished by 1843, and in 1881 Griffith Evans found try- Glossina genus, the tsetse fly, serves as both the interme-
panosomes in the blood of both horses and camels where diate host and vector for the two forms of the disease. For
the tsetse fly abounded. This infection resulted in a wasting the Gambian version of the disease, two species of Glos-
disease called surra in some areas of Africa and Evans sug- sina, those of G. palpais and G. tachinoides, are vectors
gested that the parasites might be the cause of this disease and intermediate hosts. A large portion of the African
(Cox, 2002). Upon the completion of these observations continent is known as the “fly belt” and for this reason
by Evans, the most important discoveries about human and is almost uninhabited by both humans and domesticated
animal trypanosomiasis followed a short time afterwards. animals because of the danger of trypanosomiasis. The
Two years after Evans’s discovery, David Bruce, a wet lowlands and rainforests found in West and Central
British army surgeon, was investigating an outbreak of Africa provide breeding grounds for the tsetse flies, con-
nagana, a disease similar to surra, in cattle in Zululand. tributing to widespread infection. The infection often
He was looking for a bacterial cause but instead found leads to central nervous system derangement and even-
tually death ensues after several years.

Symptoms
Source: Centers for Disease Control and Prevention (CDC) Three stages ensue upon infection through the bite of an

infected tsetse fly. Symptoms differ slightly between the
East African and West African strains. In the East African
variety, the tsetse bite is often painful and therefore read-
ily noticed. The site of the bite develops into a red sore
called a chancre. After 1 to 4 weeks other symptoms arise
including fever, irritability, headache, extreme fatigue,

signs and symptoms are often accompanied by weight
loss and body rash. Infection of the central nervous sys-
tem (CNS) may be manifested by confusion, changes in
FIGURE 4-14 Humans are the main reservoir for muscle and joint pain, and swollen lymph glands. These
Trypanosoma brucei gambiense, but animals are also moods and affect (emotional reaction), slurred speech
susceptible and even seizures, and difficulty walking and talking.