Vector-Borne Diseases:Trypanosomiasis

April 1st, 2010

The Pathogen

• Genus Trypanosoma• Two species of human health

importance:– Trypanosoma brucei – Trypanosoma cruzi

• The T. brucei complex (2 subspecies):– Trypanosoma brucei rhodesiense – Trypanosoma brucei gambiense – Cannot tell them apart by morphology– Cause distinct disease entities

The Pathogen

• Protozoan hemoflagellates – Single celled– flagella

• Complex life cycle– Vector– Human– animals

• Reservoirs: – Humans– Cattle

The Pathogen

Trypanosoma brucei ssp. in thin blood smears stained with Giemsa.

Overview

• Three types of trypanosomiasis– West African (sleeping sickness)– East African (sleeping sickness)– American (Chaga’s disease)

• Differences– Geographic distribution– Vectors– Disease process

West African Trypanosomiasis

• Sleeping sickness• Trypanosoma brucei gambiense • Geographic distribution

– Western and Central Africa– Vector distribution

• Always fatal without treatment• Disease course over years

– acute and chronic phases

West African Trypanosomiasis

• This form is ~95% of reported cases• 12,000-15,000 reported cases/year,

WHO estimates 50-60,000 are really infected

• Humans are the reservoir• Disease of rural areas; urban

transmission is rare

East African Trypanosomes

• Trypanosoma brucei rhodesiense• Geographic distribution

– East and Southeast Africa

• Always fatal without treatment• Acute course compared to

gambiense form• Cattle are additional reservoir

Cases of African trypanosomiasis

Geographic distribution

Geographic distribution

The vector

• Tsetse fly• Glossina species• Takes a blood meal• trypomastigotes are the form

transmitted to the host• Daytime feeder• Savannah and riverine flies

Life Cycle: Trypanosomes

Disease• Length of disease process differs between

two• Sore may develop at site of initial inoculation

– hemolymphatic stage– fever, lymphadenopathy, and pruritus. 

• meningoencephalitic stage – Parasite crosses blood-brain barrier– invasion of the central nervous system– headaches, somnolence, abnormal behavior– loss of consciousness and coma

• more acute disease with T. b. rhodesiense than T. b. gambiense.

Immunity

• Humans do mount immune response• No residual immunity• cyclic fluctuation in the number of

parasites in blood • Each new wave of parasite

represents a different antigenic variant

Diagnosis

• Microscopic examination– chancre fluid– lymph node aspirates– Blood– bone marrow– cerebrospinal fluid (late stages of

infection) 

• smear stained with Giemsa

Treatment

• Pentamidine isethionate– hemolymphatic stage of West African

• suramin – hemolymphatic stage of East African

• Melarsoprol – arsenical– late disease with central nervous system involvement– T.b. gambiense or T. b. rhodiense

• Eflornithine – Expensive– not widely available – effective only for West African

Control

• Bite prevention– Difficult with daytime biters

• Control vector habitats• Treat infected people

– Screening methods are available

• Bednets not useful

Vector control

• Control with insecticides– sequential aerosol spraying technique

(SAT)– ground spraying– insecticide-treated targets or

insecticide-treated animals

• Traps• sterile insect technique (SIT).

American trypanosomiasis

• Chaga’s Disease• Trypanosoma cruzi • Geographic distribution

– southern United States to southern Argentina

• A disease of poor, rural areas of Mexico, Central America, and South America

• Humans and animals are reservoir

Geographic distribution

Vector

• triatomine bugs (kissing bugs)• Triatoma, Rhodinius, and

Panstrongylus • Takes a blood meal • Releases trypomastigotes in its feces

near the site of the bite • Enter host through the wound

Life Cycle: Chaga’s disease

Disease

• Acute phase– usually asymptomatic– fever, anorexia, lymphadenopathy, myocarditis– Lesion (chagoma) at site of inoculation

• Resolve over a period of a few weeks or months into an asymptomatic chronic form– 20-30% of cases

• Years or decades after initial infection:– cardiomyopathy – GI complications– can be fatal

Diagnosis

• Microscopic examination– fresh anticoagulated blood– thin and thick blood smears stained

with Giemsa• Isolation of the agent:

– inoculation in culture with specialized media

– inoculation into mice– xenodiagnosis

Treatment

• Benznidazole• nifurtimox • Treatment is most effective during

the acute phase• Drugs are fairly toxic• IND protocol from the CDC

Control

• Vector control• Poorly constructed houses and houses

with thatched roofs are at risk• Treatment of houses with insecticides• Get rid of places in dwellings where

vector and reservoir animals can live and breed

• Bednets