parasitology presentation

Role of the Domestic Chicken (Gallus gallus) in the Epidemitology of Urban

Visceral Leishmaniasis in BrazilBruce Alexander, Renata Lopes de Carvalho, Hamish McCallum and

Marcos Horacio Pereira

E. K. SkoumbourdisDiagnostic Parasitology (MI 520)

August 2012

The Root of Evil??

The ‘Lab’ aka The Favela

Exhibit A: Gallus gallus

Exhibit B: Lutzomyia longipalpis

Photos by R. Wilson

Visceral Leishmaniasis

• Leishmania infantum• Kala-azar, Black Fever• 90% in India, Bangladesh, Nepal,

Sudan, Ethiopia and Brazil.• Febrile illness with weight loss,

enlargement of the spleen and liver.• Decrease in the production of blood

cells that can lead to anemia, bleeding and infections.

Chickens Cannot be Hosts - Physiology

• Body temp of 41° C• Turkey blood meals significantly

reduced Leishmania tropica in Phlebotomus papatasi.

Chickens Cannot Be Hosts – The Math

• The Basic reproductive rate of a vector-transmitted pathogen (R0)

• m = The number of vectors per host• a = The daily biting rate of the vector on

host• b = The vectors that actually generate

infection• p = Daily survival rate of vectors• n = Latent period of infection in vectors• r = Daily recovery rate of hosts𝑹𝟎=

𝒎𝒂𝟐𝒃𝒑𝒙

−𝒓 𝟏𝒏𝒑

Canis

Rattus

Cerdocyon thous

So, Why Blame the Chicken?• Dwellings of individuals with chicken

houses in the yard were 4.21 times more likely to have an individual with Visceral Leishmaniasis.

• 50% egg production• 34.5% for meat• 23.6% for hobby• 9.1% to keep yard trash free• 7.3% for scorpion control• 3.6% for cock fighting

Man vs. Bird ‘Hypothesis’

Man vs. Bird

Why Feed on Chickens?

• Mosquitos produce 2x more eggs per mg of blood when feeding on canaries.

Why Feed on Man?

• Chickens have lower hemoglobin values.

• Chickens have lower hematocrit values.

• Chicken erythrocytes are nucleate and have 31 times more DNA than the human variety.

Comb and Wattle ‘Hypothesis’

Sand Fly Love Nest?

Lekking 101

Not Likely

• Male pheromones have ~2m range.– This is a short range.

• Larvae collection has been unsuccessful.–Nitrogen rich fecal material.

• May go to rodent burrows.– Temperature, humidity and light are

constant.

• No evidence on the predatory chicken behavior towards the sand fly.

Suggestions for Further Research

• Field observations to determine the relative importance of hosts in both blood meals and lekking sites.

• Lab studies of sand fly egg production on chickens vs. other hosts.

• Socioeconomic studies on the importance of the chicken for income and nutrition.

• Education on removal of chicken houses.

The End