Madagascar is an island first explored by the Portuguese in 1500. But it did not have a stable Catholic mission, in Antananarivo until 1861, around the same time that the Protestants establish their missions as well.
An island dedicated to the Immaculate Conception
The first evangelizers were Dominicans friars. These were tragically killed soon after their arrival, first in 1540, and again in 1585. It was only in 1642, with the French occupation of Antongil Bay, that a regular evangelization began, under the auspices of Mary. A small island south of the bay was dedicated to the Virgin Mary in 1642, around then a church on the Malagasy mainland, in 1650.
The arrival of Father Dalmond in 1837 brought a new missionary impetus. Fr. Dalmond became an apostolic prefect and in 1844, he placed his first mission under the patronage of the Immaculate Conception – 10 years before the official proclamation of the dogma!
A popular song commemorates these facts:
"O Mary, mother without stain,
We the Malagasy people,
As our support and our strength "
In 1908, the liturgical directory stated that December 8 was the feast of the Immaculate Conception, patron saint of Madagascar. 
The "tsangam-bato" dedicated to Mary
Images of Mary are found in private houses and out in the countryside, on "tsangam-bato," stone monuments that the Malagasy people usually erect in memory of an important event. The "tsangam-batos" dedicated to Mary recall the event of the Incarnation, and of the Redemption.
Shrines and pilgrimages
There are no national shrines, but cathedrals dedicated to Mary and regional shrines, among which is the shrine of Ambohimanga, popuar with the youth of the capital. There is also the church of Anosivolakely, alleged to have received an apparition and where pilgrimages take place three times a year, accompanied by the clergy.
Tananarive: The Immaculate Conception
Majunga: The Immaculate Heart of Mary
Antsirabe: Our Lady of La Salette
Tsiroanomandidy: Our Lady of the Good Remedy
Morondava: Our Lady of La Salette
Ambohimanga (21 km from Tananarive, a place of pilgrimage, especially for the young people of Antananarivo who go there on foot). 
 Attilio Galli, Madre della Chiesa dei Cinque Continenti, Ed Segno, Udine, 1997, p. 705-712
 A. Boudou, Les jésuites à Madagascar au XIX° siècle, Paris 1942, Vol II, p. 118